Dies ist gperf.info, hergestellt von Makeinfo Version 4.3 aus
gperf.texi.

INFO-DIR-SECTION Programming Tools
START-INFO-DIR-ENTRY
* Gperf: (gperf).                Perfect Hash Function Generator.
END-INFO-DIR-ENTRY

   This file documents the features of the GNU Perfect Hash Function
Generator 3.0.1.

   Copyright (C) 1989-2003 Free Software Foundation, Inc.

   Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.

   Permission is granted to copy and distribute modified versions of
this manual under the conditions for verbatim copying, provided also
that the section entitled "GNU General Public License" is included
exactly as in the original, and provided that the entire resulting
derived work is distributed under the terms of a permission notice
identical to this one.

   Permission is granted to copy and distribute translations of this
manual into another language, under the above conditions for modified
versions, except that the section entitled "GNU General Public License"
and this permission notice may be included in translations approved by
the Free Software Foundation instead of in the original English.


File: gperf.info,  Node: Top,  Next: Copying,  Prev: (dir),  Up: (dir)

Introduction
************

   This manual documents the GNU `gperf' perfect hash function generator
utility, focusing on its features and how to use them, and how to report
bugs.

* Menu:

* Copying::                     GNU `gperf' General Public License says
                                how you can copy and share `gperf'.
* Contributors::                People who have contributed to `gperf'.
* Motivation::                  The purpose of `gperf'.
* Search Structures::           Static search structures and GNU `gperf'
* Description::                 High-level discussion of how GPERF functions.
* Options::                     A description of options to the program.
* Bugs::                        Known bugs and limitations with GPERF.
* Projects::                    Things still left to do.
* Bibliography::                Material Referenced in this Report.

* Concept Index::


High-Level Description of GNU `gperf'

* Input Format::                Input Format to `gperf'
* Output Format::               Output Format for Generated C Code with `gperf'
* Binary Strings::              Use of NUL bytes

Input Format to `gperf'

* Declarations::                Declarations.
* Keywords::                    Format for Keyword Entries.
* Functions::                   Including Additional C Functions.
* Controls for GNU indent::     Where to place directives for GNU `indent'.

Declarations

* User-supplied Struct::        Specifying keywords with attributes.
* Gperf Declarations::          Embedding command line options in the input.
* C Code Inclusion::            Including C declarations and definitions.

Invoking `gperf'

* Input Details::               Options that affect Interpretation of the Input File
* Output Language::             Specifying the Language for the Output Code
* Output Details::              Fine tuning Details in the Output Code
* Algorithmic Details::         Changing the Algorithms employed by `gperf'
* Verbosity::                   Informative Output


File: gperf.info,  Node: Copying,  Next: Contributors,  Prev: Top,  Up: Top

GNU GENERAL PUBLIC LICENSE
**************************

                         Version 2, June 1991
     Copyright (C) 1989, 1991 Free Software Foundation, Inc.,
     59 Temple Place, Suite 330, Boston, MA 02111-1307, USA.
     
     Everyone is permitted to copy and distribute verbatim copies
     of this license document, but changing it is not allowed.

Preamble
========

   The licenses for most software are designed to take away your
freedom to share and change it.  By contrast, the GNU General Public
License is intended to guarantee your freedom to share and change free
software--to make sure the software is free for all its users.  This
General Public License applies to most of the Free Software
Foundation's software and to any other program whose authors commit to
using it.  (Some other Free Software Foundation software is covered by
the GNU Library General Public License instead.)  You can apply it to
your programs, too.

   When we speak of free software, we are referring to freedom, not
price.  Our General Public Licenses are designed to make sure that you
have the freedom to distribute copies of free software (and charge for
this service if you wish), that you receive source code or can get it
if you want it, that you can change the software or use pieces of it in
new free programs; and that you know you can do these things.

   To protect your rights, we need to make restrictions that forbid
anyone to deny you these rights or to ask you to surrender the rights.
These restrictions translate to certain responsibilities for you if you
distribute copies of the software, or if you modify it.

   For example, if you distribute copies of such a program, whether
gratis or for a fee, you must give the recipients all the rights that
you have.  You must make sure that they, too, receive or can get the
source code.  And you must show them these terms so they know their
rights.

   We protect your rights with two steps: (1) copyright the software,
and (2) offer you this license which gives you legal permission to copy,
distribute and/or modify the software.

   Also, for each author's protection and ours, we want to make certain
that everyone understands that there is no warranty for this free
software.  If the software is modified by someone else and passed on, we
want its recipients to know that what they have is not the original, so
that any problems introduced by others will not reflect on the original
authors' reputations.

   Finally, any free program is threatened constantly by software
patents.  We wish to avoid the danger that redistributors of a free
program will individually obtain patent licenses, in effect making the
program proprietary.  To prevent this, we have made it clear that any
patent must be licensed for everyone's free use or not licensed at all.

   The precise terms and conditions for copying, distribution and
modification follow.

    TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
  0. This License applies to any program or other work which contains a
     notice placed by the copyright holder saying it may be distributed
     under the terms of this General Public License.  The "Program",
     below, refers to any such program or work, and a "work based on
     the Program" means either the Program or any derivative work under
     copyright law: that is to say, a work containing the Program or a
     portion of it, either verbatim or with modifications and/or
     translated into another language.  (Hereinafter, translation is
     included without limitation in the term "modification".)  Each
     licensee is addressed as "you".

     Activities other than copying, distribution and modification are
     not covered by this License; they are outside its scope.  The act
     of running the Program is not restricted, and the output from the
     Program is covered only if its contents constitute a work based on
     the Program (independent of having been made by running the
     Program).  Whether that is true depends on what the Program does.

  1. You may copy and distribute verbatim copies of the Program's
     source code as you receive it, in any medium, provided that you
     conspicuously and appropriately publish on each copy an appropriate
     copyright notice and disclaimer of warranty; keep intact all the
     notices that refer to this License and to the absence of any
     warranty; and give any other recipients of the Program a copy of
     this License along with the Program.

     You may charge a fee for the physical act of transferring a copy,
     and you may at your option offer warranty protection in exchange
     for a fee.

  2. You may modify your copy or copies of the Program or any portion
     of it, thus forming a work based on the Program, and copy and
     distribute such modifications or work under the terms of Section 1
     above, provided that you also meet all of these conditions:

       a. You must cause the modified files to carry prominent notices
          stating that you changed the files and the date of any change.

       b. You must cause any work that you distribute or publish, that
          in whole or in part contains or is derived from the Program
          or any part thereof, to be licensed as a whole at no charge
          to all third parties under the terms of this License.

       c. If the modified program normally reads commands interactively
          when run, you must cause it, when started running for such
          interactive use in the most ordinary way, to print or display
          an announcement including an appropriate copyright notice and
          a notice that there is no warranty (or else, saying that you
          provide a warranty) and that users may redistribute the
          program under these conditions, and telling the user how to
          view a copy of this License.  (Exception: if the Program
          itself is interactive but does not normally print such an
          announcement, your work based on the Program is not required
          to print an announcement.)

     These requirements apply to the modified work as a whole.  If
     identifiable sections of that work are not derived from the
     Program, and can be reasonably considered independent and separate
     works in themselves, then this License, and its terms, do not
     apply to those sections when you distribute them as separate
     works.  But when you distribute the same sections as part of a
     whole which is a work based on the Program, the distribution of
     the whole must be on the terms of this License, whose permissions
     for other licensees extend to the entire whole, and thus to each
     and every part regardless of who wrote it.

     Thus, it is not the intent of this section to claim rights or
     contest your rights to work written entirely by you; rather, the
     intent is to exercise the right to control the distribution of
     derivative or collective works based on the Program.

