| 1 | /* |
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| 2 | FUNCTION |
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| 3 | <<memcmp>>---compare two memory areas |
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| 4 | |
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| 5 | INDEX |
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| 6 | memcmp |
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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 memcmp(const void *<[s1]>, const void *<[s2]>, size_t <[n]>); |
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| 11 | |
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| 12 | DESCRIPTION |
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| 13 | This function compares not more than <[n]> characters of the |
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| 14 | object pointed to by <[s1]> with the object pointed to by <[s2]>. |
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| 15 | |
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| 16 | |
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| 17 | RETURNS |
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| 18 | The function returns an integer greater than, equal to or |
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| 19 | less than zero according to whether the object pointed to by |
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| 20 | <[s1]> is greater than, equal to or less than the object |
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| 21 | pointed to by <[s2]>. |
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| 22 | |
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| 23 | PORTABILITY |
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| 24 | <<memcmp>> is ANSI C. |
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| 25 | |
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| 26 | <<memcmp>> requires no supporting OS subroutines. |
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| 27 | |
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| 28 | QUICKREF |
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| 29 | memcmp 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 | |
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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 | /* How many bytes are copied each iteration of the word copy loop. */ |
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| 40 | #define LBLOCKSIZE (sizeof (long)) |
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| 41 | |
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| 42 | /* Threshhold for punting to the byte copier. */ |
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| 43 | #define TOO_SMALL(LEN) ((LEN) < LBLOCKSIZE) |
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| 44 | |
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| 45 | int |
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| 46 | memcmp (const void *m1, |
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| 47 | const void *m2, |
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| 48 | size_t n) |
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| 49 | { |
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| 50 | #if defined(PREFER_SIZE_OVER_SPEED) || defined(__OPTIMIZE_SIZE__) |
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| 51 | unsigned char *s1 = (unsigned char *) m1; |
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| 52 | unsigned char *s2 = (unsigned char *) m2; |
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| 53 | |
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| 54 | while (n--) |
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| 55 | { |
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| 56 | if (*s1 != *s2) |
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| 57 | { |
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| 58 | return *s1 - *s2; |
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| 59 | } |
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| 60 | s1++; |
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| 61 | s2++; |
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| 62 | } |
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| 63 | return 0; |
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| 64 | #else |
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| 65 | unsigned char *s1 = (unsigned char *) m1; |
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| 66 | unsigned char *s2 = (unsigned char *) m2; |
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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 the size is too small, or either pointer is unaligned, |
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| 71 | then we punt to the byte compare loop. Hopefully this will |
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| 72 | not turn up in inner loops. */ |
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| 73 | if (!TOO_SMALL(n) && !UNALIGNED(s1,s2)) |
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| 74 | { |
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| 75 | /* Otherwise, load and compare the blocks of memory one |
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| 76 | word at a time. */ |
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| 77 | a1 = (unsigned long*) s1; |
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| 78 | a2 = (unsigned long*) s2; |
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| 79 | while (n >= LBLOCKSIZE) |
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| 80 | { |
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| 81 | if (*a1 != *a2) |
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| 82 | break; |
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| 83 | a1++; |
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| 84 | a2++; |
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| 85 | n -= LBLOCKSIZE; |
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| 86 | } |
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| 87 | |
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| 88 | /* check m mod LBLOCKSIZE remaining characters */ |
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| 89 | |
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| 90 | s1 = (unsigned char*)a1; |
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| 91 | s2 = (unsigned char*)a2; |
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| 92 | } |
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| 93 | |
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| 94 | while (n--) |
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| 95 | { |
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| 96 | if (*s1 != *s2) |
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| 97 | return *s1 - *s2; |
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| 98 | s1++; |
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| 99 | s2++; |
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| 100 | } |
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| 101 | |
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| 102 | return 0; |
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| 103 | #endif /* not PREFER_SIZE_OVER_SPEED */ |
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| 104 | } |
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| 105 | |
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