Refactor subsequence matcher to not use recursion and support multithreading. Also add a python implementation for easy experimentation with the algorithm.

src/calibre/gui2/tweak_book/matcher.c

@@ -17,12 +17,8 @@
 #ifdef _MSC_VER
 // inline does not work with the visual studio C compiler
 #define inline
-#define qsort qsort_s
-#else
-#define qsort qsort_r
 #endif
 
-
 typedef unsigned char bool;
 #define TRUE 1
 #define FALSE 0
@@ -31,132 +27,224 @@ typedef unsigned char bool;
 #define nullfree(x) if(x != NULL) free(x); x = NULL;
 
 // Algorithm to sort items by subsequence score {{{
+typedef struct {
+    double score;
+    int32_t *positions;
+} MemoryItem;
+
+static MemoryItem*** alloc_memory(int32_t needle_len, int32_t max_haystack_len) {
+    MemoryItem ***ans = NULL, **d1 = NULL, *d2 = NULL;
+    size_t num = max_haystack_len * max_haystack_len * needle_len;
+    size_t position_sz = needle_len * sizeof(int32_t);
+    size_t sz = (num * (sizeof(MemoryItem) + position_sz)) + (max_haystack_len * sizeof(MemoryItem**)) + (needle_len * sizeof(MemoryItem*));
+    int32_t hidx, nidx, last_idx, i, j;
+    char *base = NULL;
+
+    ans = (MemoryItem***) calloc(sz, 1);
+    if (ans != NULL) {
+        d1 = (MemoryItem**)(ans + max_haystack_len);
+        d2 = (MemoryItem*) (d1 + max_haystack_len * needle_len );
+        for (i = 0; i < max_haystack_len; i++) {
+            ans[i] = d1 + i * needle_len;
+            for (j = 0; j < needle_len; j++) d1[i*needle_len + j] = d2 + j;
+        }
+
+        base = ((char*)ans) + (sizeof(MemoryItem**)*max_haystack_len) + (sizeof(MemoryItem*)*needle_len) + (sizeof(MemoryItem)*max_haystack_len);
+
+        for (hidx = 0; hidx < max_haystack_len; hidx++) {
+            for (nidx = 0; nidx < needle_len; nidx++) {
+                for (last_idx = 0; last_idx < max_haystack_len; last_idx++) {
+                    ans[hidx][nidx][last_idx].positions = (int32_t*)base;
+                    base += position_sz;
+                }
+            }
+        }
+    }
+    return ans;
+}
+
+static void clear_memory(MemoryItem ***mem, int32_t needle_len, int32_t max_haystack_len) {
+    int32_t hidx, nidx, last_idx;
+    for (hidx = 0; hidx < max_haystack_len; hidx++) {
+        for (nidx = 0; nidx < needle_len; nidx++) {
+            for (last_idx = 0; last_idx < max_haystack_len; last_idx++) {
+                mem[hidx][nidx][last_idx].score = DBL_MAX;
+            }
+        }
+    }
+}
+
+typedef struct {
+    int32_t hidx;
+    int32_t nidx;
+    int32_t last_idx;
+    double score;
+    int32_t *positions;
+} StackItem;
+
+typedef struct {
+    ssize_t pos;
+    int32_t needle_len;
+    size_t size;
+    StackItem *items;
+} Stack;
+
+static void alloc_stack(Stack *stack, int32_t needle_len, int32_t max_haystack_len) {
+    StackItem *ans = NULL;
+    char *base = NULL;
+    size_t num = max_haystack_len * needle_len;
+    size_t position_sz = needle_len * sizeof(int32_t);
+    size_t sz = sizeof(StackItem) + position_sz;
+    size_t i = 0;
+
+    stack->needle_len = needle_len;
+    stack->pos = -1;
+    stack->size = num;
+    ans = (StackItem*) calloc(num, sz);
+    if (ans != NULL) {
+        base = (char*)(ans + num);
+        for (i = 0; i < num; i++, base += position_sz) ans[i].positions = (int32_t*) base;
+        stack->items = ans;
+    }
+}
+
+static void stack_clear(Stack *stack) { stack->pos = -1; }
+
+static void stack_push(Stack *stack, int32_t hidx, int32_t nidx, int32_t last_idx, double score, int32_t *positions) {
+    StackItem *si = &(stack->items[++stack->pos]);
+    si->hidx = hidx; si->nidx = nidx; si->last_idx = last_idx; si->score = score;
+    memcpy(si->positions, positions, sizeof(*positions) * stack->needle_len);
+}
+
+static void stack_pop(Stack *stack, int32_t *hidx, int32_t *nidx, int32_t *last_idx, double *score, int32_t *positions) {
+    StackItem *si = &(stack->items[stack->pos--]);
+    *hidx = si->hidx; *nidx = si->nidx; *last_idx = si->last_idx; *score = si->score;
+    memcpy(positions, si->positions, sizeof(*positions) * stack->needle_len);
+}
+
 typedef struct {
     UChar *haystack;
     int32_t haystack_len;
     UChar *needle;
     int32_t needle_len;
     double max_score_per_char;
-    double **memo;
+    MemoryItem ***memo;
     UChar *level1;
     UChar *level2;
     UChar *level3;
 } MatchInfo;
 