     In addition, mere aggregation of another work not based on the
     Program with the Program (or with a work based on the Program) on
     a volume of a storage or distribution medium does not bring the
     other work under the scope of this License.

  3. You may copy and distribute the Program (or a work based on it,
     under Section 2) in object code or executable form under the terms
     of Sections 1 and 2 above provided that you also do one of the
     following:

       a. Accompany it with the complete corresponding machine-readable
          source code, which must be distributed under the terms of
          Sections 1 and 2 above on a medium customarily used for
          software interchange; or,

       b. Accompany it with a written offer, valid for at least three
          years, to give any third party, for a charge no more than your
          cost of physically performing source distribution, a complete
          machine-readable copy of the corresponding source code, to be
          distributed under the terms of Sections 1 and 2 above on a
          medium customarily used for software interchange; or,

       c. Accompany it with the information you received as to the offer
          to distribute corresponding source code.  (This alternative is
          allowed only for noncommercial distribution and only if you
          received the program in object code or executable form with
          such an offer, in accord with Subsection b above.)

     The source code for a work means the preferred form of the work for
     making modifications to it.  For an executable work, complete
     source code means all the source code for all modules it contains,
     plus any associated interface definition files, plus the scripts
     used to control compilation and installation of the executable.
     However, as a special exception, the source code distributed need
     not include anything that is normally distributed (in either
     source or binary form) with the major components (compiler,
     kernel, and so on) of the operating system on which the executable
     runs, unless that component itself accompanies the executable.

     If distribution of executable or object code is made by offering
     access to copy from a designated place, then offering equivalent
     access to copy the source code from the same place counts as
     distribution of the source code, even though third parties are not
     compelled to copy the source along with the object code.

  4. You may not copy, modify, sublicense, or distribute the Program
     except as expressly provided under this License.  Any attempt
     otherwise to copy, modify, sublicense or distribute the Program is
     void, and will automatically terminate your rights under this
     License.  However, parties who have received copies, or rights,
     from you under this License will not have their licenses
     terminated so long as such parties remain in full compliance.

  5. You are not required to accept this License, since you have not
     signed it.  However, nothing else grants you permission to modify
     or distribute the Program or its derivative works.  These actions
     are prohibited by law if you do not accept this License.
     Therefore, by modifying or distributing the Program (or any work
     based on the Program), you indicate your acceptance of this
     License to do so, and all its terms and conditions for copying,
     distributing or modifying the Program or works based on it.

  6. Each time you redistribute the Program (or any work based on the
     Program), the recipient automatically receives a license from the
     original licensor to copy, distribute or modify the Program
     subject to these terms and conditions.  You may not impose any
     further restrictions on the recipients' exercise of the rights
     granted herein.  You are not responsible for enforcing compliance
     by third parties to this License.

  7. If, as a consequence of a court judgment or allegation of patent
     infringement or for any other reason (not limited to patent
     issues), conditions are imposed on you (whether by court order,
     agreement or otherwise) that contradict the conditions of this
     License, they do not excuse you from the conditions of this
     License.  If you cannot distribute so as to satisfy simultaneously
     your obligations under this License and any other pertinent
     obligations, then as a consequence you may not distribute the
     Program at all.  For example, if a patent license would not permit
     royalty-free redistribution of the Program by all those who
     receive copies directly or indirectly through you, then the only
     way you could satisfy both it and this License would be to refrain
     entirely from distribution of the Program.

     If any portion of this section is held invalid or unenforceable
     under any particular circumstance, the balance of the section is
     intended to apply and the section as a whole is intended to apply
     in other circumstances.

     It is not the purpose of this section to induce you to infringe any
     patents or other property right claims or to contest validity of
     any such claims; this section has the sole purpose of protecting
     the integrity of the free software distribution system, which is
     implemented by public license practices.  Many people have made
     generous contributions to the wide range of software distributed
     through that system in reliance on consistent application of that
     system; it is up to the author/donor to decide if he or she is
     willing to distribute software through any other system and a
     licensee cannot impose that choice.

     This section is intended to make thoroughly clear what is believed
     to be a consequence of the rest of this License.

  8. If the distribution and/or use of the Program is restricted in
     certain countries either by patents or by copyrighted interfaces,
     the original copyright holder who places the Program under this
     License may add an explicit geographical distribution limitation
     excluding those countries, so that distribution is permitted only
     in or among countries not thus excluded.  In such case, this
     License incorporates the limitation as if written in the body of
     this License.

  9. The Free Software Foundation may publish revised and/or new
     versions of the General Public License from time to time.  Such
     new versions will be similar in spirit to the present version, but
     may differ in detail to address new problems or concerns.

     Each version is given a distinguishing version number.  If the
     Program specifies a version number of this License which applies
     to it and "any later version", you have the option of following
     the terms and conditions either of that version or of any later
     version published by the Free Software Foundation.  If the Program
     does not specify a version number of this License, you may choose
     any version ever published by the Free Software Foundation.

 10. If you wish to incorporate parts of the Program into other free
     programs whose distribution conditions are different, write to the
     author to ask for permission.  For software which is copyrighted
     by the Free Software Foundation, write to the Free Software
     Foundation; we sometimes make exceptions for this.  Our decision
     will be guided by the two goals of preserving the free status of
     all derivatives of our free software and of promoting the sharing
     and reuse of software generally.

                                NO WARRANTY

 11. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO
     WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE
     LAW.  EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT
     HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT
     WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT
     NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
     FITNESS FOR A PARTICULAR PURPOSE.  THE ENTIRE RISK AS TO THE
     QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU.  SHOULD THE
     PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY
     SERVICING, REPAIR OR CORRECTION.

 12. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN
     WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY
     MODIFY AND/OR REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE
     LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL,
     INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR
     INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
     DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU
     OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY
     OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN
     ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.

                      END OF TERMS AND CONDITIONS

How to Apply These Terms to Your New Programs
=============================================

   If you develop a new program, and you want it to be of the greatest
possible use to the public, the best way to achieve this is to make it
free software which everyone can redistribute and change under these
terms.

   To do so, attach the following notices to the program.  It is safest
to attach them to the start of each source file to most effectively
convey the exclusion of warranty; and each file should have at least
the "copyright" line and a pointer to where the full notice is found.

     ONE LINE TO GIVE THE PROGRAM'S NAME AND AN IDEA OF WHAT IT DOES.
     Copyright (C) YEAR  NAME OF AUTHOR
     
     This program is free software; you can redistribute it and/or
     modify it under the terms of the GNU General Public License
     as published by the Free Software Foundation; either version 2
     of the License, or (at your option) any later version.
     
     This program is distributed in the hope that it will be useful,
     but WITHOUT ANY WARRANTY; without even the implied warranty of
     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
     GNU General Public License for more details.
     
     You should have received a copy of the GNU General Public License
     along with this program; if not, write to the Free Software
     Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA.

   Also add information on how to contact you by electronic and paper
mail.

   If the program is interactive, make it output a short notice like
this when it starts in an interactive mode:

     Gnomovision version 69, Copyright (C) YEAR  NAME OF AUTHOR
     Gnomovision comes with ABSOLUTELY NO WARRANTY; for details
     type `show w'.  This is free software, and you are welcome
     to redistribute it under certain conditions; type `show c'
     for details.

   The hypothetical commands `show w' and `show c' should show the
appropriate parts of the General Public License.  Of course, the
commands you use may be called something other than `show w' and `show
c'; they could even be mouse-clicks or menu items--whatever suits your
program.

