mirror of
https://github.com/autc04/Retro68.git
synced 2024-11-05 04:06:45 +00:00
135 lines
3.3 KiB
C
135 lines
3.3 KiB
C
/*
|
|
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, <<NUL>> 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
|
|
|
|
/* DETECTCHAR returns nonzero if (long)X contains the byte used
|
|
to fill (long)MASK. */
|
|
#define DETECTCHAR(X,MASK) (DETECTNULL(X ^ MASK))
|
|
|
|
_PTR
|
|
_DEFUN (memchr, (src_void, c, length),
|
|
_CONST _PTR src_void _AND
|
|
int c _AND
|
|
size_t length)
|
|
{
|
|
_CONST unsigned char *src = (_CONST unsigned char *) src_void;
|
|
unsigned char d = c;
|
|
|
|
#if !defined(PREFER_SIZE_OVER_SPEED) && !defined(__OPTIMIZE_SIZE__)
|
|
unsigned long *asrc;
|
|
unsigned long mask;
|
|
int i;
|
|
|
|
while (UNALIGNED (src))
|
|
{
|
|
if (!length--)
|
|
return NULL;
|
|
if (*src == d)
|
|
return (void *) src;
|
|
src++;
|
|
}
|
|
|
|
if (!TOO_SMALL (length))
|
|
{
|
|
/* If we get this far, we know that length is large and src is
|
|
word-aligned. */
|
|
/* The fast code reads the source 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 NUL in the
|
|
result. */
|
|
asrc = (unsigned long *) src;
|
|
mask = d << 8 | d;
|
|
mask = mask << 16 | mask;
|
|
for (i = 32; i < LBLOCKSIZE * 8; i <<= 1)
|
|
mask = (mask << i) | mask;
|
|
|
|
while (length >= LBLOCKSIZE)
|
|
{
|
|
if (DETECTCHAR (*asrc, mask))
|
|
break;
|
|
length -= LBLOCKSIZE;
|
|
asrc++;
|
|
}
|
|
|
|
/* If there are fewer than LBLOCKSIZE characters left,
|
|
then we resort to the bytewise loop. */
|
|
|
|
src = (unsigned char *) asrc;
|
|
}
|
|
|
|
#endif /* not PREFER_SIZE_OVER_SPEED */
|
|
|
|
while (length--)
|
|
{
|
|
if (*src == d)
|
|
return (void *) src;
|
|
src++;
|
|
}
|
|
|
|
return NULL;
|
|
}
|