 typedef struct {
-    UChar *item;
-    char *sort_key;
-    uint32_t sort_key_len;
-    PyObject *py_item;
     double score;
+    int32_t *positions;
 } Match;
 
-static double recursive_match(MatchInfo *m, int32_t haystack_idx, int32_t needle_idx, int32_t last_idx, double score) {
-    double seen_score = 0.0, memoized = DBL_MAX, score_for_char, factor, sub_score; 
-    int32_t i = 0, j = 0, distance, curri;
-    UChar32 c, d, last;
-    bool found;
 
-    // do we have a memoized result we can return?
-    memoized = m->memo[needle_idx][haystack_idx];
-    if (memoized != DBL_MAX)
-        return memoized;
+static double calc_score_for_char(MatchInfo *m, UChar32 last, UChar32 current, int32_t distance_from_last_match) {
+    double factor = 1.0;
+    double ans = m->max_score_per_char;
 
-    // bail early if not enough room (left) in haystack for (rest of) needle
-    if (m->haystack_len - haystack_idx < m->needle_len - needle_idx) {
-        score = 0.0;
-        goto memoize;
+    if (u_strchr32(m->level1, last) != NULL)
+        factor = 0.9;
+    else if (u_strchr32(m->level2, last) != NULL)
+        factor = 0.8;
+    else if (u_isULowercase(last) && u_isUUppercase(current))
+        factor = 0.8;  // CamelCase
+    else if (u_strchr32(m->level3, last) != NULL)
+        factor = 0.7;
+    else
+        // If last is not a special char, factor diminishes
+        // as distance from last matched char increases
+        factor = (1.0 / distance_from_last_match) * 0.75;
+    return ans * factor;
+}
+
+static void convert_positions(int32_t *positions, int32_t *final_positions, UChar *string, int32_t char_len, int32_t byte_len, double score) {
+    // The positions array stores character positions as byte offsets in string, convert them into character offsets
+    int32_t i, *end;
+
+    if (score == 0.0) {
+        for (i = 0; i < char_len; i++) final_positions[i] = -1;
+        return;
     }
-    for (i = needle_idx; i < m->needle_len; ) {
-        curri = i;
-        U16_NEXT(m->needle, i, m->needle_len, c);  // i now points to the next codepoint
-        found = FALSE;
 
-        // similar to above, we'll stop iterating when we know we're too close
-        // to the end of the string to possibly match
-        for (j = haystack_idx; j <= m->haystack_len - (m->needle_len - curri); ) {
-            haystack_idx = j;
-            U16_NEXT(m->haystack, j, m->haystack_len, d);  // j now points to the next codepoint
+    end = final_positions + char_len;
+    for (i = 0; i < byte_len && final_positions < end; i++) {
+        if (positions[i] == -1) continue;
+        *final_positions = u_countChar32(string, positions[i]);
+        final_positions += 1;
+    }
+}
 
