sysdeps/alpha/strchr.c

   1 /* Copyright (C) 1992, 1993, 1994, 1995 Free Software Foundation, Inc.
   2
   3 The GNU C Library is free software; you can redistribute it and/or
   4 modify it under the terms of the GNU Library General Public License as
   5 published by the Free Software Foundation; either version 2 of the
   6 License, or (at your option) any later version.
   7
   8 The GNU C Library is distributed in the hope that it will be useful,
   9 but WITHOUT ANY WARRANTY; without even the implied warranty of
  10 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  11 Library General Public License for more details.
  12
  13 You should have received a copy of the GNU Library General Public
  14 License along with the GNU C Library; see the file COPYING.LIB.  If
  15 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  16 Cambridge, MA 02139, USA.  */
  17
  18 #include <string.h>
  19
  20 /* Return the length of the null-terminated string STR.  Scan for
  21    the null terminator quickly by testing eight bytes at a time.  */
  22
  23 char *
  24 strchr (const char *str, int c)
  25 {
  26   const char *char_ptr;
  27   const unsigned long int *longword_ptr;
  28   unsigned long int charmask;
  29
  30   c = (unsigned char) c;
  31
  32   /* Handle the first few characters by reading one character at a time.
  33      Do this until STR is aligned on a 8-byte border.  */
  34   for (char_ptr = str; ((unsigned long int) char_ptr & 7) != 0; ++char_ptr)
  35     if (*char_ptr == c)
  36       return (char *) char_ptr;
  37     else if (*char_ptr == '\0')
  38       return NULL;
  39
  40   longword_ptr = (unsigned long int *) char_ptr;
  41
  42   /* Set up a longword, each of whose bytes is C.  */
  43   charmask = c | (c << 8);
  44   charmask |= charmask << 16;
  45   charmask |= charmask << 32;
  46
  47   for (;;)
  48     {
  49       const unsigned long int longword = *longword_ptr++;
  50       int ge, le, zero;
  51
  52       /* Set bits in ZERO if bytes in LONGWORD are zero.  */
  53       asm ("cmpbge $31, %1, %0" : "=r" (zero) : "r" (longword));
  54
  55       /* Set bits in GE if bytes in CHARMASK are >= bytes in LONGWORD.  */
  56       asm ("cmpbge %1, %2, %0" : "=r" (ge) : "r" (charmask), "r" (longword));
  57
  58       /* Set bits in LE if bytes in CHARMASK are <= bytes in LONGWORD.  */
  59       asm ("cmpbge %2, %1, %0" : "=r" (le) : "r" (charmask), "r" (longword));
  60
  61       /* Bytes that are both <= and >= are == to C.  */
  62       if (zero || (ge & le))
  63         {
  64           /* Which of the bytes was the C?  */
  65
  66           char *cp = (char *) (longword_ptr - 1);
  67           int i;
  68
  69           for (i = 0; i < 8; i++)
  70             {
  71               if (cp[i] == c)
  72                 return &cp[i];
  73               if (cp[i] == 0)
  74                 return NULL;
  75             }
  76           return NULL;
  77         }
  78     }
  79 }
  80
  81 #ifdef weak_alias
  82 #undef index
  83 weak_alias (strchr, index)
  84 #endif