diff options
| -rw-r--r-- | Misc/NEWS.d/next/Core and Builtins/2024-06-02-06-12-35.gh-issue-119879.Jit951.rst | 1 | ||||
| -rw-r--r-- | Objects/stringlib/fastsearch.h | 63 |
2 files changed, 36 insertions, 28 deletions
diff --git a/Misc/NEWS.d/next/Core and Builtins/2024-06-02-06-12-35.gh-issue-119879.Jit951.rst b/Misc/NEWS.d/next/Core and Builtins/2024-06-02-06-12-35.gh-issue-119879.Jit951.rst new file mode 100644 index 0000000..89de6b0 --- /dev/null +++ b/Misc/NEWS.d/next/Core and Builtins/2024-06-02-06-12-35.gh-issue-119879.Jit951.rst @@ -0,0 +1 @@ +String search is now slightly faster for certain cases. It now utilizes last character gap (good suffix rule) for two-way periodic needles. diff --git a/Objects/stringlib/fastsearch.h b/Objects/stringlib/fastsearch.h index 257b7bd..309ed15 100644 --- a/Objects/stringlib/fastsearch.h +++ b/Objects/stringlib/fastsearch.h @@ -256,7 +256,7 @@ STRINGLIB(_factorize)(const STRINGLIB_CHAR *needle, The local period of the cut is the minimal length of a string w such that (left endswith w or w endswith left) - and (right startswith w or w startswith left). + and (right startswith w or w startswith right). The Critical Factorization Theorem says that this maximal local period is the global period of the string. @@ -337,21 +337,20 @@ STRINGLIB(_preprocess)(const STRINGLIB_CHAR *needle, Py_ssize_t len_needle, if (p->is_periodic) { assert(p->cut <= len_needle/2); assert(p->cut < p->period); - p->gap = 0; // unused } else { // A lower bound on the period p->period = Py_MAX(p->cut, len_needle - p->cut) + 1; - // The gap between the last character and the previous - // occurrence of an equivalent character (modulo TABLE_SIZE) - p->gap = len_needle; - STRINGLIB_CHAR last = needle[len_needle - 1] & TABLE_MASK; - for (Py_ssize_t i = len_needle - 2; i >= 0; i--) { - STRINGLIB_CHAR x = needle[i] & TABLE_MASK; - if (x == last) { - p->gap = len_needle - 1 - i; - break; - } + } + // The gap between the last character and the previous + // occurrence of an equivalent character (modulo TABLE_SIZE) + p->gap = len_needle; + STRINGLIB_CHAR last = needle[len_needle - 1] & TABLE_MASK; + for (Py_ssize_t i = len_needle - 2; i >= 0; i--) { + STRINGLIB_CHAR x = needle[i] & TABLE_MASK; + if (x == last) { + p->gap = len_needle - 1 - i; + break; } } // Fill up a compressed Boyer-Moore "Bad Character" table @@ -383,6 +382,8 @@ STRINGLIB(_two_way)(const STRINGLIB_CHAR *haystack, Py_ssize_t len_haystack, const STRINGLIB_CHAR *window; LOG("===== Two-way: \"%s\" in \"%s\". =====\n", needle, haystack); + Py_ssize_t gap = p->gap; + Py_ssize_t gap_jump_end = Py_MIN(len_needle, cut + gap); if (p->is_periodic) { LOG("Needle is periodic.\n"); Py_ssize_t memory = 0; @@ -408,8 +409,16 @@ STRINGLIB(_two_way)(const STRINGLIB_CHAR *haystack, Py_ssize_t len_haystack, Py_ssize_t i = Py_MAX(cut, memory); for (; i < len_needle; i++) { if (needle[i] != window[i]) { - LOG("Right half does not match.\n"); - window_last += i - cut + 1; + if (i < gap_jump_end) { + LOG("Early right half mismatch: jump by gap.\n"); + assert(gap >= i - cut + 1); + window_last += gap; + } + else { + LOG("Late right half mismatch: jump by n (>gap)\n"); + assert(i - cut + 1 > gap); + window_last += i - cut + 1; + } memory = 0; goto periodicwindowloop; } @@ -442,10 +451,8 @@ STRINGLIB(_two_way)(const STRINGLIB_CHAR *haystack, Py_ssize_t len_haystack, } } else { - Py_ssize_t gap = p->gap; period = Py_MAX(gap, period); LOG("Needle is not periodic.\n"); - Py_ssize_t gap_jump_end = Py_MIN(len_needle, cut + gap); windowloop: while (window_last < haystack_end) { for (;;) { @@ -463,19 +470,19 @@ STRINGLIB(_two_way)(const STRINGLIB_CHAR *haystack, Py_ssize_t len_haystack, window = window_last - len_needle + 1; assert((window[len_needle - 1] & TABLE_MASK) == (needle[len_needle - 1] & TABLE_MASK)); - for (Py_ssize_t i = cut; i < gap_jump_end; i++) { - if (needle[i] != window[i]) { - LOG("Early right half mismatch: jump by gap.\n"); - assert(gap >= i - cut + 1); - window_last += gap; - goto windowloop; - } - } - for (Py_ssize_t i = gap_jump_end; i < len_needle; i++) { + Py_ssize_t i = cut; + for (; i < len_needle; i++) { if (needle[i] != window[i]) { - LOG("Late right half mismatch.\n"); - assert(i - cut + 1 > gap); - window_last += i - cut + 1; + if (i < gap_jump_end) { + LOG("Early right half mismatch: jump by gap.\n"); + assert(gap >= i - cut + 1); + window_last += gap; + } + else { + LOG("Late right half mismatch: jump by n (>gap)\n"); + assert(i - cut + 1 > gap); + window_last += i - cut + 1; + } goto windowloop; } } |