-            if (u_foldCase(c, U_FOLD_CASE_DEFAULT) == u_foldCase(d, U_FOLD_CASE_DEFAULT)) {
-                found = TRUE;
+static double process_item(MatchInfo *m, Stack *stack, int32_t *final_positions) {
+    UChar32 nc, hc, lc;
+    UChar *p;
+    double final_score = 0.0, score = 0.0, score_for_char = 0.0;
+    int32_t pos, i, j, hidx, nidx, last_idx, distance, *positions = final_positions + m->needle_len;
+    stack_push(stack, 0, 0, 0, 0.0, final_positions);
+    MemoryItem mem = {0};
 
-                // calculate score
-                score_for_char = m->max_score_per_char;
-                distance = haystack_idx - last_idx;
-
-                if (distance > 1) {
-                    factor = 1.0;
-                    U16_GET(m->haystack, haystack_idx - 1, haystack_idx - 1, m->haystack_len, last);
-                    if (u_strchr32(m->level1, last))
-                        factor = 0.9;
-                    else if (u_strchr32(m->level2, last))
-                        factor = 0.8;
-                    else if (u_isULowercase(last) && u_isUUppercase(d))
-                        factor = 0.8;  // CamelCase
-                    else if (u_strchr32(m->level3, last))
-                        factor = 0.7;
-                    else
-                        // if no "special" chars behind char, factor diminishes
-                        // as distance from last matched char increases
-                        factor = (1.0 / distance) * 0.75;
-                    score_for_char *= factor;
-                }
-
-                if (j < m->haystack_len) {
-                    // bump cursor one char to the right and
-                    // use recursion to try and find a better match
-                    sub_score = recursive_match(m, j, curri, last_idx, score);
-                    if (sub_score > seen_score)
-                        seen_score = sub_score;
+    while (stack->pos >= 0) {
+        stack_pop(stack, &hidx, &nidx, &last_idx, &score, positions);
+        mem = m->memo[hidx][nidx][last_idx];
+        if (mem.score == DBL_MAX) {
+            // No memoized result, calculate the score
+            for (i = nidx; i < m->needle_len;) {
+                nidx = i;
+                U16_NEXT(m->needle, i, m->needle_len, nc); // i now points to next char in needle 
+                if (m->haystack_len - hidx < m->needle_len - nidx) { score = 0.0; break; }
+                p = u_strchr32(m->haystack + hidx, nc);  // TODO: Use primary collation for the find
+                if (p == NULL) { score = 0.0; break; }
+                pos = p - m->haystack;
+                distance = u_countChar32(m->haystack + last_idx, pos - last_idx);  
+                if (distance <= 1) score_for_char = m->max_score_per_char;
+                else {
+                    U16_GET(m->haystack, 0, pos, m->haystack_len, hc); 
+                    j = pos;
+                    U16_PREV(m->haystack, 0, j, lc); // lc is the prev character
+                    score_for_char = calc_score_for_char(m, lc, hc, distance);
                 }
+                j = pos;
+                U16_NEXT(m->haystack, j, m->haystack_len, hc); 
+                hidx = j;
+                if (m->haystack_len - hidx >= m->needle_len - nidx) stack_push(stack, hidx, nidx, last_idx, score, positions);
+                last_idx = pos; 
+                positions[nidx] = pos; 
                 score += score_for_char;
-                last_idx = haystack_idx + 1;
-                break;
-            }
-        } // for(j)
+            } // for(i) iterate over needle
+            mem.score = score; memcpy(mem.positions, positions, sizeof(*positions) * m->needle_len);
 
-        if (!found) {
-            score = 0.0;
-            goto memoize;
+        } else {
+            score = mem.score; memcpy(positions, mem.positions, sizeof(*positions) * m->needle_len);
+        }
+        // We have calculated the score for this hidx, nidx, last_idx combination, update final_score and final_positions, if needed
+        if (score > final_score) {
+            final_score = score;
+            memcpy(final_positions, positions, sizeof(*positions) * m->needle_len);
         }
     }
-
-    score = score > seen_score ? score : seen_score;
-
-memoize:
-    m->memo[needle_idx][haystack_idx] = score;
-    return score;
+    return final_score;
 }
 
