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