/* 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 */ }