-static double** alloc_memo(size_t rows, size_t cols) {
-    double **array, *data; /* Declare this first so we can use it with sizeof. */
-    size_t i;
-    const size_t row_pointers_bytes = rows * sizeof(*array);
-    const size_t row_elements_bytes = cols * sizeof(**array);
-    array = malloc(row_pointers_bytes + rows * row_elements_bytes);
-    if (array != NULL) {
-        data = (double*)(array + rows);
-        for(i = 0; i < rows; i++) array[i] = data + i * cols;
-    }
-    return array;
-}
 
-static bool match(UChar **items, int32_t *item_lengths, uint32_t item_count, UChar *needle, int32_t needle_len, Match *match_results, UChar *level1, UChar *level2, UChar *level3) {
-    uint32_t i = 0, maxhl = 0; 
-    int32_t r = 0, c = 0;
+static bool match(UChar **items, int32_t *item_lengths, uint32_t item_count, UChar *needle, Match *match_results, int32_t *final_positions, int32_t needle_char_len, UChar *level1, UChar *level2, UChar *level3) {
+    Stack stack = {0};
+    int32_t i = 0, maxhl = 0; 
+    int32_t r = 0, *positions = NULL;
     MatchInfo *matches = NULL;
     bool ok = FALSE;
-    double **memo = NULL;
+    MemoryItem ***memo = NULL;
+    int32_t needle_len = u_strlen(needle);
 
-    if (needle_len == 0) {
+    if (needle_len <= 0 || item_count <= 0) {
         for (i = 0; i < item_count; i++) match_results[i].score = 0.0;
         ok = TRUE;
         goto end;
     }
 
     matches = (MatchInfo*)calloc(item_count, sizeof(MatchInfo));
-    if (matches == NULL) goto end;
+    positions = (int32_t*)calloc(2*needle_len, sizeof(int32_t)); // One set of positions is the final answer and one set is working space
+    if (matches == NULL || positions == NULL) {PyErr_NoMemory(); goto end;}
 
     for (i = 0; i < item_count; i++) {
         matches[i].haystack = items[i];
@@ -170,36 +258,36 @@ static bool match(UChar **items, int32_t *item_lengths, uint32_t item_count, UCh
         maxhl = MAX(maxhl, matches[i].haystack_len);
     }
 
-    memo = alloc_memo(needle_len, maxhl);
-    if (memo == NULL) {PyErr_NoMemory(); goto end;}
+    if (maxhl <= 0) {
+        for (i = 0; i < item_count; i++) match_results[i].score = 0.0;
+        ok = TRUE;
+        goto end;
+    }
+
+    alloc_stack(&stack, needle_len, maxhl);
+    memo = alloc_memory(needle_len, maxhl);
+    if (stack.items == NULL || memo == NULL) {PyErr_NoMemory(); goto end;}
 
     for (i = 0; i < item_count; i++) {
         for (r = 0; r < needle_len; r++) {
-            for (c = 0; c < maxhl; c++) memo[r][c] = DBL_MAX;
+            positions[r] = -1;
         }
+        stack_clear(&stack);
+        clear_memory(memo, needle_len, matches[i].haystack_len);
         matches[i].memo = memo;
-        match_results[i].score = recursive_match(&matches[i], 0, 0, 0, 0.0);
+        match_results[i].score = process_item(&matches[i], &stack, positions);
+        convert_positions(positions, final_positions + i, matches[i].haystack, needle_char_len, needle_len, match_results[i].score);
     }
 
     ok = TRUE;
 end:
+    nullfree(positions);
+    nullfree(stack.items);
     nullfree(matches);
     nullfree(memo);
     return ok;
 }
 
-int cmp_score(const void *a, const void *b, void *arg)
-{
-    Match a_match = *(Match *)a;
-    Match b_match = *(Match *)b;
-
-    if (a_match.score > b_match.score)
-        return -1; // a scores higher, a should appear sooner
-    else if (a_match.score < b_match.score)
-        return 1; // b scores higher, a should appear later
-    else
-        return strncmp(a_match.sort_key, b_match.sort_key, MIN(a_match.sort_key_len, b_match.sort_key_len));
-}
 // }}}
 
