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/*
FUNCTION
	<<memchr>>---find character in memory
 
INDEX
	memchr
 
ANSI_SYNOPSIS
	#include <string.h>
	void *memchr(const void *<[src]>, int <[c]>, size_t <[length]>);
 
TRAD_SYNOPSIS
	#include <string.h>
	void *memchr(<[src]>, <[c]>, <[length]>)
	void *<[src]>;
	void *<[c]>;
	size_t <[length]>;
 
DESCRIPTION
	This function searches memory starting at <<*<[src]>>> for the
	character <[c]>.  The search only ends with the first
	occurrence of <[c]>, or after <[length]> characters; in
	particular, <<NULL>> does not terminate the search.
 
RETURNS
	If the character <[c]> is found within <[length]> characters
	of <<*<[src]>>>, a pointer to the character is returned. If
	<[c]> is not found, then <<NULL>> is returned.
 
PORTABILITY
<<memchr>>> is ANSI C.
 
<<memchr>>  requires no supporting OS subroutines.
 
QUICKREF
	memchr ansi pure
*/
 
#include <_ansi.h>
#include <string.h>
#include <limits.h>
 
/* Nonzero if either X or Y is not aligned on a "long" boundary.  */
#define UNALIGNED(X) ((long)X & (sizeof (long) - 1))
 
/* How many bytes are loaded each iteration of the word copy loop.  */
#define LBLOCKSIZE (sizeof (long))
 
/* Threshhold for punting to the bytewise iterator.  */
#define TOO_SMALL(LEN)  ((LEN) < LBLOCKSIZE)
 
#if LONG_MAX == 2147483647L
#define DETECTNULL(X) (((X) - 0x01010101) & ~(X) & 0x80808080)
#else
#if LONG_MAX == 9223372036854775807L
/* Nonzero if X (a long int) contains a NULL byte. */
#define DETECTNULL(X) (((X) - 0x0101010101010101) & ~(X) & 0x8080808080808080)
#else
#error long int is not a 32bit or 64bit type.
#endif
#endif
 
#ifndef DETECTNULL
#error long int is not a 32bit or 64bit byte
#endif
 
 
_PTR
_DEFUN (memchr, (src_void, c, length),
	_CONST _PTR src_void _AND
	int c _AND
	size_t length)
{
#ifdef PREFER_SIZE_OVER_SPEED
  _CONST unsigned char *src = (_CONST unsigned char *) src_void;
 
  while (length--)
    {
      if (*src == c)
	return (char *) src;
      src++;
    }
  return NULL;
#else
  _CONST unsigned char *src = (_CONST unsigned char *) src_void;
  unsigned long *asrc;
  unsigned long  buffer;
  unsigned long  mask;
  int i, j;
 
  /* If the size is small, or src is unaligned, then 
     use the bytewise loop.  We can hope this is rare.  */
  if (TOO_SMALL (length) || UNALIGNED (src)) 
    {
      while (length--)
        {
          if (*src == c)
	    return (char *) src;
          src++;
        }
      return NULL;
    }
 
  /* The fast code reads the ASCII one word at a time and only 
     performs the bytewise search on word-sized segments if they
     contain the search character, which is detected by XORing 
     the word-sized segment with a word-sized block of the search
     character and then detecting for the presence of NULL in the
     result.  */
  asrc = (unsigned long*) src;
  mask = 0;
  for (i = 0; i < LBLOCKSIZE; i++)
    mask = (mask << 8) + c;
 
  while (length > LBLOCKSIZE)
    {
      buffer = *asrc;
      buffer ^=  mask;
      if (DETECTNULL (buffer))
	{
          src = (unsigned char*) asrc;
  	  for ( j = 0; j < LBLOCKSIZE; j++ )
	    {
              if (*src == c)
                return (char*) src;
              src++;
	    }
	}
      length -= LBLOCKSIZE;
      asrc++;
    }
 
  /* If there are fewer than LBLOCKSIZE characters left,
     then we resort to the bytewise loop.  */
 
  src = (unsigned char*) asrc;
  while (length--)
   {
      if (*src == c)
        return (char*) src;
      src++;
   } 
 
  return NULL;
#endif /* not PREFER_SIZE_OVER_SPEED */
}