   You should also get your employer (if you work as a programmer) or
your school, if any, to sign a "copyright disclaimer" for the program,
if necessary.  Here is a sample; alter the names:

     Yoyodyne, Inc., hereby disclaims all copyright
     interest in the program `Gnomovision'
     (which makes passes at compilers) written
     by James Hacker.
     
     SIGNATURE OF TY COON, 1 April 1989
     Ty Coon, President of Vice

   This General Public License does not permit incorporating your
program into proprietary programs.  If your program is a subroutine
library, you may consider it more useful to permit linking proprietary
applications with the library.  If this is what you want to do, use the
GNU Library General Public License instead of this License.


File: gperf.info,  Node: Contributors,  Next: Motivation,  Prev: Copying,  Up: Top

Contributors to GNU `gperf' Utility
***********************************

   * The GNU `gperf' perfect hash function generator utility was
     written in GNU C++ by Douglas C. Schmidt.  The general idea for
     the perfect hash function generator was inspired by Keith Bostic's
     algorithm written in C, and distributed to net.sources around
     1984.  The current program is a heavily modified, enhanced, and
     extended implementation of Keith's basic idea, created at the
     University of California, Irvine.  Bugs, patches, and suggestions
     should be reported to `<bug-gnu-gperf@gnu.org>'.

   * Special thanks is extended to Michael Tiemann and Doug Lea, for
     providing a useful compiler, and for giving me a forum to exhibit
     my creation.

     In addition, Adam de Boor and Nels Olson provided many tips and
     insights that greatly helped improve the quality and functionality
     of `gperf'.

   * Bruno Haible enhanced and optimized the search algorithm.  He also
     rewrote the input routines and the output routines for better
     reliability, and added a testsuite.


File: gperf.info,  Node: Motivation,  Next: Search Structures,  Prev: Contributors,  Up: Top

Introduction
************

   `gperf' is a perfect hash function generator written in C++.  It
transforms an N element user-specified keyword set W into a perfect
hash function F.  F uniquely maps keywords in W onto the range 0..K,
where K >= N-1.  If K = N-1 then F is a _minimal_ perfect hash function.
`gperf' generates a 0..K element static lookup table and a pair of C
functions.  These functions determine whether a given character string
S occurs in W, using at most one probe into the lookup table.

   `gperf' currently generates the reserved keyword recognizer for
lexical analyzers in several production and research compilers and
language processing tools, including GNU C, GNU C++, GNU Java, GNU
Pascal, GNU Modula 3, and GNU indent.  Complete C++ source code for
`gperf' is available from `http://ftp.gnu.org/pub/gnu/gperf/'.  A paper
describing `gperf''s design and implementation in greater detail is
available in the Second USENIX C++ Conference proceedings or from
`http://www.cs.wustl.edu/~schmidt/resume.html'.


File: gperf.info,  Node: Search Structures,  Next: Description,  Prev: Motivation,  Up: Top

Static search structures and GNU `gperf'
****************************************

   A "static search structure" is an Abstract Data Type with certain
fundamental operations, e.g., _initialize_, _insert_, and _retrieve_.
Conceptually, all insertions occur before any retrievals.  In practice,
`gperf' generates a _static_ array containing search set keywords and
any associated attributes specified by the user.  Thus, there is
essentially no execution-time cost for the insertions.  It is a useful
data structure for representing _static search sets_.  Static search
sets occur frequently in software system applications.  Typical static
search sets include compiler reserved words, assembler instruction
opcodes, and built-in shell interpreter commands.  Search set members,
called "keywords", are inserted into the structure only once, usually
during program initialization, and are not generally modified at
run-time.

   Numerous static search structure implementations exist, e.g.,
arrays, linked lists, binary search trees, digital search tries, and
hash tables.  Different approaches offer trade-offs between space
utilization and search time efficiency.  For example, an N element
sorted array is space efficient, though the average-case time
complexity for retrieval operations using binary search is proportional
to log N.  Conversely, hash table implementations often locate a table
entry in constant time, but typically impose additional memory overhead
and exhibit poor worst case performance.

   _Minimal perfect hash functions_ provide an optimal solution for a
particular class of static search sets.  A minimal perfect hash
function is defined by two properties:

   * It allows keyword recognition in a static search set using at most
     _one_ probe into the hash table.  This represents the "perfect"
     property.

   * The actual memory allocated to store the keywords is precisely
     large enough for the keyword set, and _no larger_.  This is the
     "minimal" property.

   For most applications it is far easier to generate _perfect_ hash
functions than _minimal perfect_ hash functions.  Moreover, non-minimal
perfect hash functions frequently execute faster than minimal ones in
practice.  This phenomena occurs since searching a sparse keyword table
increases the probability of locating a "null" entry, thereby reducing
string comparisons.  `gperf''s default behavior generates
_near-minimal_ perfect hash functions for keyword sets.  However,
`gperf' provides many options that permit user control over the degree
of minimality and perfection.

   Static search sets often exhibit relative stability over time.  For
example, Ada's 63 reserved words have remained constant for nearly a
decade.  It is therefore frequently worthwhile to expend concerted
effort building an optimal search structure _once_, if it subsequently
receives heavy use multiple times.  `gperf' removes the drudgery
associated with constructing time- and space-efficient search
structures by hand.  It has proven a useful and practical tool for
serious programming projects.  Output from `gperf' is currently used in
several production and research compilers, including GNU C, GNU C++,
GNU Java, GNU Pascal, and GNU Modula 3.  The latter two compilers are
not yet part of the official GNU distribution.  Each compiler utilizes
`gperf' to automatically generate static search structures that
efficiently identify their respective reserved keywords.


File: gperf.info,  Node: Description,  Next: Options,  Prev: Search Structures,  Up: Top

High-Level Description of GNU `gperf'
*************************************

* Menu:

* Input Format::                Input Format to `gperf'
* Output Format::               Output Format for Generated C Code with `gperf'
* Binary Strings::              Use of NUL bytes

   The perfect hash function generator `gperf' reads a set of
"keywords" from an input file (or from the standard input by default).
It attempts to derive a perfect hashing function that recognizes a
member of the "static keyword set" with at most a single probe into the
lookup table.  If `gperf' succeeds in generating such a function it
produces a pair of C source code routines that perform hashing and
table lookup recognition.  All generated C code is directed to the
standard output.  Command-line options described below allow you to
modify the input and output format to `gperf'.

   By default, `gperf' attempts to produce time-efficient code, with
less emphasis on efficient space utilization.  However, several options
exist that permit trading-off execution time for storage space and vice
versa.  In particular, expanding the generated table size produces a
sparse search structure, generally yielding faster searches.
Conversely, you can direct `gperf' to utilize a C `switch' statement
scheme that minimizes data space storage size.  Furthermore, using a C
`switch' may actually speed up the keyword retrieval time somewhat.
Actual results depend on your C compiler, of course.

   In general, `gperf' assigns values to the bytes it is using for
hashing until some set of values gives each keyword a unique value.  A
helpful heuristic is that the larger the hash value range, the easier
it is for `gperf' to find and generate a perfect hash function.
Experimentation is the key to getting the most from `gperf'.


File: gperf.info,  Node: Input Format,  Next: Output Format,  Prev: Description,  Up: Description

Input Format to `gperf'
=======================

   You can control the input file format by varying certain command-line
arguments, in particular the `-t' option.  The input's appearance is
similar to GNU utilities `flex' and `bison' (or UNIX utilities `lex'
and `yacc').  Here's an outline of the general format:

     declarations
     %%
     keywords
     %%
     functions

   _Unlike_ `flex' or `bison', the declarations section and the
functions section are optional.  The following sections describe the
input format for each section.