 // Matcher object definition {{{
@@ -207,17 +295,14 @@ typedef struct {
     PyObject_HEAD
     // Type-specific fields go here.
     UChar **items;
-    char **sort_items;
     uint32_t item_count;
     int32_t *item_lengths;
-    int32_t *sort_item_lengths;
-    PyObject *py_items;
-    PyObject *py_sort_keys;
     UChar *level1;
     UChar *level2;
     UChar *level3;
 
 } Matcher;
+
 // Matcher.__init__() {{{
 
 static void free_matcher(Matcher *self) {
@@ -225,7 +310,7 @@ static void free_matcher(Matcher *self) {
     if (self->items != NULL) {
         for (i = 0; i < self->item_count; i++) { nullfree(self->items[i]); }
     }
-    nullfree(self->items); nullfree(self->sort_items); nullfree(self->item_lengths); nullfree(self->sort_item_lengths); Py_XDECREF(self->py_items); Py_XDECREF(self->py_sort_keys); 
+    nullfree(self->items); nullfree(self->item_lengths); 
     nullfree(self->level1); nullfree(self->level2); nullfree(self->level3);
 }
 static void
@@ -239,66 +324,60 @@ Matcher_dealloc(Matcher* self)
 static int
 Matcher_init(Matcher *self, PyObject *args, PyObject *kwds)
 {
-    PyObject *items = NULL, *sort_keys = NULL, *p = NULL;
+    PyObject *items = NULL, *p = NULL, *py_items = NULL;
     char *utf8 = NULL, *level1 = NULL, *level2 = NULL, *level3 = NULL;
     int32_t i = 0;
     Py_ssize_t cap = 0, l1s, l2s, l3s;
     UErrorCode status = U_ZERO_ERROR;
 
-    if (!PyArg_ParseTuple(args, "OOs#s#s#", &items, &sort_keys, &level1, &l1s, &level2, &l2s, &level3, &l3s)) return -1;
-    self->py_items = PySequence_Fast(items,  "Must pass in two sequence objects");
-    self->py_sort_keys = PySequence_Fast(sort_keys, "Must pass in two sequence objects");
-    if (self->py_items == NULL || self->py_sort_keys == NULL) goto end;
+    if (!PyArg_ParseTuple(args, "Os#s#s#", &items, &level1, &l1s, &level2, &l2s, &level3, &l3s)) return -1;
+    py_items = PySequence_Fast(items,  "Must pass in two sequence objects");
+    if (py_items == NULL) goto end;
     self->item_count = (uint32_t)PySequence_Size(items);
-    if (self->item_count != (uint32_t)PySequence_Size(sort_keys)) { PyErr_SetString(PyExc_TypeError, "The sequences must have the same length."); }
 
     self->items = (UChar**)calloc(self->item_count, sizeof(UChar*));
-    self->sort_items = (char**)calloc(self->item_count, sizeof(char*));
     self->item_lengths = (int32_t*)calloc(self->item_count, sizeof(uint32_t));
-    self->sort_item_lengths = (int32_t*)calloc(self->item_count, sizeof(uint32_t));
     self->level1 = (UChar*)calloc(alloc_uchar(l1s), sizeof(UChar));
     self->level2 = (UChar*)calloc(alloc_uchar(l2s), sizeof(UChar));
     self->level3 = (UChar*)calloc(alloc_uchar(l3s), sizeof(UChar));
 
