/* * Copyright (C) 2012, 2013 * Dale Weiler * Wolfgang Bumiller * * Permission is hereby granted, free of charge, to any person obtaining a copy of * this software and associated documentation files (the "Software"), to deal in * the Software without restriction, including without limitation the rights to * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies * of the Software, and to permit persons to whom the Software is furnished to do * so, subject to the following conditions: * * The above copyright notice and this permission notice shall be included in all * copies or substantial portions of the Software. * * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE * SOFTWARE. */ #include "gmqcc.h" /* * This is a very clever method for correcting mistakes in QuakeC code * most notably when invalid identifiers are used or inproper assignments; * we can proprly lookup in multiple dictonaries (depening on the rules * of what the task is trying to acomplish) to find the best possible * match. * * * A little about how it works, and probability theory: * * When given an identifier (which we will denote I), we're essentially * just trying to choose the most likely correction for that identifier. * (the actual "correction" can very well be the identifier itself). * There is actually no way to know for sure that certian identifers * such as "lates", need to be corrected to "late" or "latest" or any * other permutations that look lexically the same. This is why we * must advocate the usage of probabilities. This means that instead of * just guessing, instead we're trying to find the correction for C, * out of all possible corrections that maximizes the probability of C * for the original identifer I. * * Thankfully there exists some theroies for probalistic interpretations * of data. Since we're operating on two distictive intepretations, the * transposition from I to C. We need something that can express how much * degree of I should rationally change to become C. this is called the * Bayesian interpretation. You can read more about it from here: * http://www.celiagreen.com/charlesmccreery/statistics/bayestutorial.pdf * (which is probably the only good online documentation for bayes theroy * no lie. Everything else just sucks ..) * * Bayes' Thereom suggests something like the following: * AC P(I|C) P(C) / P(I) * * However since P(I) is the same for every possibility of I, we can * completley ignore it giving just: * AC P(I|C) P(C) * * This greatly helps visualize how the parts of the expression are performed * there is essentially three, from right to left we perform the following: * * 1: P(C), the probability that a proposed correction C will stand on its * own. This is called the language model. * * 2: P(I|C), the probability that I would be used, when the programmer * really meant C. This is the error model. * * 3: AC, the control mechanisim, an enumerator if you will, one that * enumerates all feasible values of C, to determine the one that * gives the greatest probability score. * * In reality the requirement for a more complex expression involving * two seperate models is considerably a waste. But one must recognize * that P(C|I) is already conflating two factors. It's just much simpler * to seperate the two models and deal with them explicitaly. To properly * estimate P(C|I) you have to consider both the probability of C and * probability of the transposition from C to I. It's simply much more * cleaner, and direct to seperate the two factors. * * Research tells us that 80% to 95% of all spelling errors have an edit * distance no greater than one. Knowing this we can optimize for most * cases of mistakes without taking a performance hit. Which is what we * base longer edit distances off of. Opposed to the original method of * I had concieved of checking everything. * * A little information on additional algorithms used: * * Initially when I implemented this corrector, it was very slow. * Need I remind you this is essentially a brute force attack on strings, * and since every transformation requires dynamic memory allocations, * you can easily imagine where most of the runtime conflated. Yes * It went right to malloc. More than THREE MILLION malloc calls are * performed for an identifier about 16 bytes long. This was such a * shock to me. A forward allocator (or as some call it a bump-point * allocator, or just a memory pool) was implemented. To combat this. * * But of course even other factors were making it slow. Initially * this used a hashtable. And hashtables have a good constant lookup * time complexity. But the problem wasn't in the hashtable, it was * in the hashing (despite having one of the fastest hash functions * known). Remember those 3 million mallocs? Well for every malloc * there is also a hash. After 3 million hashes .. you start to get * very slow. To combat this I had suggested burst tries to Blub. * The next day he had implemented them. Sure enough this brought * down the runtime by a factory > 100% * * Future Work (If we really need