libc/string/i386/strnlen.c

   1 /*
   2  * This string-include defines all string functions as inline
   3  * functions. Use gcc. It also assumes ds=es=data space, this should be
   4  * normal. Most of the string-functions are rather heavily hand-optimized,
   5  * see especially strtok,strstr,str[c]spn. They should work, but are not
   6  * very easy to understand. Everything is done entirely within the register
   7  * set, making the functions fast and clean. String instructions have been
   8  * used through-out, making for "slightly" unclear code :-)
   9  *
  10  *              NO Copyright (C) 1991, 1992 Linus Torvalds,
  11  *              consider these trivial functions to be PD.
  12  */
  13
  14 /*
  15  * Copyright (C) 2000-2005 Erik Andersen <andersen@uclibc.org>
  16  *
  17  * Licensed under the LGPL v2.1, see the file COPYING.LIB in this tarball.
  18  */
  19
  20 /*
  21  * Modified for uClibc by Erik Andersen <andersen@codepoet.org>
  22  * These make no attempt to use nifty things like mmx/3dnow/etc.
  23  * These are not inline, and will therefore not be as fast as
  24  * modifying the headers to use inlines (and cannot therefore
  25  * do tricky things when dealing with const memory).  But they
  26  * should (I hope!) be faster than their generic equivalents....
  27  *
  28  * More importantly, these should provide a good example for
  29  * others to follow when adding arch specific optimizations.
  30  *  -Erik
  31  */
  32
  33 #include <string.h>
  34
  35 #ifdef __USE_GNU
  36
  37 #undef strnlen
  38 /*#define strnlen TESTING*/
  39 size_t strnlen(const char *s, size_t count)
  40 {
  41         int edx;
  42         int eax;
  43         __asm__ __volatile__(
  44                 "       leal    -1(%%ecx), %%eax\n"
  45                 "1:     incl    %%eax\n"
  46                 "       decl    %%edx\n"
  47                 "       jz      3f\n"
  48                 "       cmpb    $0, (%%eax)\n"
  49                 "       jnz     1b\n"
  50                 "3:     subl    %%ecx, %%eax"
  51                 : "=a" (eax), "=&d" (edx)
  52                 : "c" (s), "1" (count + 1)
  53         );
  54         return eax;
  55 }
  56 #ifndef strnlen
  57 libc_hidden_def(strnlen)
  58 #else
  59 /* Uncomment TESTING, gcc -D_GNU_SOURCE -m32 -Os strnlen.c -o strnlen
  60  * and run ./strnlen
  61  */
  62 int main()
  63 {
  64         printf(strnlen("abc\0def", -2) == 3 ? "ok\n" : "BAD!\n");
  65         printf(strnlen("abc\0def", -1) == 3 ? "ok\n" : "BAD!\n");
  66         printf(strnlen("abc\0def", 0) == 0 ? "ok\n" : "BAD!\n");
  67         printf(strnlen("abc\0def", 1) == 1 ? "ok\n" : "BAD!\n");
  68         printf(strnlen("abc\0def", 2) == 2 ? "ok\n" : "BAD!\n");
  69         printf(strnlen("abc\0def", 3) == 3 ? "ok\n" : "BAD!\n");
  70         printf(strnlen("abc\0def", 4) == 3 ? "ok\n" : "BAD!\n");
  71         printf(strnlen("abc\0def", 5) == 3 ? "ok\n" : "BAD!\n");
  72 }
  73 #endif
  74
  75 #endif