| 1 | /* |
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| 2 | FUNCTION |
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| 3 | <<strcmp>>---character string compare |
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| 4 | |
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| 5 | INDEX |
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| 6 | strcmp |
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| 7 | |
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| 8 | SYNOPSIS |
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| 9 | #include <string.h> |
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| 10 | int strcmp(const char *<[a]>, const char *<[b]>); |
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| 11 | |
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| 12 | DESCRIPTION |
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| 13 | <<strcmp>> compares the string at <[a]> to |
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| 14 | the string at <[b]>. |
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| 15 | |
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| 16 | RETURNS |
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| 17 | If <<*<[a]>>> sorts lexicographically after <<*<[b]>>>, |
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| 18 | <<strcmp>> returns a number greater than zero. If the two |
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| 19 | strings match, <<strcmp>> returns zero. If <<*<[a]>>> |
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| 20 | sorts lexicographically before <<*<[b]>>>, <<strcmp>> returns a |
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| 21 | number less than zero. |
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| 22 | |
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| 23 | PORTABILITY |
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| 24 | <<strcmp>> is ANSI C. |
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| 25 | |
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| 26 | <<strcmp>> requires no supporting OS subroutines. |
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| 27 | |
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| 28 | QUICKREF |
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| 29 | strcmp ansi pure |
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| 30 | */ |
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| 31 | |
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| 32 | #include <string.h> |
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| 33 | #include <limits.h> |
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| 34 | |
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| 35 | /* Nonzero if either X or Y is not aligned on a "long" boundary. */ |
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| 36 | #define UNALIGNED(X, Y) \ |
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| 37 | (((long)X & (sizeof (long) - 1)) | ((long)Y & (sizeof (long) - 1))) |
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| 38 | |
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| 39 | /* DETECTNULL returns nonzero if (long)X contains a NULL byte. */ |
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| 40 | #if LONG_MAX == 2147483647L |
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| 41 | #define DETECTNULL(X) (((X) - 0x01010101) & ~(X) & 0x80808080) |
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| 42 | #else |
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| 43 | #if LONG_MAX == 9223372036854775807L |
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| 44 | #define DETECTNULL(X) (((X) - 0x0101010101010101) & ~(X) & 0x8080808080808080) |
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| 45 | #else |
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| 46 | #error long int is not a 32bit or 64bit type. |
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| 47 | #endif |
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| 48 | #endif |
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| 49 | |
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| 50 | #ifndef DETECTNULL |
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| 51 | #error long int is not a 32bit or 64bit byte |
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| 52 | #endif |
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| 53 | |
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| 54 | int |
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| 55 | strcmp (const char *s1, |
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| 56 | const char *s2) |
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| 57 | { |
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| 58 | #if defined(PREFER_SIZE_OVER_SPEED) || defined(__OPTIMIZE_SIZE__) |
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| 59 | while (*s1 != '\0' && *s1 == *s2) |
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| 60 | { |
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| 61 | s1++; |
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| 62 | s2++; |
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| 63 | } |
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| 64 | |
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| 65 | return (*(unsigned char *) s1) - (*(unsigned char *) s2); |
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| 66 | #else |
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| 67 | unsigned long *a1; |
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| 68 | unsigned long *a2; |
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| 69 | |
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| 70 | /* If s1 or s2 are unaligned, then compare bytes. */ |
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| 71 | if (!UNALIGNED (s1, s2)) |
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| 72 | { |
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| 73 | /* If s1 and s2 are word-aligned, compare them a word at a time. */ |
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| 74 | a1 = (unsigned long*)s1; |
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| 75 | a2 = (unsigned long*)s2; |
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| 76 | while (*a1 == *a2) |
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| 77 | { |
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| 78 | /* To get here, *a1 == *a2, thus if we find a null in *a1, |
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| 79 | then the strings must be equal, so return zero. */ |
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| 80 | if (DETECTNULL (*a1)) |
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| 81 | return 0; |
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| 82 | |
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| 83 | a1++; |
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| 84 | a2++; |
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| 85 | } |
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| 86 | |
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| 87 | /* A difference was detected in last few bytes of s1, so search bytewise */ |
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| 88 | s1 = (char*)a1; |
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| 89 | s2 = (char*)a2; |
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| 90 | } |
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| 91 | |
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| 92 | while (*s1 != '\0' && *s1 == *s2) |
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| 93 | { |
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| 94 | s1++; |
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| 95 | s2++; |
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| 96 | } |
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| 97 | return (*(unsigned char *) s1) - (*(unsigned char *) s2); |
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| 98 | #endif /* not PREFER_SIZE_OVER_SPEED */ |
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| 99 | } |
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