-    if (self->items == NULL || self->sort_items == NULL || self->item_lengths == NULL || self->sort_item_lengths == NULL || self->level1 == NULL || self->level2 == NULL || self->level3 == NULL) {
+    if (self->items == NULL || self->item_lengths == NULL || self->level1 == NULL || self->level2 == NULL || self->level3 == NULL) {
         PyErr_NoMemory(); goto end; 
     }
+
     u_strFromUTF8Lenient(self->level1, alloc_uchar(l1s), &i, level1, (int32_t)l1s, &status);
     u_strFromUTF8Lenient(self->level2, alloc_uchar(l2s), &i, level2, (int32_t)l2s, &status);
     u_strFromUTF8Lenient(self->level3, alloc_uchar(l3s), &i, level3, (int32_t)l3s, &status);
     if (U_FAILURE(status)) { PyErr_SetString(PyExc_ValueError, "Failed to convert bytes for level string from UTF-8 to UTF-16"); goto end; }
 
     for (i = 0; i < self->item_count; i++) {
-        p = PySequence_Fast_GET_ITEM(self->py_items, i);
+        p = PySequence_Fast_GET_ITEM(py_items, i);
         utf8 = PyBytes_AsString(p);
         if (utf8 == NULL) goto end;
         cap = PyBytes_GET_SIZE(p); 
         self->items[i] = (UChar*)calloc(alloc_uchar(cap), sizeof(UChar));
         if (self->items[i] == NULL) { PyErr_NoMemory(); goto end; }
-        u_strFromUTF8Lenient(self->items[i], alloc_uchar(cap), &(self->item_lengths[i]), utf8, cap, &status);
+        u_strFromUTF8Lenient(self->items[i], alloc_uchar(cap), NULL, utf8, cap, &status);
         if (U_FAILURE(status)) { PyErr_SetString(PyExc_ValueError, "Failed to convert bytes from UTF-8 to UTF-16"); goto end; }
-
-        p = PySequence_Fast_GET_ITEM(self->py_sort_keys, i);
-        self->sort_items[i] = PyBytes_AsString(p);
-        if (self->sort_items[i] == NULL) goto end;
-        self->sort_item_lengths[i] = (uint32_t) PyBytes_GET_SIZE(p);
+        self->item_lengths[i] = u_strlen(self->items[i]);
     }
 
 end:
+    Py_XDECREF(py_items);
     if (PyErr_Occurred()) { free_matcher(self); }
     return (PyErr_Occurred()) ? -1 : 0;
 }
 // Matcher.__init__() }}}
  
-// Matcher.get_matches {{{
+// Matcher.calculate_scores {{{
 static PyObject *
-Matcher_get_matches(Matcher *self, PyObject *args) {
+Matcher_calculate_scores(Matcher *self, PyObject *args) {
     char *cneedle = NULL;
-    int32_t qsize = 0;
+    int32_t qsize = 0, *final_positions = NULL, *p;
     Match *matches = NULL;
     bool ok = FALSE;
-    uint32_t i = 0;
-    PyObject *items = NULL;
+    uint32_t i = 0, needle_char_len = 0, j = 0;
+    PyObject *items = NULL, *score = NULL, *positions = NULL;
     UErrorCode status = U_ZERO_ERROR;
     UChar *needle = NULL;
 
@@ -308,39 +387,48 @@ Matcher_get_matches(Matcher *self, PyObject *args) {
     if (needle == NULL) return PyErr_NoMemory();
     u_strFromUTF8Lenient(needle, alloc_uchar(qsize), &qsize, cneedle, qsize, &status);
     if (U_FAILURE(status)) { PyErr_SetString(PyExc_ValueError, "Failed to convert bytes from UTF-8 to UTF-16"); goto end; }
-
+    needle_char_len = u_countChar32(needle, -1);
     items = PyTuple_New(self->item_count);
+    positions = PyTuple_New(self->item_count);
     matches = (Match*)calloc(self->item_count, sizeof(Match));
-    if (items == NULL || matches == NULL) {PyErr_NoMemory(); goto end;}
+    final_positions = (int32_t*) calloc(needle_char_len * self->item_count, sizeof(int32_t));
+    if (items == NULL || matches == NULL || final_positions == NULL || positions == NULL) {PyErr_NoMemory(); goto end;}
+
     for (i = 0; i < self->item_count; i++) {
-        matches[i].item = self->items[i];
-        matches[i].sort_key = self->sort_items[i];
-        matches[i].sort_key_len = self->sort_item_lengths[i];
-        matches[i].py_item = PySequence_Fast_GET_ITEM(self->py_items, (Py_ssize_t)i);
+        score = PyTuple_New(needle_char_len);
+        if (score == NULL) { PyErr_NoMemory(); goto end; }
+        PyTuple_SET_ITEM(positions, (Py_ssize_t)i, score);
     }
 
