115 lines
2.6 KiB
C
115 lines
2.6 KiB
C
/*
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FUNCTION
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<<strncmp>>---character string compare
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INDEX
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strncmp
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SYNOPSIS
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#include <string.h>
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int strncmp(const char *<[a]>, const char * <[b]>, size_t <[length]>);
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DESCRIPTION
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<<strncmp>> compares up to <[length]> characters
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from the string at <[a]> to the string at <[b]>.
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RETURNS
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If <<*<[a]>>> sorts lexicographically after <<*<[b]>>>,
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<<strncmp>> returns a number greater than zero. If the two
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strings are equivalent, <<strncmp>> returns zero. If <<*<[a]>>>
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sorts lexicographically before <<*<[b]>>>, <<strncmp>> returns a
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number less than zero.
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PORTABILITY
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<<strncmp>> is ANSI C.
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<<strncmp>> requires no supporting OS subroutines.
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QUICKREF
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strncmp ansi pure
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*/
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#include <string.h>
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#include <limits.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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/* DETECTNULL returns nonzero if (long)X contains a NULL byte. */
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#if LONG_MAX == 2147483647L
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#define DETECTNULL(X) (((X) - 0x01010101) & ~(X) & 0x80808080)
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#else
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#if LONG_MAX == 9223372036854775807L
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#define DETECTNULL(X) (((X) - 0x0101010101010101) & ~(X) & 0x8080808080808080)
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#else
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#error long int is not a 32bit or 64bit type.
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#endif
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#endif
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#ifndef DETECTNULL
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#error long int is not a 32bit or 64bit byte
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#endif
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int
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strncmp (const char *s1,
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const char *s2,
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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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if (n == 0)
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return 0;
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while (n-- != 0 && *s1 == *s2)
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{
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if (n == 0 || *s1 == '\0')
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break;
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s1++;
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s2++;
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}
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return (*(unsigned char *) s1) - (*(unsigned char *) s2);
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#else
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unsigned long *a1;
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unsigned long *a2;
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if (n == 0)
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return 0;
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/* If s1 or s2 are unaligned, then compare bytes. */
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if (!UNALIGNED (s1, s2))
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{
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/* If s1 and s2 are word-aligned, compare them a 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 >= sizeof (long) && *a1 == *a2)
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{
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n -= sizeof (long);
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/* If we've run out of bytes or hit a null, return zero
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since we already know *a1 == *a2. */
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if (n == 0 || DETECTNULL (*a1))
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return 0;
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a1++;
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a2++;
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}
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/* A difference was detected in last few bytes of s1, so search bytewise */
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s1 = (char*)a1;
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s2 = (char*)a2;
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}
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while (n-- > 0 && *s1 == *s2)
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{
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/* If we've run out of bytes or hit a null, return zero
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since we already know *s1 == *s2. */
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if (n == 0 || *s1 == '\0')
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return 0;
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s1++;
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s2++;
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}
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return (*(unsigned char *) s1) - (*(unsigned char *) s2);
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#endif /* not PREFER_SIZE_OVER_SPEED */
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}
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