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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 */

}