summaryrefslogtreecommitdiff
path: root/lib/memrchr.c
diff options
context:
space:
mode:
authorPaul Eggert <eggert@cs.ucla.edu>2006-08-21 07:26:38 +0000
committerPaul Eggert <eggert@cs.ucla.edu>2006-08-21 07:26:38 +0000
commit0f7a044109b860443ecaa4f8a37652b1b4423057 (patch)
treeb5834ed9867213221a2636e0fa7e8da178749a76 /lib/memrchr.c
parent11fd62b0080ce376b26241bd789b7e7390befef6 (diff)
downloadcoreutils-0f7a044109b860443ecaa4f8a37652b1b4423057.tar.xz
Remove from CVS, since the bootstrap script generates them automatically.
Diffstat (limited to 'lib/memrchr.c')
-rw-r--r--lib/memrchr.c194
1 files changed, 0 insertions, 194 deletions
diff --git a/lib/memrchr.c b/lib/memrchr.c
deleted file mode 100644
index 0b6659fd9..000000000
--- a/lib/memrchr.c
+++ /dev/null
@@ -1,194 +0,0 @@
-/* memrchr -- find the last occurrence of a byte in a memory block
-
- Copyright (C) 1991, 1993, 1996, 1997, 1999, 2000, 2003, 2004, 2005
- 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).
-
- 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. */
-
-#ifdef HAVE_CONFIG_H
-# include <config.h>
-#endif
-
-#if defined _LIBC
-# include <string.h>
-# include <memcopy.h>
-#else
-# include "memrchr.h"
-# define reg_char char
-#endif
-
-#include <limits.h>
-
-#undef __memrchr
-#undef memrchr
-
-#ifndef weak_alias
-# define __memrchr memrchr
-#endif
-
-/* Search no more than N bytes of S for C. */
-void *
-__memrchr (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 last 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;
- n > 0 && (size_t) char_ptr % sizeof longword != 0;
- --n)
- 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;
-
- if (8 < sizeof longword)
- for (i = sizeof longword - 1; 8 <= i; i--)
- if (cp[i] == c)
- return (void *) &cp[i];
- if (7 < sizeof longword && cp[7] == c)
- return (void *) &cp[7];
- if (6 < sizeof longword && cp[6] == c)
- return (void *) &cp[6];
- if (5 < sizeof longword && cp[5] == c)
- return (void *) &cp[5];
- if (4 < sizeof longword && cp[4] == c)
- return (void *) &cp[4];
- if (cp[3] == c)
- return (void *) &cp[3];
- if (cp[2] == c)
- return (void *) &cp[2];
- if (cp[1] == c)
- return (void *) &cp[1];
- if (cp[0] == c)
- return (void *) cp;
- }
-
- n -= sizeof longword;
- }
-
- char_ptr = (const unsigned char *) longword_ptr;
-
- while (n-- > 0)
- {
- if (*--char_ptr == c)
- return (void *) char_ptr;
- }
-
- return 0;
-}
-#ifdef weak_alias
-weak_alias (__memrchr, memrchr)
-#endif