source: vendor/diffutils/2.8.1/lib/memchr.c@ 2662

/* Copyright (C) 1991,93,96,97,99,2000 Free Software Foundation, Inc.
   Based on strlen implementation by Torbjorn Granlund ([email protected]),
   with help from Dan Sahlin ([email protected]) and
   commentary by Jim Blandy ([email protected]);
   adaptation to memchr suggested by Dick Karpinski ([email protected]),
   and implemented by Roland McGrath ([email protected]).

NOTE: The canonical source of this file is maintained with the GNU C Library.
Bugs can be reported to [email protected].

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., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
USA.  */

#ifdef HAVE_CONFIG_H
# include <config.h>
#endif

#undef __ptr_t
#if defined (__cplusplus) || (defined (__STDC__) && __STDC__)
# define __ptr_t void *
#else /* Not C++ or ANSI C.  */
# define __ptr_t char *
#endif /* C++ or ANSI C.  */

#if defined _LIBC
# include <string.h>
# include <memcopy.h>
#else
# define reg_char char
#endif

#if HAVE_STDLIB_H || defined _LIBC
# include <stdlib.h>
#endif

#if HAVE_LIMITS_H || defined _LIBC
# include <limits.h>
#endif

#define LONG_MAX_32_BITS 2147483647

#ifndef LONG_MAX
# define LONG_MAX LONG_MAX_32_BITS
#endif

#include <sys/types.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.  */
__ptr_t
__memchr (s, c_in, n)
     const __ptr_t 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;

  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 && ((unsigned long int) char_ptr
                 & (sizeof (longword) - 1)) != 0;
       --n, ++char_ptr)
    if (*char_ptr == c)
      return (__ptr_t) char_ptr;

  /* All these elucidatory comments refer to 4-byte longwords,
     but the theory applies equally well to 8-byte longwords.  */

  longword_ptr = (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.  */

  if (sizeof (longword) != 4 && sizeof (longword) != 8)
    abort ();

#if LONG_MAX <= LONG_MAX_32_BITS
  magic_bits = 0x7efefeff;
#else
  magic_bits = ((unsigned long int) 0x7efefefe << 32) | 0xfefefeff;
#endif

  /* Set up a longword, each of whose bytes is C.  */
  charmask = c | (c << 8);
  charmask |= charmask << 16;
#if LONG_MAX > LONG_MAX_32_BITS
  charmask |= charmask << 32;
#endif