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/* |
FUNCTION |
<<memcmp>>---compare two memory areas |
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INDEX |
memcmp |
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ANSI_SYNOPSIS |
#include <string.h> |
int memcmp(const void *<[s1]>, const void *<[s2]>, size_t <[n]>); |
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TRAD_SYNOPSIS |
#include <string.h> |
int memcmp(<[s1]>, <[s2]>, <[n]>) |
void *<[s1]>; |
void *<[s2]>; |
size_t <[n]>; |
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DESCRIPTION |
This function compares not more than <[n]> characters of the |
object pointed to by <[s1]> with the object pointed to by <[s2]>. |
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RETURNS |
The function returns an integer greater than, equal to or |
less than zero according to whether the object pointed to by |
<[s1]> is greater than, equal to or less than the object |
pointed to by <[s2]>. |
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PORTABILITY |
<<memcmp>> is ANSI C. |
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<<memcmp>> requires no supporting OS subroutines. |
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QUICKREF |
memcmp ansi pure |
*/ |
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#include <string.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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/* How many bytes are copied each iteration of the word copy loop. */ |
#define LBLOCKSIZE (sizeof (long)) |
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/* Threshhold for punting to the byte copier. */ |
#define TOO_SMALL(LEN) ((LEN) < LBLOCKSIZE) |
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int |
_DEFUN (memcmp, (m1, m2, n), |
_CONST _PTR m1 _AND |
_CONST _PTR m2 _AND |
size_t n) |
{ |
#if defined(PREFER_SIZE_OVER_SPEED) || defined(__OPTIMIZE_SIZE__) |
unsigned char *s1 = (unsigned char *) m1; |
unsigned char *s2 = (unsigned char *) m2; |
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while (n--) |
{ |
if (*s1 != *s2) |
{ |
return *s1 - *s2; |
} |
s1++; |
s2++; |
} |
return 0; |
#else |
unsigned char *s1 = (unsigned char *) m1; |
unsigned char *s2 = (unsigned char *) m2; |
unsigned long *a1; |
unsigned long *a2; |
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/* If the size is too small, or either pointer is unaligned, |
then we punt to the byte compare loop. Hopefully this will |
not turn up in inner loops. */ |
if (!TOO_SMALL(n) && !UNALIGNED(s1,s2)) |
{ |
/* Otherwise, load and compare the blocks of memory one |
word at a time. */ |
a1 = (unsigned long*) s1; |
a2 = (unsigned long*) s2; |
while (n >= LBLOCKSIZE) |
{ |
if (*a1 != *a2) |
break; |
a1++; |
a2++; |
n -= LBLOCKSIZE; |
} |
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/* check m mod LBLOCKSIZE remaining characters */ |
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s1 = (unsigned char*)a1; |
s2 = (unsigned char*)a2; |
} |
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while (n--) |
{ |
if (*s1 != *s2) |
return *s1 - *s2; |
s1++; |
s2++; |
} |
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return 0; |
#endif /* not PREFER_SIZE_OVER_SPEED */ |
} |
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