Merge GDB 7.5.1

gdb/gnulib/memchr.c

-/* Copyright (C) 1991, 1993, 1996-1997, 1999-2000, 2003-2004, 2006, 2008-2011
-   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 3 of the License, or 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, see <http://www.gnu.org/licenses/>.  */
-
-#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
-#ifdef _LIBC
-# undef memchr
-#endif
-
-#ifndef weak_alias
-# define __memchr memchr
-#endif
-
-/* Search no more than N bytes of S for C.  */
-void *
-__memchr (void const *s, int c_in, size_t n)
-{
-  /* On 32-bit hardware, choosing longword to be a 32-bit unsigned
-     long instead of a 64-bit uintmax_t tends to give better
-     performance.  On 64-bit hardware, unsigned long is generally 64
-     bits already.  Change this typedef to experiment with
-     performance.  */
-  typedef unsigned long int longword;
-
-  const unsigned char *char_ptr;
-  const longword *longword_ptr;
-  longword repeated_one;
-  longword repeated_c;
-  unsigned reg_char c;
-
-  c = (unsigned char) c_in;
-
-  /* Handle the first few bytes by reading one byte 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;
-
-  longword_ptr = (const longword *) char_ptr;
-
-  /* All these elucidatory comments refer to 4-byte longwords,
-     but the theory applies equally well to any size longwords.  */
-
-  /* Compute auxiliary longword values:
-     repeated_one is a value which has a 1 in every byte.
-     repeated_c has c in every byte.  */
-  repeated_one = 0x01010101;
-  repeated_c = c | (c << 8);
-  repeated_c |= repeated_c << 16;
-  if (0xffffffffU < (longword) -1)
-    {
-      repeated_one |= repeated_one << 31 << 1;
-      repeated_c |= repeated_c << 31 << 1;
-      if (8 < sizeof (longword))
-        {
-          size_t i;
-
-          for (i = 64; i < sizeof (longword) * 8; i *= 2)
-            {
-              repeated_one |= repeated_one << i;
-              repeated_c |= repeated_c << i;
-            }
-        }
-    }
-
-  /* Instead of the traditional loop which tests each byte, 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 equal to c.  We first use an xor
-     with repeated_c.  This reduces the task to testing whether *any of the
-     four* bytes in longword1 is zero.
-
-     We compute tmp =
-       ((longword1 - repeated_one) & ~longword1) & (repeated_one << 7).
-     That is, we perform the following operations:
-       1. Subtract repeated_one.
-       2. & ~longword1.
-       3. & a mask consisting of 0x80 in every byte.
-     Consider what happens in each byte:
-       - If a byte of longword1 is zero, step 1 and 2 transform it into 0xff,
-         and step 3 transforms it into 0x80.  A carry can also be propagated
-         to more significant bytes.
-       - If a byte of longword1 is nonzero, let its lowest 1 bit be at
-         position k (0 <= k <= 7); so the lowest k bits are 0.  After step 1,
-         the byte ends in a single bit of value 0 and k bits of value 1.
-         After step 2, the result is just k bits of value 1: 2^k - 1.  After
-         step 3, the result is 0.  And no carry is produced.
-     So, if longword1 has only non-zero bytes, tmp is zero.
-     Whereas if longword1 has a zero byte, call j the position of the least
-     significant zero byte.  Then the result has a zero at positions 0, ...,
-     j-1 and a 0x80 at position j.  We cannot predict the result at the more
-     significant bytes (positions j+1..3), but it does not matter since we
-     already have a non-zero bit at position 8*j+7.
-
-     So, the test whether any byte in longword1 is zero is equivalent to
-     testing whether tmp is nonzero.  */
-
-  while (n >= sizeof (longword))
-    {
-      longword longword1 = *longword_ptr ^ repeated_c;
-
-      if ((((longword1 - repeated_one) & ~longword1)
-           & (repeated_one << 7)) != 0)
-        break;
-      longword_ptr++;
-      n -= sizeof (longword);
-    }
-
-  char_ptr = (const unsigned char *) longword_ptr;
-
-  /* At this point, we know that either n < sizeof (longword), or one of the
-     sizeof (longword) bytes starting at char_ptr is == c.  On little-endian
-     machines, we could determine the first such byte without any further
-     memory accesses, just by looking at the tmp result from the last loop
-     iteration.  But this does not work on big-endian machines.  Choose code
-     that works in both cases.  */
-
-  for (; n > 0; --n, ++char_ptr)
-    {
-      if (*char_ptr == c)
-        return (void *) char_ptr;
-    }
-
-  return NULL;
-}
-#ifdef weak_alias
-weak_alias (__memchr, BP_SYM (memchr))
-#endif