newlib/libc/machine/riscv/strlen.c

   1 /* Copyright (c) 2017  SiFive Inc. All rights reserved.
   2
   3    This copyrighted material is made available to anyone wishing to use,
   4    modify, copy, or redistribute it subject to the terms and conditions
   5    of the FreeBSD License.   This program is distributed in the hope that
   6    it will be useful, but WITHOUT ANY WARRANTY expressed or implied,
   7    including the implied warranties of MERCHANTABILITY or FITNESS FOR
   8    A PARTICULAR PURPOSE.  A copy of this license is available at
   9    http://www.opensource.org/licenses.
  10 */
  11
  12 #include <string.h>
  13 #include <stdint.h>
  14
  15 size_t strlen(const char *str)
  16 {
  17   const char *start = str;
  18
  19 #if defined(PREFER_SIZE_OVER_SPEED) || defined(__OPTIMIZE_SIZE__)
  20   while (*str++)
  21     ;
  22   return str - start - 1;
  23 #else
  24   if (__builtin_expect ((uintptr_t)str & (sizeof (long) - 1), 0)) do
  25     {
  26       char ch = *str;
  27       str++;
  28       if (!ch)
  29         return str - start - 1;
  30     } while ((uintptr_t)str & (sizeof (long) - 1));
  31
  32   unsigned long *ls = (unsigned long *)str;
  33   while (!__libc_detect_null (*ls++))
  34     ;
  35   asm volatile ("" : "+r"(ls)); /* prevent "optimization" */
  36
  37   str = (const char *)ls;
  38   size_t ret = str - start, sl = sizeof (long);
  39
  40   char c0 = str[0 - sl], c1 = str[1 - sl], c2 = str[2 - sl], c3 = str[3 - sl];
  41   if (c0 == 0)            return ret + 0 - sl;
  42   if (c1 == 0)            return ret + 1 - sl;
  43   if (c2 == 0)            return ret + 2 - sl;
  44   if (sl == 4 || c3 == 0) return ret + 3 - sl;
  45
  46   c0 = str[4 - sl], c1 = str[5 - sl], c2 = str[6 - sl], c3 = str[7 - sl];
  47   if (c0 == 0)            return ret + 4 - sl;
  48   if (c1 == 0)            return ret + 5 - sl;
  49   if (c2 == 0)            return ret + 6 - sl;
  50
  51   return ret + 7 - sl;
  52 #endif /* not PREFER_SIZE_OVER_SPEED */
  53 }