* Menu:

* Declarations::                Declarations.
* Keywords::                    Format for Keyword Entries.
* Functions::                   Including Additional C Functions.
* Controls for GNU indent::     Where to place directives for GNU `indent'.

   It is possible to omit the declaration section entirely, if the `-t'
option is not given.  In this case the input file begins directly with
the first keyword line, e.g.:

     january
     february
     march
     april
     ...


File: gperf.info,  Node: Declarations,  Next: Keywords,  Prev: Input Format,  Up: Input Format

Declarations
------------

   The keyword input file optionally contains a section for including
arbitrary C declarations and definitions, `gperf' declarations that act
like command-line options, as well as for providing a user-supplied
`struct'.

* Menu:

* User-supplied Struct::        Specifying keywords with attributes.
* Gperf Declarations::          Embedding command line options in the input.
* C Code Inclusion::            Including C declarations and definitions.


File: gperf.info,  Node: User-supplied Struct,  Next: Gperf Declarations,  Prev: Declarations,  Up: Declarations

User-supplied `struct'
......................

   If the `-t' option (or, equivalently, the `%struct-type' declaration)
_is_ enabled, you _must_ provide a C `struct' as the last component in
the declaration section from the input file.  The first field in this
struct must be of type `char *' or `const char *' if the `-P' option is
not given, or of type `int' if the option `-P' (or, equivalently, the
`%pic' declaration) is enabled.  This first field must be called
`name', although it is possible to modify its name with the `-K' option
(or, equivalently, the `%define slot-name' declaration) described below.

   Here is a simple example, using months of the year and their
attributes as input:

     struct month { char *name; int number; int days; int leap_days; };
     %%
     january,   1, 31, 31
     february,  2, 28, 29
     march,     3, 31, 31
     april,     4, 30, 30
     may,       5, 31, 31
     june,      6, 30, 30
     july,      7, 31, 31
     august,    8, 31, 31
     september, 9, 30, 30
     october,  10, 31, 31
     november, 11, 30, 30
     december, 12, 31, 31

   Separating the `struct' declaration from the list of keywords and
other fields are a pair of consecutive percent signs, `%%', appearing
left justified in the first column, as in the UNIX utility `lex'.

   If the `struct' has already been declared in an include file, it can
be mentioned in an abbreviated form, like this:

     struct month;
     %%
     january,   1, 31, 31
     ...


File: gperf.info,  Node: Gperf Declarations,  Next: C Code Inclusion,  Prev: User-supplied Struct,  Up: Declarations

Gperf Declarations
..................

   The declaration section can contain `gperf' declarations.  They
influence the way `gperf' works, like command line options do.  In
fact, every such declaration is equivalent to a command line option.
There are three forms of declarations:

  1. Declarations without argument, like `%compare-lengths'.

  2. Declarations with an argument, like `%switch=COUNT'.

  3. Declarations of names of entities in the output file, like
     `%define lookup-function-name NAME'.

   When a declaration is given both in the input file and as a command
line option, the command-line option's value prevails.

   The following `gperf' declarations are available.

`%delimiters=DELIMITER-LIST'
     Allows you to provide a string containing delimiters used to
     separate keywords from their attributes.  The default is ",".  This
     option is essential if you want to use keywords that have embedded
     commas or newlines.

`%struct-type'
     Allows you to include a `struct' type declaration for generated
     code; see above for an example.

`%ignore-case'
     Consider upper and lower case ASCII characters as equivalent.  The
     string comparison will use a case insignificant character
     comparison.  Note that locale dependent case mappings are ignored.

`%language=LANGUAGE-NAME'
     Instructs `gperf' to generate code in the language specified by the
     option's argument.  Languages handled are currently:

    `KR-C'
          Old-style K&R C.  This language is understood by old-style C
          compilers and ANSI C compilers, but ANSI C compilers may flag
          warnings (or even errors) because of lacking `const'.

    `C'
          Common C.  This language is understood by ANSI C compilers,
          and also by old-style C compilers, provided that you `#define
          const' to empty for compilers which don't know about this
          keyword.

    `ANSI-C'
          ANSI C.  This language is understood by ANSI C compilers and
          C++ compilers.

    `C++'
          C++.  This language is understood by C++ compilers.

     The default is C.

`%define slot-name NAME'
     This declaration is only useful when option `-t' (or,
     equivalently, the `%struct-type' declaration) has been given.  By
     default, the program assumes the structure component identifier for
     the keyword is `name'.  This option allows an arbitrary choice of
     identifier for this component, although it still must occur as the
     first field in your supplied `struct'.

`%define initializer-suffix INITIALIZERS'
     This declaration is only useful when option `-t' (or,
     equivalently, the `%struct-type' declaration) has been given.  It
     permits to specify initializers for the structure members following
     SLOT-NAME in empty hash table entries.  The list of initializers
     should start with a comma.  By default, the emitted code will
     zero-initialize structure members following SLOT-NAME.

`%define hash-function-name NAME'
     Allows you to specify the name for the generated hash function.
     Default name is `hash'.  This option permits the use of two hash
     tables in the same file.

`%define lookup-function-name NAME'
     Allows you to specify the name for the generated lookup function.
     Default name is `in_word_set'.  This option permits multiple
     generated hash functions to be used in the same application.

`%define class-name NAME'
     This option is only useful when option `-L C++' (or, equivalently,
     the `%language=C++' declaration) has been given.  It allows you to
     specify the name of generated C++ class.  Default name is
     `Perfect_Hash'.

`%7bit'
     This option specifies that all strings that will be passed as
     arguments to the generated hash function and the generated lookup
     function will solely consist of 7-bit ASCII characters (bytes in
     the range 0..127).  (Note that the ANSI C functions `isalnum' and
     `isgraph' do _not_ guarantee that a byte is in this range.  Only
     an explicit test like `c >= 'A' && c <= 'Z'' guarantees this.)

`%compare-lengths'
     Compare keyword lengths before trying a string comparison.  This
     option is mandatory for binary comparisons (*note Binary
     Strings::).  It also might cut down on the number of string
     comparisons made during the lookup, since keywords with different
     lengths are never compared via `strcmp'.  However, using
     `%compare-lengths' might greatly increase the size of the
     generated C code if the lookup table range is large (which implies
     that the switch option `-S' or `%switch' is not enabled), since
     the length table contains as many elements as there are entries in
     the lookup table.

`%compare-strncmp'
     Generates C code that uses the `strncmp' function to perform
     string comparisons.  The default action is to use `strcmp'.

`%readonly-tables'
     Makes the contents of all generated lookup tables constant, i.e.,
     "readonly".  Many compilers can generate more efficient code for
     this by putting the tables in readonly memory.

`%enum'
     Define constant values using an enum local to the lookup function
     rather than with #defines.  This also means that different lookup
     functions can reside in the same file.  Thanks to James Clark
     `<jjc@ai.mit.edu>'.

`%includes'
     Include the necessary system include file, `<string.h>', at the
     beginning of the code.  By default, this is not done; the user must
     include this header file himself to allow compilation of the code.

`%global-table'
     Generate the static table of keywords as a static global variable,
     rather than hiding it inside of the lookup function (which is the
     default behavior).

`%pic'
     Optimize the generated table for inclusion in shared libraries.
     This reduces the startup time of programs using a shared library
     containing the generated code.  If the `%struct-type' declaration
     (or, equivalently, the option `-t') is also given, the first field
     of the user-defined struct must be of type `int', not `char *',
     because it will contain offsets into the string pool instead of
     actual strings.  To convert such an offset to a string, you can
     use the expression `stringpool + O', where O is the offset.  The
     string pool name can be changed through the `%define
     string-pool-name' declaration.

