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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)
{
#if defined(PREFER_SIZE_OVER_SPEED) || defined(__OPTIMIZE_SIZE__)
_CONST unsigned char *src = (_CONST unsigned char *) src_void;
c &= 0xff;
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;
c &= 0xff;
/* 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))
{
/* 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 */
}
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