0,0 → 1,122 |
/* |
FUNCTION |
<<strncmp>>---character string compare |
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INDEX |
strncmp |
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ANSI_SYNOPSIS |
#include <string.h> |
int strncmp(const char *<[a]>, const char * <[b]>, size_t <[length]>); |
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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. |
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PORTABILITY |
<<strncmp>> is ANSI C. |
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<<strncmp>> requires no supporting OS subroutines. |
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QUICKREF |
strncmp ansi pure |
*/ |
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#include <string.h> |
#include <limits.h> |
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/* 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))) |
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/* 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 |
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#ifndef DETECTNULL |
#error long int is not a 32bit or 64bit byte |
#endif |
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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; |
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while (n-- != 0 && *s1 == *s2) |
{ |
if (n == 0 || *s1 == '\0') |
break; |
s1++; |
s2++; |
} |
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return (*(unsigned char *) s1) - (*(unsigned char *) s2); |
#else |
unsigned long *a1; |
unsigned long *a2; |
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if (n == 0) |
return 0; |
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/* 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); |
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/* 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++; |
} |
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/* A difference was detected in last few bytes of s1, so search bytewise */ |
s1 = (char*)a1; |
s2 = (char*)a2; |
} |
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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 */ |
} |