`%define string-pool-name NAME'
     Allows you to specify the name of the generated string pool
     created by the declaration `%pic' (or, equivalently, the option
     `-P').  The default name is `stringpool'.  This declaration
     permits the use of two hash tables in the same file, with `%pic'
     and even when the `%global-table' declaration (or, equivalently,
     the option `-G') is given.

`%null-strings'
     Use NULL strings instead of empty strings for empty keyword table
     entries.  This reduces the startup time of programs using a shared
     library containing the generated code (but not as much as the
     declaration `%pic'), at the expense of one more test-and-branch
     instruction at run time.

`%define word-array-name NAME'
     Allows you to specify the name for the generated array containing
     the hash table.  Default name is `wordlist'.  This option permits
     the use of two hash tables in the same file, even when the option
     `-G' (or, equivalently, the `%global-table' declaration) is given.

`%switch=COUNT'
     Causes the generated C code to use a `switch' statement scheme,
     rather than an array lookup table.  This can lead to a reduction
     in both time and space requirements for some input files.  The
     argument to this option determines how many `switch' statements
     are generated.  A value of 1 generates 1 `switch' containing all
     the elements, a value of 2 generates 2 tables with 1/2 the
     elements in each `switch', etc.  This is useful since many C
     compilers cannot correctly generate code for large `switch'
     statements.  This option was inspired in part by Keith Bostic's
     original C program.

`%omit-struct-type'
     Prevents the transfer of the type declaration to the output file.
     Use this option if the type is already defined elsewhere.


File: gperf.info,  Node: C Code Inclusion,  Prev: Gperf Declarations,  Up: Declarations

C Code Inclusion
................

   Using a syntax similar to GNU utilities `flex' and `bison', it is
possible to directly include C source text and comments verbatim into
the generated output file.  This is accomplished by enclosing the region
inside left-justified surrounding `%{', `%}' pairs.  Here is an input
fragment based on the previous example that illustrates this feature:

     %{
     #include <assert.h>
     /* This section of code is inserted directly into the output. */
     int return_month_days (struct month *months, int is_leap_year);
     %}
     struct month { char *name; int number; int days; int leap_days; };
     %%
     january,   1, 31, 31
     february,  2, 28, 29
     march,     3, 31, 31
     ...


File: gperf.info,  Node: Keywords,  Next: Functions,  Prev: Declarations,  Up: Input Format

Format for Keyword Entries
--------------------------

   The second input file format section contains lines of keywords and
any associated attributes you might supply.  A line beginning with `#'
in the first column is considered a comment.  Everything following the
`#' is ignored, up to and including the following newline.  A line
beginning with `%' in the first column is an option declaration and
must not occur within the keywords section.

   The first field of each non-comment line is always the keyword
itself.  It can be given in two ways: as a simple name, i.e., without
surrounding string quotation marks, or as a string enclosed in
double-quotes, in C syntax, possibly with backslash escapes like `\"'
or `\234' or `\xa8'.  In either case, it must start right at the
beginning of the line, without leading whitespace.  In this context, a
"field" is considered to extend up to, but not include, the first
blank, comma, or newline.  Here is a simple example taken from a
partial list of C reserved words:

     # These are a few C reserved words, see the c.gperf file
     # for a complete list of ANSI C reserved words.
     unsigned
     sizeof
     switch
     signed
     if
     default
     for
     while
     return

   Note that unlike `flex' or `bison' the first `%%' marker may be
elided if the declaration section is empty.

   Additional fields may optionally follow the leading keyword.  Fields
should be separated by commas, and terminate at the end of line.  What
these fields mean is entirely up to you; they are used to initialize the
elements of the user-defined `struct' provided by you in the
declaration section.  If the `-t' option (or, equivalently, the
`%struct-type' declaration) is _not_ enabled these fields are simply
ignored.  All previous examples except the last one contain keyword
attributes.


File: gperf.info,  Node: Functions,  Next: Controls for GNU indent,  Prev: Keywords,  Up: Input Format

Including Additional C Functions
--------------------------------

   The optional third section also corresponds closely with conventions
found in `flex' and `bison'.  All text in this section, starting at the
final `%%' and extending to the end of the input file, is included
verbatim into the generated output file.  Naturally, it is your
responsibility to ensure that the code contained in this section is
valid C.


File: gperf.info,  Node: Controls for GNU indent,  Prev: Functions,  Up: Input Format

Where to place directives for GNU `indent'.
-------------------------------------------

   If you want to invoke GNU `indent' on a `gperf' input file, you will
see that GNU `indent' doesn't understand the `%%', `%{' and `%}'
directives that control `gperf''s interpretation of the input file.
Therefore you have to insert some directives for GNU `indent'.  More
precisely, assuming the most general input file structure

     declarations part 1
     %{
     verbatim code
     %}
     declarations part 2
     %%
     keywords
     %%
     functions

you would insert `*INDENT-OFF*' and `*INDENT-ON*' comments as follows:

     /* *INDENT-OFF* */
     declarations part 1
     %{
     /* *INDENT-ON* */
     verbatim code
     /* *INDENT-OFF* */
     %}
     declarations part 2
     %%
     keywords
     %%
     /* *INDENT-ON* */
     functions


File: gperf.info,  Node: Output Format,  Next: Binary Strings,  Prev: Input Format,  Up: Description

Output Format for Generated C Code with `gperf'
===============================================

   Several options control how the generated C code appears on the
standard output.  Two C function are generated.  They are called `hash'
and `in_word_set', although you may modify their names with a
command-line option.  Both functions require two arguments, a string,
`char *' STR, and a length parameter, `int' LEN.  Their default
function prototypes are as follows:

 - Funktion: unsigned int hash (const char * STR, unsigned int LEN)
     By default, the generated `hash' function returns an integer value
     created by adding LEN to several user-specified STR byte positions
     indexed into an "associated values" table stored in a local static
     array.  The associated values table is constructed internally by
     `gperf' and later output as a static local C array called
     `hash_table'.  The relevant selected positions (i.e. indices into
     STR) are specified via the `-k' option when running `gperf', as
     detailed in the _Options_ section below (*note Options::).

 - Funktion:  in_word_set (const char * STR, unsigned int LEN)
     If STR is in the keyword set, returns a pointer to that keyword.
     More exactly, if the option `-t' (or, equivalently, the
     `%struct-type' declaration) was given, it returns a pointer to the
     matching keyword's structure.  Otherwise it returns `NULL'.

   If the option `-c' (or, equivalently, the `%compare-strncmp'
declaration) is not used, STR must be a NUL terminated string of
exactly length LEN.  If `-c' (or, equivalently, the `%compare-strncmp'
declaration) is used, STR must simply be an array of LEN bytes and does
not need to be NUL terminated.

   The code generated for these two functions is affected by the
following options:

`-t'
`--struct-type'
     Make use of the user-defined `struct'.

`-S TOTAL-SWITCH-STATEMENTS'
`--switch=TOTAL-SWITCH-STATEMENTS'
     Generate 1 or more C `switch' statement rather than use a large,
     (and potentially sparse) static array.  Although the exact time and
     space savings of this approach vary according to your C compiler's
     degree of optimization, this method often results in smaller and
     faster code.

   If the `-t' and `-S' options (or, equivalently, the `%struct-type'
and `%switch' declarations) are omitted, the default action is to
generate a `char *' array containing the keywords, together with
additional empty strings used for padding the array.  By experimenting
with the various input and output options, and timing the resulting C
code, you can determine the best option choices for different keyword
set characteristics.


File: gperf.info,  Node: Binary Strings,  Prev: Output Format,  Up: Description

Use of NUL bytes
================

   By default, the code generated by `gperf' operates on zero
terminated strings, the usual representation of strings in C.  This
means that the keywords in the input file must not contain NUL bytes,
and the STR argument passed to `hash' or `in_word_set' must be NUL
terminated and have exactly length LEN.

