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86 lines
2.6 KiB
C
86 lines
2.6 KiB
C
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/* Copyright (C) 1992 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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/* Return the length of the null-terminated string STR. Scan for
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the null terminator quickly by testing eight bytes at a time. */
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char *
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strchr (const char *str, int c)
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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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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 = str; ((unsigned long int) char_ptr & 7) != 0; ++char_ptr)
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if (*char_ptr == '\0')
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return NULL;
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else if (*char_ptr == c)
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return char_ptr;
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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, zero;
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/* Set bits in ZERO if bytes in LONGWORD are zero. */
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asm ("cmpbge $31, %1, %0" : "=r" (zero) : "r" (longword));
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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 (zero || (ge & le))
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{
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/* Which of the bytes was the C? */
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const char *cp = (const char *) (longword_ptr - 1);
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if (cp[0] == c)
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return cp;
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if (cp[0] == 0)
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return NULL;
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if (cp[1] == c)
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return &cp[1];
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if (cp[1] == 0)
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return NULL;
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if (cp[2] == c)
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return &cp[2];
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if (cp[2] == 0)
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return NULL;
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if (cp[3] == c)
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return &cp[3];
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return NULL;
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}
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}
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}
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