     Py_BEGIN_ALLOW_THREADS;
-    ok = match(self->items, self->item_lengths, self->item_count, needle, (uint32_t)qsize, matches, self->level1, self->level2, self->level3);
-    if (ok) qsort(matches, self->item_count, sizeof(Match), cmp_score, NULL);
+    ok = match(self->items, self->item_lengths, self->item_count, needle, matches, final_positions, needle_char_len, self->level1, self->level2, self->level3);
     Py_END_ALLOW_THREADS;
 
     if (ok) {
         for (i = 0; i < self->item_count; i++) {
-            PyTuple_SET_ITEM(items, (Py_ssize_t)i, matches[i].py_item);
-            Py_INCREF(matches[i].py_item);
+            score = PyFloat_FromDouble(matches[i].score);
+            if (score == NULL) { PyErr_NoMemory(); goto end; }
+            PyTuple_SET_ITEM(items, (Py_ssize_t)i, score);
+            p = final_positions + i;
+            for (j = 0; j < needle_char_len; j++) {
+                score = PyInt_FromLong((long)p[j]);
+                if (score == NULL) { PyErr_NoMemory(); goto end; }
+                PyTuple_SET_ITEM(PyTuple_GET_ITEM(positions, (Py_ssize_t)i), (Py_ssize_t)j, score);
+            }
         }
     } else { PyErr_NoMemory(); goto end; }
 
 end:
     nullfree(needle);
     nullfree(matches);
-    if (PyErr_Occurred()) { Py_XDECREF(items); return NULL; }
-    return items;
+    nullfree(final_positions);
+    if (PyErr_Occurred()) { Py_XDECREF(items); items = NULL; Py_XDECREF(positions); positions = NULL; return NULL; }
+    return Py_BuildValue("NN", items, positions);
 } // }}}
 
 static PyMethodDef Matcher_methods[] = {
-    {"get_matches", (PyCFunction)Matcher_get_matches, METH_VARARGS,
-     "get_matches(query) -> Return the sorted list of matches for query which must be a UTF-8 encoded string."
+    {"calculate_scores", (PyCFunction)Matcher_calculate_scores, METH_VARARGS,
+     "calculate_scores(query) -> Return the scores for all items given query as a tuple."
     },
 
     {NULL}  /* Sentinel */

src/calibre/gui2/tweak_book/matcher.py

@@ -8,14 +8,19 @@ __copyright__ = '2014, Kovid Goyal <kovid at kovidgoyal.net>'
 
 from unicodedata import normalize
 
+from itertools import izip
 from future_builtins import map
 
 from calibre.constants import plugins
-from calibre.utils.icu import primary_sort_key
+from calibre.utils.icu import primary_sort_key, find
+
+DEFAULT_LEVEL1 = '/'
+DEFAULT_LEVEL2 = '-_ 0123456789'
+DEFAULT_LEVEL3 = '.'
 
 class Matcher(object):
 
-    def __init__(self, items, level1='/', level2='-_ 0123456789', level3='.'):
+    def __init__(self, items, level1=DEFAULT_LEVEL1, level2=DEFAULT_LEVEL2, level3=DEFAULT_LEVEL3):
         items = map(lambda x: normalize('NFC', unicode(x)), filter(None, items))
         items = tuple(map(lambda x: x.encode('utf-8'), items))
         sort_keys = tuple(map(primary_sort_key, items))
@@ -29,6 +34,96 @@ class Matcher(object):
         query = normalize('NFC', unicode(query)).encode('utf-8')
         return map(lambda x:x.decode('utf-8'), self.m.get_matches(query))
 