   If option `-c' (or, equivalently, the `%compare-strncmp'
declaration) is used, then the STR argument does not need to be NUL
terminated.  The code generated by `gperf' will only access the first
LEN, not LEN+1, bytes starting at STR.  However, the keywords in the
input file still must not contain NUL bytes.

   If option `-l' (or, equivalently, the `%compare-lengths'
declaration) is used, then the hash table performs binary comparison.
The keywords in the input file may contain NUL bytes, written in string
syntax as `\000' or `\x00', and the code generated by `gperf' will
treat NUL like any other byte.  Also, in this case the `-c' option (or,
equivalently, the `%compare-strncmp' declaration) is ignored.


File: gperf.info,  Node: Options,  Next: Bugs,  Prev: Description,  Up: Top

Invoking `gperf'
****************

   There are _many_ options to `gperf'.  They were added to make the
program more convenient for use with real applications.  "On-line" help
is readily available via the `--help' option.  Here is the complete
list of options.

* Menu:

* Output File::                 Specifying the Location of the Output File
* Input Details::               Options that affect Interpretation of the Input File
* Output Language::             Specifying the Language for the Output Code
* Output Details::              Fine tuning Details in the Output Code
* Algorithmic Details::         Changing the Algorithms employed by `gperf'
* Verbosity::                   Informative Output


File: gperf.info,  Node: Output File,  Next: Input Details,  Prev: Options,  Up: Options

Specifying the Location of the Output File
==========================================

`--output-file=FILE'
     Allows you to specify the name of the file to which the output is
     written to.

   The results are written to standard output if no output file is
specified or if it is `-'.


File: gperf.info,  Node: Input Details,  Next: Output Language,  Prev: Output File,  Up: Options

Options that affect Interpretation of the Input File
====================================================

   These options are also available as declarations in the input file
(*note Gperf Declarations::).

`-e KEYWORD-DELIMITER-LIST'
`--delimiters=KEYWORD-DELIMITER-LIST'
     Allows you to provide a string containing delimiters used to
     separate keywords from their attributes.  The default is ",".  This
     option is essential if you want to use keywords that have embedded
     commas or newlines.  One useful trick is to use -e'TAB', where TAB
     is the literal tab character.

`-t'
`--struct-type'
     Allows you to include a `struct' type declaration for generated
     code.  Any text before a pair of consecutive `%%' is considered
     part of the type declaration.  Keywords and additional fields may
     follow this, one group of fields per line.  A set of examples for
     generating perfect hash tables and functions for Ada, C, C++,
     Pascal, Modula 2, Modula 3 and JavaScript reserved words are
     distributed with this release.

`--ignore-case'
     Consider upper and lower case ASCII characters as equivalent.  The
     string comparison will use a case insignificant character
     comparison.  Note that locale dependent case mappings are ignored.
     This option is therefore not suitable if a properly
     internationalized or locale aware case mapping should be used.
     (For example, in a Turkish locale, the upper case equivalent of
     the lowercase ASCII letter `i' is the non-ASCII character `capital
     i with dot above'.)  For this case, it is better to apply an
     uppercase or lowercase conversion on the string before passing it
     to the `gperf' generated function.


File: gperf.info,  Node: Output Language,  Next: Output Details,  Prev: Input Details,  Up: Options

Options to specify the Language for the Output Code
===================================================

   These options are also available as declarations in the input file
(*note Gperf Declarations::).

`-L GENERATED-LANGUAGE-NAME'
`--language=GENERATED-LANGUAGE-NAME'
     Instructs `gperf' to generate code in the language specified by the
     option's argument.  Languages handled are currently:

    `KR-C'
          Old-style K&R C.  This language is understood by old-style C
          compilers and ANSI C compilers, but ANSI C compilers may flag
          warnings (or even errors) because of lacking `const'.

    `C'
          Common C.  This language is understood by ANSI C compilers,
          and also by old-style C compilers, provided that you `#define
          const' to empty for compilers which don't know about this
          keyword.

    `ANSI-C'
          ANSI C.  This language is understood by ANSI C compilers and
          C++ compilers.

    `C++'
          C++.  This language is understood by C++ compilers.

     The default is C.

`-a'
     This option is supported for compatibility with previous releases
     of `gperf'.  It does not do anything.

`-g'
     This option is supported for compatibility with previous releases
     of `gperf'.  It does not do anything.


File: gperf.info,  Node: Output Details,  Next: Algorithmic Details,  Prev: Output Language,  Up: Options

Options for fine tuning Details in the Output Code
==================================================

   Most of these options are also available as declarations in the
input file (*note Gperf Declarations::).

`-K SLOT-NAME'
`--slot-name=SLOT-NAME'
     This option is only useful when option `-t' (or, equivalently, the
     `%struct-type' declaration) has been given.  By default, the
     program assumes the structure component identifier for the keyword
     is `name'.  This option allows an arbitrary choice of identifier
     for this component, although it still must occur as the first
     field in your supplied `struct'.

`-F INITIALIZERS'
`--initializer-suffix=INITIALIZERS'
     This option is only useful when option `-t' (or, equivalently, the
     `%struct-type' declaration) has been given.  It permits to specify
     initializers for the structure members following SLOT-NAME in
     empty hash table entries.  The list of initializers should start
     with a comma.  By default, the emitted code will zero-initialize
     structure members following SLOT-NAME.

`-H HASH-FUNCTION-NAME'
`--hash-function-name=HASH-FUNCTION-NAME'
     Allows you to specify the name for the generated hash function.
     Default name is `hash'.  This option permits the use of two hash
     tables in the same file.

`-N LOOKUP-FUNCTION-NAME'
`--lookup-function-name=LOOKUP-FUNCTION-NAME'
     Allows you to specify the name for the generated lookup function.
     Default name is `in_word_set'.  This option permits multiple
     generated hash functions to be used in the same application.

`-Z CLASS-NAME'
`--class-name=CLASS-NAME'
     This option is only useful when option `-L C++' (or, equivalently,
     the `%language=C++' declaration) has been given.  It allows you to
     specify the name of generated C++ class.  Default name is
     `Perfect_Hash'.

`-7'
`--seven-bit'
     This option specifies that all strings that will be passed as
     arguments to the generated hash function and the generated lookup
     function will solely consist of 7-bit ASCII characters (bytes in
     the range 0..127).  (Note that the ANSI C functions `isalnum' and
     `isgraph' do _not_ guarantee that a byte is in this range.  Only
     an explicit test like `c >= 'A' && c <= 'Z'' guarantees this.)
     This was the default in versions of `gperf' earlier than 2.7; now
     the default is to support 8-bit and multibyte characters.

`-l'
`--compare-lengths'
     Compare keyword lengths before trying a string comparison.  This
     option is mandatory for binary comparisons (*note Binary
     Strings::).  It also might cut down on the number of string
     comparisons made during the lookup, since keywords with different
     lengths are never compared via `strcmp'.  However, using `-l'
     might greatly increase the size of the generated C code if the
     lookup table range is large (which implies that the switch option
     `-S' or `%switch' is not enabled), since the length table contains
     as many elements as there are entries in the lookup table.

`-c'
`--compare-strncmp'
     Generates C code that uses the `strncmp' function to perform
     string comparisons.  The default action is to use `strcmp'.

`-C'
`--readonly-tables'
     Makes the contents of all generated lookup tables constant, i.e.,
     "readonly".  Many compilers can generate more efficient code for
     this by putting the tables in readonly memory.

