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/*
FUNCTION
<<memchr>>---search for character in memory
INDEX
memchr
ANSI_SYNOPSIS
#include <string.h>
void * memchr(const void *<[s1]>, int <[c]>, size_t <[n]>);
TRAD_SYNOPSIS
#include <string.h>
void * memchr(<[s1]>, <[c]>, <[n]>);
void *<[string]>;
int *<[c]>;
size_t *<[n]>;
DESCRIPTION
This function scans the first <[n]> bytes of the memory pointed
to by <[s1]> for the character <[c]> (converted to a char).
RETURNS
Returns a pointer to the matching byte, or a null pointer if
<[c]> does not occur in <[s1]>.
PORTABILITY
<<memchr>> is ANSI C.
<<memchr>> requires no supporting OS subroutines.
QUICKREF
memchr ansi pure
*/
#include <string.h>
#include <limits.h>
/* Nonzero if X 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))
#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
/* DETECTCHAR returns nonzero if (long)X contains the byte used
to fill (long)MASK. */
#define DETECTCHAR(X,MASK) (DETECTNULL(X ^ MASK))
void *
_DEFUN (memchr, (s1, i, n),
_CONST void *s1 _AND
int i _AND size_t n)
{
_CONST unsigned char *s = (_CONST unsigned char *)s1;
#if defined(PREFER_SIZE_OVER_SPEED) || defined(__OPTIMIZE_SIZE__)
unsigned char c = (unsigned char)i;
while (n-- > 0)
{
if (*s == c)
{
return (void *)s;
}
s++;
}
return NULL;
#else
unsigned char c = (unsigned char)i;
unsigned long mask,j;
unsigned long *aligned_addr;
if (!UNALIGNED (s))
{
mask = 0;
for (j = 0; j < LBLOCKSIZE; j++)
mask = (mask << 8) | c;
aligned_addr = (unsigned long*)s;
while ((!DETECTCHAR (*aligned_addr, mask)) && (n>LBLOCKSIZE))
{
aligned_addr++;
n -= LBLOCKSIZE;
}
/* The block of bytes currently pointed to by aligned_addr
may contain the target character or there may be less than
LBLOCKSIZE bytes left to search. We check the last few
bytes using the bytewise search. */
s = (unsigned char*)aligned_addr;
}
while (n-- > 0)
{
if (*s == c)
{
return (void *)s;
}
s++;
}
return NULL;
#endif /* not PREFER_SIZE_OVER_SPEED */
}
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