| Thomas Wouters | 477c8d5 | 2006-05-27 19:21:47 +0000 | [diff] [blame] | 1 | /* stringlib: fastsearch implementation */ |
| 2 | |
| 3 | #ifndef STRINGLIB_FASTSEARCH_H |
| 4 | #define STRINGLIB_FASTSEARCH_H |
| 5 | |
| 6 | /* fast search/count implementation, based on a mix between boyer- |
| 7 | moore and horspool, with a few more bells and whistles on the top. |
| Benjamin Peterson | aa06900 | 2009-01-23 03:26:36 +0000 | [diff] [blame] | 8 | for some more background, see: http://effbot.org/stringlib.htm */ |
| Thomas Wouters | 477c8d5 | 2006-05-27 19:21:47 +0000 | [diff] [blame] | 9 | |
| 10 | /* note: fastsearch may access s[n], which isn't a problem when using |
| 11 | Python's ordinary string types, but may cause problems if you're |
| 12 | using this code in other contexts. also, the count mode returns -1 |
| 13 | if there cannot possible be a match in the target string, and 0 if |
| 14 | it has actually checked for matches, but didn't find any. callers |
| 15 | beware! */ |
| 16 | |
| 17 | #define FAST_COUNT 0 |
| 18 | #define FAST_SEARCH 1 |
| 19 | |
| 20 | Py_LOCAL_INLINE(Py_ssize_t) |
| 21 | fastsearch(const STRINGLIB_CHAR* s, Py_ssize_t n, |
| 22 | const STRINGLIB_CHAR* p, Py_ssize_t m, |
| 23 | int mode) |
| 24 | { |
| 25 | long mask; |
| 26 | Py_ssize_t skip, count = 0; |
| 27 | Py_ssize_t i, j, mlast, w; |
| 28 | |
| 29 | w = n - m; |
| 30 | |
| 31 | if (w < 0) |
| 32 | return -1; |
| 33 | |
| 34 | /* look for special cases */ |
| 35 | if (m <= 1) { |
| 36 | if (m <= 0) |
| 37 | return -1; |
| 38 | /* use special case for 1-character strings */ |
| 39 | if (mode == FAST_COUNT) { |
| 40 | for (i = 0; i < n; i++) |
| 41 | if (s[i] == p[0]) |
| 42 | count++; |
| 43 | return count; |
| 44 | } else { |
| 45 | for (i = 0; i < n; i++) |
| 46 | if (s[i] == p[0]) |
| 47 | return i; |
| 48 | } |
| 49 | return -1; |
| 50 | } |
| 51 | |
| 52 | mlast = m - 1; |
| 53 | |
| 54 | /* create compressed boyer-moore delta 1 table */ |
| 55 | skip = mlast - 1; |
| 56 | /* process pattern[:-1] */ |
| 57 | for (mask = i = 0; i < mlast; i++) { |
| 58 | mask |= (1 << (p[i] & 0x1F)); |
| 59 | if (p[i] == p[mlast]) |
| 60 | skip = mlast - i - 1; |
| 61 | } |
| 62 | /* process pattern[-1] outside the loop */ |
| 63 | mask |= (1 << (p[mlast] & 0x1F)); |
| 64 | |
| 65 | for (i = 0; i <= w; i++) { |
| 66 | /* note: using mlast in the skip path slows things down on x86 */ |
| 67 | if (s[i+m-1] == p[m-1]) { |
| 68 | /* candidate match */ |
| 69 | for (j = 0; j < mlast; j++) |
| 70 | if (s[i+j] != p[j]) |
| 71 | break; |
| 72 | if (j == mlast) { |
| 73 | /* got a match! */ |
| 74 | if (mode != FAST_COUNT) |
| 75 | return i; |
| 76 | count++; |
| 77 | i = i + mlast; |
| 78 | continue; |
| 79 | } |
| 80 | /* miss: check if next character is part of pattern */ |
| 81 | if (!(mask & (1 << (s[i+m] & 0x1F)))) |
| 82 | i = i + m; |
| 83 | else |
| 84 | i = i + skip; |
| 85 | } else { |
| 86 | /* skip: check if next character is part of pattern */ |
| 87 | if (!(mask & (1 << (s[i+m] & 0x1F)))) |
| 88 | i = i + m; |
| 89 | } |
| 90 | } |
| 91 | |
| 92 | if (mode != FAST_COUNT) |
| 93 | return -1; |
| 94 | return count; |
| 95 | } |
| 96 | |
| 97 | #endif |
| 98 | |
| 99 | /* |
| 100 | Local variables: |
| 101 | c-basic-offset: 4 |
| 102 | indent-tabs-mode: nil |
| 103 | End: |
| 104 | */ |