`-E'
`--enum'
     Define constant values using an enum local to the lookup function
     rather than with #defines.  This also means that different lookup
     functions can reside in the same file.  Thanks to James Clark
     `<jjc@ai.mit.edu>'.

`-I'
`--includes'
     Include the necessary system include file, `<string.h>', at the
     beginning of the code.  By default, this is not done; the user must
     include this header file himself to allow compilation of the code.

`-G'
`--global-table'
     Generate the static table of keywords as a static global variable,
     rather than hiding it inside of the lookup function (which is the
     default behavior).

`-P'
`--pic'
     Optimize the generated table for inclusion in shared libraries.
     This reduces the startup time of programs using a shared library
     containing the generated code.  If the option `-t' (or,
     equivalently, the `%struct-type' declaration) is also given, the
     first field of the user-defined struct must be of type `int', not
     `char *', because it will contain offsets into the string pool
     instead of actual strings.  To convert such an offset to a string,
     you can use the expression `stringpool + O', where O is the
     offset.  The string pool name can be changed through the option
     `--string-pool-name'.

`-Q STRING-POOL-NAME'
`--string-pool-name=STRING-POOL-NAME'
     Allows you to specify the name of the generated string pool
     created by option `-P'.  The default name is `stringpool'.  This
     option permits the use of two hash tables in the same file, with
     `-P' and even when the option `-G' (or, equivalently, the
     `%global-table' declaration) is given.

`--null-strings'
     Use NULL strings instead of empty strings for empty keyword table
     entries.  This reduces the startup time of programs using a shared
     library containing the generated code (but not as much as option
     `-P'), at the expense of one more test-and-branch instruction at
     run time.

`-W HASH-TABLE-ARRAY-NAME'
`--word-array-name=HASH-TABLE-ARRAY-NAME'
     Allows you to specify the name for the generated array containing
     the hash table.  Default name is `wordlist'.  This option permits
     the use of two hash tables in the same file, even when the option
     `-G' (or, equivalently, the `%global-table' declaration) is given.

`-S TOTAL-SWITCH-STATEMENTS'
`--switch=TOTAL-SWITCH-STATEMENTS'
     Causes the generated C code to use a `switch' statement scheme,
     rather than an array lookup table.  This can lead to a reduction
     in both time and space requirements for some input files.  The
     argument to this option determines how many `switch' statements
     are generated.  A value of 1 generates 1 `switch' containing all
     the elements, a value of 2 generates 2 tables with 1/2 the
     elements in each `switch', etc.  This is useful since many C
     compilers cannot correctly generate code for large `switch'
     statements.  This option was inspired in part by Keith Bostic's
     original C program.

`-T'
`--omit-struct-type'
     Prevents the transfer of the type declaration to the output file.
     Use this option if the type is already defined elsewhere.

`-p'
     This option is supported for compatibility with previous releases
     of `gperf'.  It does not do anything.


File: gperf.info,  Node: Algorithmic Details,  Next: Verbosity,  Prev: Output Details,  Up: Options

Options for changing the Algorithms employed by `gperf'
=======================================================

`-k SELECTED-BYTE-POSITIONS'
`--key-positions=SELECTED-BYTE-POSITIONS'
     Allows selection of the byte positions used in the keywords' hash
     function.  The allowable choices range between 1-255, inclusive.
     The positions are separated by commas, e.g., `-k 9,4,13,14';
     ranges may be used, e.g., `-k 2-7'; and positions may occur in any
     order.  Furthermore, the wildcard '*' causes the generated hash
     function to consider *all* byte positions in each keyword, whereas
     '$' instructs the hash function to use the "final byte" of a
     keyword (this is the only way to use a byte position greater than
     255, incidentally).

     For instance, the option `-k 1,2,4,6-10,'$'' generates a hash
     function that considers positions 1,2,4,6,7,8,9,10, plus the last
     byte in each keyword (which may be at a different position for each
     keyword, obviously).  Keywords with length less than the indicated
     byte positions work properly, since selected byte positions
     exceeding the keyword length are simply not referenced in the hash
     function.

     This option is not normally needed since version 2.8 of `gperf';
     the default byte positions are computed depending on the keyword
     set, through a search that minimizes the number of byte positions.

`-D'
`--duplicates'
     Handle keywords whose selected byte sets hash to duplicate values.
     Duplicate hash values can occur if a set of keywords has the same
     names, but possesses different attributes, or if the selected byte
     positions are not well chosen.  With the -D option `gperf' treats
     all these keywords as part of an equivalence class and generates a
     perfect hash function with multiple comparisons for duplicate
     keywords.  It is up to you to completely disambiguate the keywords
     by modifying the generated C code.  However, `gperf' helps you out
     by organizing the output.

     Using this option usually means that the generated hash function
     is no longer perfect.  On the other hand, it permits `gperf' to
     work on keyword sets that it otherwise could not handle.

`-m ITERATIONS'
`--multiple-iterations=ITERATIONS'
     Perform multiple choices of the `-i' and `-j' values, and choose
     the best results.  This increases the running time by a factor of
     ITERATIONS but does a good job minimizing the generated table size.

`-i INITIAL-VALUE'
`--initial-asso=INITIAL-VALUE'
     Provides an initial VALUE for the associate values array.  Default
     is 0.  Increasing the initial value helps inflate the final table
     size, possibly leading to more time efficient keyword lookups.
     Note that this option is not particularly useful when `-S' (or,
     equivalently, `%switch') is used.  Also, `-i' is overridden when
     the `-r' option is used.

`-j JUMP-VALUE'
`--jump=JUMP-VALUE'
     Affects the "jump value", i.e., how far to advance the associated
     byte value upon collisions.  JUMP-VALUE is rounded up to an odd
     number, the default is 5.  If the JUMP-VALUE is 0 `gperf' jumps by
     random amounts.

`-n'
`--no-strlen'
     Instructs the generator not to include the length of a keyword when
     computing its hash value.  This may save a few assembly
     instructions in the generated lookup table.

`-r'
`--random'
     Utilizes randomness to initialize the associated values table.
     This frequently generates solutions faster than using deterministic
     initialization (which starts all associated values at 0).
     Furthermore, using the randomization option generally increases
     the size of the table.

`-s SIZE-MULTIPLE'
`--size-multiple=SIZE-MULTIPLE'
     Affects the size of the generated hash table.  The numeric
     argument for this option indicates "how many times larger or
     smaller" the maximum associated value range should be, in
     relationship to the number of keywords.  It can be written as an
     integer, a floating-point number or a fraction.  For example, a
     value of 3 means "allow the maximum associated value to be about 3
     times larger than the number of input keywords".  Conversely, a
     value of 1/3 means "allow the maximum associated value to be about
     3 times smaller than the number of input keywords".  Values
     smaller than 1 are useful for limiting the overall size of the
     generated hash table, though the option `-m' is better at this
     purpose.

     If `generate switch' option `-S' (or, equivalently, `%switch') is
     _not_ enabled, the maximum associated value influences the static
     array table size, and a larger table should decrease the time
     required for an unsuccessful search, at the expense of extra table
     space.

     The default value is 1, thus the default maximum associated value
     about the same size as the number of keywords (for efficiency, the
     maximum associated value is always rounded up to a power of 2).
     The actual table size may vary somewhat, since this technique is
     essentially a heuristic.


File: gperf.info,  Node: Verbosity,  Prev: Algorithmic Details,  Up: Options

Informative Output
==================

`-h'
`--help'
     Prints a short summary on the meaning of each program option.
     Aborts further program execution.

`-v'
`--version'
     Prints out the current version number.

