compiler/stdc/strncmp.c

   1 /*
   2     Copyright © 1995-2001, The AROS Development Team. All rights reserved.
   3     $Id$
   4
   5     C function strncmp().
   6 */
   7
   8 /*****************************************************************************
   9
  10     NAME */
  11 #include <string.h>
  12
  13         int strncmp (
  14
  15 /*  SYNOPSIS */
  16         const char * str1,
  17         const char * str2,
  18         size_t       n)
  19
  20 /*  FUNCTION
  21         Calculate str1 - str2 for upto n chars or upto the first 0 byte.
  22
  23     INPUTS
  24         str1, str2 - Strings to compare
  25
  26     RESULT
  27         The difference of the strings. The difference is 0, if both are
  28         equal, < 0 if str1 < str2 and > 0 if str1 > str2. Note that
  29         it may be greater then 1 or less than -1.
  30
  31     NOTES
  32         This function is not part of a library and may thus be called
  33         any time.
  34
  35     EXAMPLE
  36
  37     BUGS
  38
  39     SEE ALSO
  40
  41     INTERNALS
  42
  43 ******************************************************************************/
  44 {
  45     /*
  46         If n == 0, then this will not be initialized, even though it is
  47         returned at the end, so we say two strings of 0 length are equal
  48     */
  49     int diff = 0;
  50
  51     /* No need to check *str2 since: a) str1 is equal str2 (both are 0),
  52         then *str1 will terminate the loop b) str1 and str2 are not equal
  53         (eg. *str2 is 0), then the diff part will be FALSE. I calculate
  54         the diff first since a) it's more probable that the first chars
  55         will be different and b) I don't need to initialize diff then. */
  56     while (n && !(diff = *(unsigned char*) str1 - *(unsigned char*) str2) && *str1)
  57     {
  58         /* advance both strings. I do that here, since doing it in the
  59             check above would mean to advance the strings once too often */
  60         str1 ++;
  61         str2 ++;
  62         n --;
  63     }
  64
  65     /* Now return the difference. */
  66     return diff;
  67 } /* strncmp */
  68