it) * * Currently we can only distinguishes one source of error in the * language model we use. This could become an issue for identifiers * that have close colliding rates, e.g colate->coat yields collate. * * Currently the error model has been fairly trivial, the smaller the * edit distance the smaller the error. This usually causes some un- * expected problems. e.g reciet->recite yields recipt. For QuakeC * this could become a problem when lots of identifiers are involved. * * Our control mechanisim could use a limit, i.e limit the number of * sets of edits for distance X. This would also increase execution * speed considerably. */ #define CORRECT_POOLSIZE (128*1024*1024) /* * A forward allcator for the corrector. This corrector requires a lot * of allocations. This forward allocator combats all those allocations * and speeds us up a little. It also saves us space in a way since each * allocation isn't wasting a little header space for when NOTRACK isn't * defined. */ static unsigned char **correct_pool_data = NULL; static unsigned char *correct_pool_this = NULL; static size_t correct_pool_addr = 0; static GMQCC_INLINE void correct_pool_new(void) { correct_pool_addr = 0; correct_pool_this = (unsigned char *)mem_a(CORRECT_POOLSIZE); vec_push(correct_pool_data, correct_pool_this); } static GMQCC_INLINE void *correct_pool_alloc(size_t bytes) { void *data; if (correct_pool_addr + bytes >= CORRECT_POOLSIZE) correct_pool_new(); data = correct_pool_this; correct_pool_this += bytes; correct_pool_addr += bytes; return data; } static GMQCC_INLINE void correct_pool_delete(void) { size_t i; for (i = 0; i < vec_size(correct_pool_data); ++i) mem_d(correct_pool_data[i]); correct_pool_data = NULL; correct_pool_this = NULL; correct_pool_addr = 0; } static GMQCC_INLINE char *correct_pool_claim(const char *data) { char *claim = util_strdup(data); correct_pool_delete(); return claim; } /* * A fast space efficent trie for a dictionary of identifiers. This is * faster than a hashtable for one reason. A hashtable itself may have * fast constant lookup time, but the hash itself must be very fast. We * have one of the fastest hash functions for strings, but if you do a * lost of hashing (which we do, almost 3 million hashes per identifier) * a hashtable becomes slow. */ correct_trie_t* correct_trie_new() { correct_trie_t *t = (correct_trie_t*)mem_a(sizeof(correct_trie_t)); t->value = NULL; t->entries = NULL; return t; } void correct_trie_del_sub(correct_trie_t *t) { size_t i; for (i = 0; i < vec_size(t->entries); ++i) correct_trie_del_sub(&t->entries[i]); vec_free(t->entries); } void correct_trie_del(correct_trie_t *t) { size_t i; for (i = 0; i < vec_size(t->entries); ++i) correct_trie_del_sub(&t->entries[i]); vec_free(t->entries); mem_d(t); } void* correct_trie_get(const correct_trie_t *t, const char *key) { const unsigned char *data = (const unsigned char*)key; while (*data) { unsigned char ch = *data; const size_t vs = vec_size(t->entries); size_t i; const correct_trie_t *entries = t->entries; for (i = 0; i < vs; ++i) { if (entries[i].ch == ch) { t = &entries[i]; ++data; break; } } if (i == vs) return NULL; } return t->value; } void correct_trie_set(correct_trie_t *t, const char *key, void * const value) { const unsigned char *data = (const unsigned char*)key; while (*data) { const size_t vs = vec_size(t->entries); unsigned char ch = *data; correct_trie_t *entries = t->entries; size_t i; for (i = 0; i < vs; ++i) { if (entries[i].ch == ch) { t = &entries[i]; break; } } if (i == vs) { correct_trie_t *elem = (correct_trie_t*)vec_add(t->entries, 1); elem->ch = ch; elem->value = NULL; elem->entries = NULL; t = elem; } ++data; } t->value = value; } /* * Implementation of the corrector algorithm commences. A very efficent * brute-force attack (thanks to tries and mempool :-)). */ static size_t *correct_find(correct_trie_t *table, const char *word) { return (size_t*)correct_trie_get(table, word); } static int correct_update(correct_trie_t* *table, const char *word) { size_t *data = correct_find(*table, word); if (!data) return 0; (*data)++; return 1; } void correct_add(correct_trie_t* table, size_t ***size, const char *ident) { size_t *data = NULL; const char *add = ident; if (!correct_update(&table, add)) { data = (size_t*)mem_a(sizeof(size_t)); *data = 1; vec_push((*size), data); correct_trie_set(table, add, data); } } void correct_del(correct_trie_t* dictonary, size_t **data) { size_t i; const size_t vs = vec_size(data); for (i = 0; i < vs; i++) mem_d(data[i]); vec_free(data); correct_trie_del(dictonary); } /* * _ is valid in identifiers. I've yet to implement numerics however * because they're only valid after the first character is of a _, or * alpha character. */ static const char correct_alpha[] = "abcdefghijklmnopqrstuvwxyz" "ABCDEFGHIJKLMNOPQRSTUVWXYZ" "_"; /* TODO: Numbers ... */ /* * correcting logic for the following forms of transformations: * 1) deletion * 2) transposition * 3) alteration * 4) insertion * * These functions could take an additional size_t **size paramater * and store back