123 lines
2.8 KiB
C
123 lines
2.8 KiB
C
/*
|
|
FUNCTION
|
|
<<strncmp>>---character string compare
|
|
|
|
INDEX
|
|
strncmp
|
|
|
|
ANSI_SYNOPSIS
|
|
#include <string.h>
|
|
int strncmp(const char *<[a]>, const char * <[b]>, size_t <[length]>);
|
|
|
|
TRAD_SYNOPSIS
|
|
#include <string.h>
|
|
int strncmp(<[a]>, <[b]>, <[length]>)
|
|
char *<[a]>;
|
|
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 _AND
|
|
_CONST char *s2 _AND
|
|
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 */
|
|
}
|