87 lines
2.3 KiB
C
87 lines
2.3 KiB
C
/* Copyright (C) 1992, 1993, 1994 Free Software Foundation, Inc.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Library General Public License as
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published by the Free Software Foundation; either version 2 of the
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License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Library General Public License for more details.
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You should have received a copy of the GNU Library General Public
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License along with the GNU C Library; see the file COPYING.LIB. If
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not, write to the Free Software Foundation, Inc., 675 Mass Ave,
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Cambridge, MA 02139, USA. */
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#include <string.h>
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/* Search no more than N bytes of S for C. */
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void *
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memchr (const void *s, int c, size_t n)
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{
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const char *char_ptr;
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const unsigned long int *longword_ptr;
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unsigned long int charmask;
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size_t x;
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c = (unsigned char) c;
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/* Handle the first few characters by reading one character at a time.
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Do this until STR is aligned on a 8-byte border. */
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for (char_ptr = s; n > 0 && ((unsigned long int) char_ptr & 7) != 0;
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--n, ++char_ptr)
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if (*char_ptr == c)
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return (void *) char_ptr;
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if (n == (size_t)0)
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return NULL;
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x = n;
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longword_ptr = (unsigned long int *) char_ptr;
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/* Set up a longword, each of whose bytes is C. */
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charmask = c | (c << 8);
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charmask |= charmask << 16;
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charmask |= charmask << 32;
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for (;;)
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{
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const unsigned long int longword = *longword_ptr++;
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int ge, le;
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if (x < 4)
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x = (size_t) 0;
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else
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x -= 4;
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/* Set bits in GE if bytes in CHARMASK are >= bytes in LONGWORD. */
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asm ("cmpbge %1, %2, %0" : "=r" (ge) : "r" (charmask), "r" (longword));
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/* Set bits in LE if bytes in CHARMASK are <= bytes in LONGWORD. */
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asm ("cmpbge %2, %1, %0" : "=r" (le) : "r" (charmask), "r" (longword));
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/* Bytes that are both <= and >= are == to C. */
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if (ge & le)
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{
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/* Which of the bytes was the C? */
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unsigned char *cp = (unsigned char *) (longword_ptr - 1);
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int i;
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for (i = 0; i < 6; i++)
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if (cp[i] == c)
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return &cp[i];
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return &cp[7];
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}
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if (x == (size_t)0)
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break;
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}
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return NULL;
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}
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