Details | Last modification | View Log | RSS feed
| Rev | Author | Line No. | Line |
|---|---|---|---|
| 6557 | serge | 1 | /* Byte-wise substring search, using the Two-Way algorithm. |
| 2 | * Copyright (C) 2008 Eric Blake |
||
| 3 | * Permission to use, copy, modify, and distribute this software |
||
| 4 | * is freely granted, provided that this notice is preserved. |
||
| 5 | */ |
||
| 6 | |||
| 7 | /* |
||
| 8 | FUNCTION |
||
| 9 | < |
||
| 10 | |||
| 11 | INDEX |
||
| 12 | memmem |
||
| 13 | |||
| 14 | ANSI_SYNOPSIS |
||
| 15 | #include |
||
| 16 | char *memmem(const void *<[s1]>, size_t <[l1]>, const void *<[s2]>, |
||
| 17 | size_t <[l2]>); |
||
| 18 | |||
| 19 | DESCRIPTION |
||
| 20 | |||
| 21 | Locates the first occurrence in the memory region pointed to |
||
| 22 | by <[s1]> with length <[l1]> of the sequence of bytes pointed |
||
| 23 | to by <[s2]> of length <[l2]>. If you already know the |
||
| 24 | lengths of your haystack and needle, < |
||
| 25 | faster than < |
||
| 26 | |||
| 27 | RETURNS |
||
| 28 | Returns a pointer to the located segment, or a null pointer if |
||
| 29 | <[s2]> is not found. If <[l2]> is 0, <[s1]> is returned. |
||
| 30 | |||
| 31 | PORTABILITY |
||
| 32 | < |
||
| 33 | |||
| 34 | < |
||
| 35 | |||
| 36 | QUICKREF |
||
| 37 | memmem pure |
||
| 38 | */ |
||
| 39 | |||
| 40 | #include |
||
| 41 | |||
| 42 | #if !defined(PREFER_SIZE_OVER_SPEED) && !defined(__OPTIMIZE_SIZE__) |
||
| 43 | # define RETURN_TYPE void * |
||
| 44 | # define AVAILABLE(h, h_l, j, n_l) ((j) <= (h_l) - (n_l)) |
||
| 45 | # include "str-two-way.h" |
||
| 46 | #endif |
||
| 47 | |||
| 48 | void * |
||
| 49 | _DEFUN (memmem, (haystack_start, haystack_len, needle_start, needle_len), |
||
| 50 | const void *haystack_start _AND |
||
| 51 | size_t haystack_len _AND |
||
| 52 | const void *needle_start _AND |
||
| 53 | size_t needle_len) |
||
| 54 | { |
||
| 55 | /* Abstract memory is considered to be an array of 'unsigned char' values, |
||
| 56 | not an array of 'char' values. See ISO C 99 section 6.2.6.1. */ |
||
| 57 | const unsigned char *haystack = (const unsigned char *) haystack_start; |
||
| 58 | const unsigned char *needle = (const unsigned char *) needle_start; |
||
| 59 | |||
| 60 | if (needle_len == 0) |
||
| 61 | /* The first occurrence of the empty string is deemed to occur at |
||
| 62 | the beginning of the string. */ |
||
| 63 | return (void *) haystack; |
||
| 64 | |||
| 65 | #if defined(PREFER_SIZE_OVER_SPEED) || defined(__OPTIMIZE_SIZE__) |
||
| 66 | |||
| 67 | /* Less code size, but quadratic performance in the worst case. */ |
||
| 68 | while (needle_len <= haystack_len) |
||
| 69 | { |
||
| 70 | if (!memcmp (haystack, needle, needle_len)) |
||
| 71 | return (void *) haystack; |
||
| 72 | haystack++; |
||
| 73 | haystack_len--; |
||
| 74 | } |
||
| 75 | return NULL; |
||
| 76 | |||
| 77 | #else /* compilation for speed */ |
||
| 78 | |||
| 79 | /* Larger code size, but guaranteed linear performance. */ |
||
| 80 | |||
| 81 | /* Sanity check, otherwise the loop might search through the whole |
||
| 82 | memory. */ |
||
| 83 | if (haystack_len < needle_len) |
||
| 84 | return NULL; |
||
| 85 | |||
| 86 | /* Use optimizations in memchr when possible, to reduce the search |
||
| 87 | size of haystack using a linear algorithm with a smaller |
||
| 88 | coefficient. However, avoid memchr for long needles, since we |
||
| 89 | can often achieve sublinear performance. */ |
||
| 90 | if (needle_len < LONG_NEEDLE_THRESHOLD) |
||
| 91 | { |
||
| 92 | haystack = memchr (haystack, *needle, haystack_len); |
||
| 93 | if (!haystack || needle_len == 1) |
||
| 94 | return (void *) haystack; |
||
| 95 | haystack_len -= haystack - (const unsigned char *) haystack_start; |
||
| 96 | if (haystack_len < needle_len) |
||
| 97 | return NULL; |
||
| 98 | return two_way_short_needle (haystack, haystack_len, needle, needle_len); |
||
| 99 | } |
||
| 100 | return two_way_long_needle (haystack, haystack_len, needle, needle_len); |
||
| 101 | #endif /* compilation for speed */ |
||
| 102 | } |