+
+def calc_score_for_char(ctx, prev, current, distance):
+    factor = 1.0
+    ans = ctx.max_score_per_char
+
+    if prev in ctx.level1:
+        factor = 0.9
+    elif prev in ctx.level2 or (icu_lower(prev) == prev and icu_upper(current) == current):
+        factor = 0.8
+    elif prev in ctx.level3:
+        factor = 0.7
+    else:
+        factor = (1.0 / distance) * 0.75
+
+    return ans * factor
+
+def process_item(ctx, haystack, needle):
+    # non-recursive implementation using a stack
+    stack = [(0, 0, 0, 0, [-1]*len(needle))]
+    final_score, final_positions = stack[0][-2:]
+    push, pop = stack.append, stack.pop
+    while stack:
+        hidx, nidx, last_idx, score, positions = pop()
+        key = (hidx, nidx, last_idx)
+        mem = ctx.memory.get(key, None)
+        if mem is None:
+            for i in xrange(nidx, len(needle)):
+                n = needle[i]
+                if (len(haystack) - hidx < len(needle) - i):
+                    score = 0
+                    break
+                pos = find(n, haystack[hidx:])[0] + hidx
+                if pos == -1:
+                    score = 0
+                    break
+
+                distance = pos - last_idx
+                score_for_char = ctx.max_score_per_char if distance <= 1 else calc_score_for_char(ctx, haystack[pos-1], haystack[pos], distance)
+                hidx = pos + 1
+                push((hidx, i, last_idx, score, list(positions)))
+                last_idx = positions[i] = pos
+                score += score_for_char
+            ctx.memory[key] = (score, positions)
+        else:
+            score, positions = mem
+        if score > final_score:
+            final_score = score
+            final_positions = positions
+    return final_score, final_positions
+
+class PyScorer(object):
+    __slots__ = ('level1', 'level2', 'level3', 'max_score_per_char', 'items', 'memory')
+
+    def __init__(self, items, level1=DEFAULT_LEVEL1, level2=DEFAULT_LEVEL2, level3=DEFAULT_LEVEL3):
+        self.level1, self.level2, self.level3 = level1, level2, level3
+        self.max_score_per_char = 0
+        self.items = map(lambda x: normalize('NFC', unicode(x)), filter(None, items))
+
+    def __call__(self, needle):
+        for item in self.items:
+            self.max_score_per_char = (1.0 / len(item) + 1.0 / len(needle)) / 2.0
+            self.memory = {}
+            yield process_item(self, item, needle)
+
+class CScorer(object):
+
+    def __init__(self, items, level1=DEFAULT_LEVEL1, level2=DEFAULT_LEVEL2, level3=DEFAULT_LEVEL3):
+        items = map(lambda x: normalize('NFC', unicode(x)), filter(None, items))
+        items = tuple(map(lambda x: x.encode('utf-8'), items))
+
+        speedup, err = plugins['matcher']
+        if speedup is None:
+            raise RuntimeError('Failed to load the matcher plugin with error: %s' % err)
+        self.m = speedup.Matcher(items, level1.encode('utf-8'), level2.encode('utf-8'), level3.encode('utf-8'))
+
+    def __call__(self, query):
+        query = normalize('NFC', unicode(query)).encode('utf-8')
+        scores, positions = self.m.calculate_scores(query)
+        for score, pos in izip(scores, positions):
+            yield score, pos
+
+def test():
+    items = ['m1mn34o/mno']
+    s = PyScorer(items)
+    c = CScorer(items)
+    for q in (s, c):
+        print (q)
+        for item, (score, positions) in izip(items, q('mno')):
+            print (item, score, positions)
+
 def test_mem():
     from calibre.utils.mem import gc_histogram, diff_hists
     m = Matcher([])
@@ -45,7 +140,8 @@ def test_mem():
     diff_hists(h1, h2)
 
 if __name__ == '__main__':
-    m = Matcher(['image/one.png', 'image/two.gif', 'text/one.html'])
-    for q in ('one', 'ton', 'imo'):
-        print (q, '->', tuple(m(q)))
-    test_mem()
+    test()
+    # m = Matcher(['image/one.png', 'image/two.gif', 'text/one.html'])
+    # for q in ('one', 'ONE', 'ton', 'imo'):
+    #     print (q, '->', tuple(m(q)))
+    # test_mem()