/* 
    loop.c - Copyright (C) 1997 Murray Nesbitt (websrc@nesbitt.ca)

    This program is protected and licensed under the following terms and
    conditions: 1) it may not be redistributed in binary form without the
    explicit permission of the author; 2) when redistributed in source
    form, in whole or in part, this complete copyright statement must
    remain intact.
*/

/*
   Usage: loop [-o|x] start end [increment] [width]

   Prints to stdout a series of numbers from `start' to `end', with
   optional increment and zero-padded field width.  Hex (-x) or octal
   (-o) output formats are available.  Negative numbers are allowed,
   and a negative `increment' does the expected thing.

    Examples:

        $ loop 1 3
        1
        2
        3

        $ loop 2 6 2
        2
        4
        6

        $ loop 2 10 2 2
        02
        04
        06
        08
        10

        $ # Create 10 test files, 'test01' through 'test10'
        $ for i in `loop 1 10 1 2`; do touch test$i; done

        $ loop -x -8 8 4 8
        FFFFFFF8
        FFFFFFFC
        00000000
        00000004
        00000008

        $ loop 4 0 -1
        4
        3
        2
        1
        0

 */

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>  /* isalpha() */

/* Format specifier for hex and octal numbers. If you prefer lowercase
   hex numbers, change 'X' to 'x'.
 */
#define HEX_CHAR   'X'
#define OCTAL_CHAR 'o'

/* This needs to be at least long enough to build up a format string of
   the form "%0[INTMAX]d\n".
 */
#define FORMATLENGTH 20

void usage(char *prog)
{
    fprintf(stderr, "Usage: %s [-o|x] start end [increment] [width]\n", prog);
    exit(EXIT_FAILURE);
}

int main(int argc, char **argv)
{
char radix_char = 'd';  /* default to decimal output. */
int i = 1;
long start, end, padding, increment = 1;
char format[FORMATLENGTH], *chr;

    if (argc < 3)
        usage(argv[0]);

    chr = argv[i];
    if (*chr++ == '-' && isalpha((int)*chr)) {
        if ((*chr == 'o' || *chr == 'x') && *(chr + 1) == '\0' && argc > 3) {
            radix_char = (char)(*chr == 'o' ? OCTAL_CHAR : HEX_CHAR);
            i++;
        }
        else usage(argv[0]);
    }

    /* We know these two arguments exist. */
    start = atol(argv[i++]);
    end = atol(argv[i++]);

    if (argc > i && (increment = atol(argv[i++])) == 0) {
        usage(argv[0]);
    }

    /* Yet another argument. */
    if (argc > i) {
        padding = atol(argv[i]);
        sprintf(format, "%%0%ldl%c\n", padding, radix_char);
    }
    else sprintf(format, "%%l%c\n", radix_char);
    
    if (increment > 0) {
        for (i = start; i <= end; i += increment) {
            printf(format, i);
        }
    }
    else {
        for (i = start; i >= end; i += increment) {
            printf(format, i);
        }
    }

    exit(EXIT_SUCCESS);
}