| /* |
| 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> |
| #include "_ansi.h" /* for _DEFUN */ |
| |
| /* 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 */ |
| } |