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Diffstat (limited to 'gl/memchr.c')
| -rw-r--r-- | gl/memchr.c | 201 |
1 files changed, 0 insertions, 201 deletions
diff --git a/gl/memchr.c b/gl/memchr.c deleted file mode 100644 index d44ad6de..00000000 --- a/gl/memchr.c +++ /dev/null @@ -1,201 +0,0 @@ -/* Copyright (C) 1991, 1993, 1996, 1997, 1999, 2000, 2003, 2004, 2006 Free - Software Foundation, Inc. - - Based on strlen implementation by Torbjorn Granlund (tege@sics.se), - with help from Dan Sahlin (dan@sics.se) and - commentary by Jim Blandy (jimb@ai.mit.edu); - adaptation to memchr suggested by Dick Karpinski (dick@cca.ucsf.edu), - and implemented by Roland McGrath (roland@ai.mit.edu). - -NOTE: The canonical source of this file is maintained with the GNU C Library. -Bugs can be reported to bug-glibc@prep.ai.mit.edu. - -This program is free software; you can redistribute it and/or modify it -under the terms of the GNU General Public License as published by the -Free Software Foundation; either version 2, or (at your option) any -later version. - -This program is distributed in the hope that it will be useful, -but WITHOUT ANY WARRANTY; without even the implied warranty of -MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the -GNU General Public License for more details. - -You should have received a copy of the GNU General Public License -along with this program; if not, write to the Free Software Foundation, -Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */ - -#ifndef _LIBC -# include <config.h> -#endif - -#include <string.h> - -#include <stddef.h> - -#if defined _LIBC -# include <memcopy.h> -#else -# define reg_char char -#endif - -#include <limits.h> - -#if HAVE_BP_SYM_H || defined _LIBC -# include <bp-sym.h> -#else -# define BP_SYM(sym) sym -#endif - -#undef memchr -#undef __memchr - -/* Search no more than N bytes of S for C. */ -void * -__memchr (void const *s, int c_in, size_t n) -{ - const unsigned char *char_ptr; - const unsigned long int *longword_ptr; - unsigned long int longword, magic_bits, charmask; - unsigned reg_char c; - int i; - - c = (unsigned char) c_in; - - /* Handle the first few characters by reading one character at a time. - Do this until CHAR_PTR is aligned on a longword boundary. */ - for (char_ptr = (const unsigned char *) s; - n > 0 && (size_t) char_ptr % sizeof longword != 0; - --n, ++char_ptr) - if (*char_ptr == c) - return (void *) char_ptr; - - /* All these elucidatory comments refer to 4-byte longwords, - but the theory applies equally well to any size longwords. */ - - longword_ptr = (const unsigned long int *) char_ptr; - - /* Bits 31, 24, 16, and 8 of this number are zero. Call these bits - the "holes." Note that there is a hole just to the left of - each byte, with an extra at the end: - - bits: 01111110 11111110 11111110 11111111 - bytes: AAAAAAAA BBBBBBBB CCCCCCCC DDDDDDDD - - The 1-bits make sure that carries propagate to the next 0-bit. - The 0-bits provide holes for carries to fall into. */ - - /* Set MAGIC_BITS to be this pattern of 1 and 0 bits. - Set CHARMASK to be a longword, each of whose bytes is C. */ - - magic_bits = 0xfefefefe; - charmask = c | (c << 8); - charmask |= charmask << 16; -#if 0xffffffffU < ULONG_MAX - magic_bits |= magic_bits << 32; - charmask |= charmask << 32; - if (8 < sizeof longword) - for (i = 64; i < sizeof longword * 8; i *= 2) - { - magic_bits |= magic_bits << i; - charmask |= charmask << i; - } -#endif - magic_bits = (ULONG_MAX >> 1) & (magic_bits | 1); - - /* Instead of the traditional loop which tests each character, - we will test a longword at a time. The tricky part is testing - if *any of the four* bytes in the longword in question are zero. */ - while (n >= sizeof longword) - { - /* We tentatively exit the loop if adding MAGIC_BITS to - LONGWORD fails to change any of the hole bits of LONGWORD. - - 1) Is this safe? Will it catch all the zero bytes? - Suppose there is a byte with all zeros. Any carry bits - propagating from its left will fall into the hole at its - least significant bit and stop. Since there will be no - carry from its most significant bit, the LSB of the - byte to the left will be unchanged, and the zero will be - detected. - - 2) Is this worthwhile? Will it ignore everything except - zero bytes? Suppose every byte of LONGWORD has a bit set - somewhere. There will be a carry into bit 8. If bit 8 - is set, this will carry into bit 16. If bit 8 is clear, - one of bits 9-15 must be set, so there will be a carry - into bit 16. Similarly, there will be a carry into bit - 24. If one of bits 24-30 is set, there will be a carry - into bit 31, so all of the hole bits will be changed. - - The one misfire occurs when bits 24-30 are clear and bit - 31 is set; in this case, the hole at bit 31 is not - changed. If we had access to the processor carry flag, - we could close this loophole by putting the fourth hole - at bit 32! - - So it ignores everything except 128's, when they're aligned - properly. - - 3) But wait! Aren't we looking for C, not zero? - Good point. So what we do is XOR LONGWORD with a longword, - each of whose bytes is C. This turns each byte that is C - into a zero. */ - - longword = *longword_ptr++ ^ charmask; - - /* Add MAGIC_BITS to LONGWORD. */ - if ((((longword + magic_bits) - - /* Set those bits that were unchanged by the addition. */ - ^ ~longword) - - /* Look at only the hole bits. If any of the hole bits - are unchanged, most likely one of the bytes was a - zero. */ - & ~magic_bits) != 0) - { - /* Which of the bytes was C? If none of them were, it was - a misfire; continue the search. */ - - const unsigned char *cp = (const unsigned char *) (longword_ptr - 1); - - if (cp[0] == c) - return (void *) cp; - if (cp[1] == c) - return (void *) &cp[1]; - if (cp[2] == c) - return (void *) &cp[2]; - if (cp[3] == c) - return (void *) &cp[3]; - if (4 < sizeof longword && cp[4] == c) - return (void *) &cp[4]; - if (5 < sizeof longword && cp[5] == c) - return (void *) &cp[5]; - if (6 < sizeof longword && cp[6] == c) - return (void *) &cp[6]; - if (7 < sizeof longword && cp[7] == c) - return (void *) &cp[7]; - if (8 < sizeof longword) - for (i = 8; i < sizeof longword; i++) - if (cp[i] == c) - return (void *) &cp[i]; - } - - n -= sizeof longword; - } - - char_ptr = (const unsigned char *) longword_ptr; - - while (n-- > 0) - { - if (*char_ptr == c) - return (void *) char_ptr; - else - ++char_ptr; - } - - return 0; -} -#ifdef weak_alias -weak_alias (__memchr, BP_SYM (memchr)) -#endif |