sysdeps/alpha/memchr.c

   1 /* Copyright (C) 1992, 1993, 1994 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 /* Search no more than N bytes of S for C.  */
  21
  22 void *
  23 memchr (const void *s, int c, size_t n)
  24 {
  25   const char *char_ptr;
  26   const unsigned long int *longword_ptr;
  27   unsigned long int charmask;
  28   size_t x;
  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 = s; n > 0 && ((unsigned long int) char_ptr & 7) != 0;
  35        --n, ++char_ptr)
  36     if (*char_ptr == c)
  37       return (void *) char_ptr;
  38
  39   if (n == (size_t)0)
  40     return NULL;
  41
  42   x = n;
  43
  44   longword_ptr = (unsigned long int *) char_ptr;
  45
  46   /* Set up a longword, each of whose bytes is C.  */
  47   charmask = c | (c << 8);
  48   charmask |= charmask << 16;
  49   charmask |= charmask << 32;
  50
  51   for (;;)
  52     {
  53       const unsigned long int longword = *longword_ptr++;
  54       int ge, le;
  55
  56       if (x < 4)
  57         x = (size_t) 0;
  58       else
  59         x -= 4;
  60
  61       /* Set bits in GE if bytes in CHARMASK are >= bytes in LONGWORD.  */
  62       asm ("cmpbge %1, %2, %0" : "=r" (ge) : "r" (charmask), "r" (longword));
  63
  64       /* Set bits in LE if bytes in CHARMASK are <= bytes in LONGWORD.  */
  65       asm ("cmpbge %2, %1, %0" : "=r" (le) : "r" (charmask), "r" (longword));
  66
  67       /* Bytes that are both <= and >= are == to C.  */
  68       if (ge & le)
  69         {
  70           /* Which of the bytes was the C?  */
  71
  72           unsigned char *cp = (unsigned char *) (longword_ptr - 1);
  73           int i;
  74
  75           for (i = 0; i < 6; i++)
  76             if (cp[i] == c)
  77               return &cp[i];
  78           return &cp[7];
  79         }
  80
  81       if (x == (size_t)0)
  82         break;
  83     }
  84
  85   return NULL;
  86 }