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/*
FUNCTION
<<strncmp>>---character string compare
INDEX
strncmp
SYNOPSIS
#include <string.h>
int strncmp(const char *<[a]>, const char * <[b]>, size_t <[length]>);
DESCRIPTION
<<strncmp>> compares up to <[length]> characters
from the string at <[a]> to the string at <[b]>.
RETURNS
If <<*<[a]>>> sorts lexicographically after <<*<[b]>>>,
<<strncmp>> returns a number greater than zero. If the two
strings are equivalent, <<strncmp>> returns zero. If <<*<[a]>>>
sorts lexicographically before <<*<[b]>>>, <<strncmp>> returns a
number less than zero.
PORTABILITY
<<strncmp>> is ANSI C.
<<strncmp>> requires no supporting OS subroutines.
QUICKREF
strncmp ansi pure
*/
#include <string.h>
#include <limits.h>
/* Nonzero if either X or Y is not aligned on a "long" boundary. */
#define UNALIGNED(X, Y) \
(((long)X & (sizeof (long) - 1)) | ((long)Y & (sizeof (long) - 1)))
/* DETECTNULL returns nonzero if (long)X contains a NULL byte. */
#if LONG_MAX == 2147483647L
#define DETECTNULL(X) (((X) - 0x01010101) & ~(X) & 0x80808080)
#else
#if LONG_MAX == 9223372036854775807L
#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
int
_DEFUN (strncmp, (s1, s2, n),
const char *s1,
const char *s2,
size_t n)
{
#if defined(PREFER_SIZE_OVER_SPEED) || defined(__OPTIMIZE_SIZE__)
if (n == 0)
return 0;
while (n-- != 0 && *s1 == *s2)
{
if (n == 0 || *s1 == '\0')
break;
s1++;
s2++;
}
return (*(unsigned char *) s1) - (*(unsigned char *) s2);
#else
unsigned long *a1;
unsigned long *a2;
if (n == 0)
return 0;
/* If s1 or s2 are unaligned, then compare bytes. */
if (!UNALIGNED (s1, s2))
{
/* If s1 and s2 are word-aligned, compare them a word at a time. */
a1 = (unsigned long*)s1;
a2 = (unsigned long*)s2;
while (n >= sizeof (long) && *a1 == *a2)
{
n -= sizeof (long);
/* If we've run out of bytes or hit a null, return zero
since we already know *a1 == *a2. */
if (n == 0 || DETECTNULL (*a1))
return 0;
a1++;
a2++;
}
/* A difference was detected in last few bytes of s1, so search bytewise */
s1 = (char*)a1;
s2 = (char*)a2;
}
while (n-- > 0 && *s1 == *s2)
{
/* If we've run out of bytes or hit a null, return zero
since we already know *s1 == *s2. */
if (n == 0 || *s1 == '\0')
return 0;
s1++;
s2++;
}
return (*(unsigned char *) s1) - (*(unsigned char *) s2);
#endif /* not PREFER_SIZE_OVER_SPEED */
}
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