the results of their new length in an array that * is the same as **array for the memcmp in correct_exists. I'm just * not able to figure out how to do that just yet. As my brain is * not in the mood to figure out that logic. This is a reminder to * do it, or for someone else to :-) correct_edit however would also * need to take a size_t ** to carry it along (would all the argument * overhead be worth it?) */ static size_t correct_deletion(const char *ident, char **array, size_t index) { size_t itr = 0; const size_t len = strlen(ident); for (; itr < len; itr++) { char *a = (char*)correct_pool_alloc(len+1); memcpy(a, ident, itr); memcpy(a + itr, ident + itr + 1, len - itr); array[index + itr] = a; } return itr; } static size_t correct_transposition(const char *ident, char **array, size_t index) { size_t itr = 0; const size_t len = strlen(ident); for (; itr < len - 1; itr++) { char tmp; char *a = (char*)correct_pool_alloc(len+1); memcpy(a, ident, len+1); tmp = a[itr]; a[itr ] = a[itr+1]; a[itr+1] = tmp; array[index + itr] = a; } return itr; } static size_t correct_alteration(const char *ident, char **array, size_t index) { size_t itr = 0; size_t jtr = 0; size_t ktr = 0; const size_t len = strlen(ident); for (; itr < len; itr++) { for (jtr = 0; jtr < sizeof(correct_alpha)-1; jtr++, ktr++) { char *a = (char*)correct_pool_alloc(len+1); memcpy(a, ident, len+1); a[itr] = correct_alpha[jtr]; array[index + ktr] = a; } } return ktr; } static size_t correct_insertion(const char *ident, char **array, size_t index) { size_t itr = 0; size_t jtr = 0; size_t ktr = 0; const size_t len = strlen(ident); for (; itr <= len; itr++) { for (jtr = 0; jtr < sizeof(correct_alpha)-1; jtr++, ktr++) { char *a = (char*)correct_pool_alloc(len+2); memcpy(a, ident, itr); memcpy(a + itr + 1, ident + itr, len - itr + 1); a[itr] = correct_alpha[jtr]; array[index + ktr] = a; } } return ktr; } static GMQCC_INLINE size_t correct_size(const char *ident) { /* * deletion = len * transposition = len - 1 * alteration = len * sizeof(correct_alpha) * insertion = (len + 1) * sizeof(correct_alpha) */ register size_t len = strlen(ident); return (len) + (len - 1) + (len * (sizeof(correct_alpha)-1)) + ((len + 1) * (sizeof(correct_alpha)-1)); } static char **correct_edit(const char *ident) { size_t next; char **find = (char**)correct_pool_alloc(correct_size(ident) * sizeof(char*)); if (!find) return NULL; next = correct_deletion (ident, find, 0); next += correct_transposition(ident, find, next); next += correct_alteration (ident, find, next); /*****/ correct_insertion (ident, find, next); return find; } /* * We could use a hashtable but the space complexity isn't worth it * since we're only going to determine the "did you mean?" identifier * on error. */ static int correct_exist(char **array, size_t rows, char *ident) { size_t itr; for (itr = 0; itr < rows; itr++) if (!memcmp(array[itr], ident, strlen(ident))) return 1; return 0; } static GMQCC_INLINE char **correct_known_resize(char **res, size_t *allocated, size_t size) { size_t oldallocated = *allocated; char **out; if (size+1 < *allocated) return res; *allocated += 32; out = correct_pool_alloc(sizeof(*res) * *allocated); memcpy(out, res, sizeof(*res) * oldallocated); return out; } static char **correct_known(correct_trie_t* table, char **array, size_t rows, size_t *next) { size_t itr = 0; size_t jtr = 0; size_t len = 0; size_t row = 0; size_t nxt = 8; char **res = correct_pool_alloc(sizeof(char *) * nxt); char **end = NULL; for (; itr < rows; itr++) { end = correct_edit(array[itr]); row = correct_size(array[itr]); /* removing jtr=0 here speeds it up by 100ms O_o */ for (jtr = 0; jtr < row; jtr++) { if (correct_find(table, end[jtr]) && !correct_exist(res, len, end[jtr])) { res = correct_known_resize(res, &nxt, len+1); res[len++] = end[jtr]; } } } *next = len; return res; } static char *correct_maximum(correct_trie_t* table, char **array, size_t rows) { char *str = NULL; size_t *itm = NULL; size_t itr = 0; size_t top = 0; for (; itr < rows; itr++) { if ((itm = correct_find(table, array[itr])) && (*itm > top)) { top = *itm; str = array[itr]; } } return str; } /* * This is the exposed interface: * takes a table for the dictonary a vector of sizes (used for internal * probability calculation, and an identifier to "correct" * * the add function works the same. Except the identifier is used to * add to the dictonary. */ char *correct_str(correct_trie_t* table, const char *ident) { char **e1 = NULL; char **e2 = NULL; char *e1ident = NULL; char *e2ident = NULL; size_t e1rows = 0; size_t e2rows = 0; correct_pool_new(); /* needs to be allocated for free later */ if (correct_find(table, ident)) return correct_pool_claim(ident); if ((e1rows = correct_size(ident))) { e1 = correct_edit(ident); if ((e1ident = correct_maximum(table, e1, e1rows))) return correct_pool_claim(e1ident); } e2 = correct_known(table, e1, e1rows, &e2rows); if (e2rows && ((e2ident = correct_maximum(table, e2, e2rows)))) return correct_pool_claim(e2ident); correct_pool_delete(); return util_strdup(ident); }