`-d'
`--debug'
     Enables the debugging option.  This produces verbose diagnostics to
     "standard error" when `gperf' is executing.  It is useful both for
     maintaining the program and for determining whether a given set of
     options is actually speeding up the search for a solution.  Some
     useful information is dumped at the end of the program when the
     `-d' option is enabled.


File: gperf.info,  Node: Bugs,  Next: Projects,  Prev: Options,  Up: Top

Known Bugs and Limitations with `gperf'
***************************************

   The following are some limitations with the current release of
`gperf':

   * The `gperf' utility is tuned to execute quickly, and works quickly
     for small to medium size data sets (around 1000 keywords).  It is
     extremely useful for maintaining perfect hash functions for
     compiler keyword sets.  Several recent enhancements now enable
     `gperf' to work efficiently on much larger keyword sets (over
     15,000 keywords).  When processing large keyword sets it helps
     greatly to have over 8 megs of RAM.

   * The size of the generate static keyword array can get _extremely_
     large if the input keyword file is large or if the keywords are
     quite similar.  This tends to slow down the compilation of the
     generated C code, and _greatly_ inflates the object code size.  If
     this situation occurs, consider using the `-S' option to reduce
     data size, potentially increasing keyword recognition time a
     negligible amount.  Since many C compilers cannot correctly
     generate code for large switch statements it is important to
     qualify the -S option with an appropriate numerical argument that
     controls the number of switch statements generated.

   * The maximum number of selected byte positions has an arbitrary
     limit of 255.  This restriction should be removed, and if anyone
     considers this a problem write me and let me know so I can remove
     the constraint.


File: gperf.info,  Node: Projects,  Next: Bibliography,  Prev: Bugs,  Up: Top

Things Still Left to Do
***********************

   It should be "relatively" easy to replace the current perfect hash
function algorithm with a more exhaustive approach; the perfect hash
module is essential independent from other program modules.  Additional
worthwhile improvements include:

   * Another useful extension involves modifying the program to generate
     "minimal" perfect hash functions (under certain circumstances, the
     current version can be rather extravagant in the generated table
     size).  This is mostly of theoretical interest, since a sparse
     table often produces faster lookups, and use of the `-S' `switch'
     option can minimize the data size, at the expense of slightly
     longer lookups (note that the gcc compiler generally produces good
     code for `switch' statements, reducing the need for more complex
     schemes).

   * In addition to improving the algorithm, it would also be useful to
     generate an Ada package as the code output, in addition to the
     current C and C++ routines.


File: gperf.info,  Node: Bibliography,  Next: Concept Index,  Prev: Projects,  Up: Top

Bibliography
************

   [1] Chang, C.C.: A Scheme for Constructing Ordered Minimal Perfect
Hashing Functions Information Sciences 39(1986), 187-195.

   [2] Cichelli, Richard J. Author's Response to "On Cichelli's Minimal
Perfect Hash Functions Method" Communications of the ACM, 23,
12(December 1980), 729.

   [3] Cichelli, Richard J. Minimal Perfect Hash Functions Made Simple
Communications of the ACM, 23, 1(January 1980), 17-19.

   [4] Cook, C. R. and Oldehoeft, R.R. A Letter Oriented Minimal
Perfect Hashing Function SIGPLAN Notices, 17, 9(September 1982), 18-27.

   [5] Cormack, G. V. and Horspool, R. N. S. and Kaiserwerth, M.
Practical Perfect Hashing Computer Journal, 28, 1(January 1985), 54-58.

   [6] Jaeschke, G. Reciprocal Hashing: A Method for Generating Minimal
Perfect Hashing Functions Communications of the ACM, 24, 12(December
1981), 829-833.

   [7] Jaeschke, G. and Osterburg, G. On Cichelli's Minimal Perfect
Hash Functions Method Communications of the ACM, 23, 12(December 1980),
728-729.

   [8] Sager, Thomas J. A Polynomial Time Generator for Minimal Perfect
Hash Functions Communications of the ACM, 28, 5(December 1985), 523-532

   [9] Schmidt, Douglas C. GPERF: A Perfect Hash Function Generator
Second USENIX C++ Conference Proceedings, April 1990.

   [10] Schmidt, Douglas C. GPERF: A Perfect Hash Function Generator
C++ Report, SIGS 10 10 (November/December 1998).

   [11] Sebesta, R.W. and Taylor, M.A. Minimal Perfect Hash Functions
for Reserved Word Lists  SIGPLAN Notices, 20, 12(September 1985), 47-53.

   [12] Sprugnoli, R. Perfect Hashing Functions: A Single Probe
Retrieving Method for Static Sets Communications of the ACM, 20
11(November 1977), 841-850.

   [13] Stallman, Richard M. Using and Porting GNU CC Free Software
Foundation, 1988.

   [14] Stroustrup, Bjarne The C++ Programming Language.
Addison-Wesley, 1986.

   [15] Tiemann, Michael D. User's Guide to GNU C++ Free Software
Foundation, 1989.


File: gperf.info,  Node: Concept Index,  Prev: Bibliography,  Up: Top

Concept Index
*************

* Menu:

* %%:                                    User-supplied Struct.
* %7bit:                                 Gperf Declarations.
* %compare-lengths:                      Gperf Declarations.
* %compare-strncmp:                      Gperf Declarations.
* %define class-name:                    Gperf Declarations.
* %define hash-function-name:            Gperf Declarations.
* %define initializer-suffix:            Gperf Declarations.
* %define lookup-function-name:          Gperf Declarations.
* %define slot-name:                     Gperf Declarations.
* %define string-pool-name:              Gperf Declarations.
* %define word-array-name:               Gperf Declarations.
* %delimiters:                           Gperf Declarations.
* %enum:                                 Gperf Declarations.
* %global-table:                         Gperf Declarations.
* %ignore-case:                          Gperf Declarations.
* %includes:                             Gperf Declarations.
* %language:                             Gperf Declarations.
* %null-strings:                         Gperf Declarations.
* %omit-struct-type:                     Gperf Declarations.
* %pic:                                  Gperf Declarations.
* %readonly-tables:                      Gperf Declarations.
* %struct-type:                          Gperf Declarations.
* %switch:                               Gperf Declarations.
* %{:                                    C Code Inclusion.
* %}:                                    C Code Inclusion.
* Array name:                            Output Details.
* Bugs:                                  Contributors.
* Class name:                            Output Details.
* Declaration section:                   Input Format.
* Delimiters:                            Input Details.
* Duplicates:                            Algorithmic Details.
* Format:                                Input Format.
* Functions section:                     Input Format.
* hash:                                  Output Format.
* hash table:                            Output Format.
* in_word_set:                           Output Format.
* Initializers:                          Output Details.
* Jump value:                            Algorithmic Details.
* Keywords section:                      Input Format.
* Minimal perfect hash functions:        Search Structures.
* NUL:                                   Binary Strings.
* Slot name:                             Output Details.
* Static search structure:               Search Structures.
* switch <1>:                            Output Details.
* switch:                                Output Format.



Tag Table:
Node: Top1240
Node: Copying3324
Node: Contributors22513
Node: Motivation23706
Node: Search Structures24834
Node: Description28389
Node: Input Format30282
Node: Declarations31419
Node: User-supplied Struct31995
Node: Gperf Declarations33594
Node: C Code Inclusion42004
Node: Keywords42831
Node: Functions44767
Node: Controls for GNU indent45293
Node: Output Format46232
Node: Binary Strings49016
Node: Options50159
Node: Output File50944
Node: Input Details51328
Node: Output Language53159
Node: Output Details54570
Node: Algorithmic Details61485
Node: Verbosity66734
Node: Bugs67437
Node: Projects69029
Node: Bibliography70157
Node: Concept Index72213

End Tag Table
