/*
* 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_POOL_SIZE (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_POOL_SIZE);
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_POOL_SIZE)
correct_pool_new();
data = (void*)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) {
const correct_trie_t *entries = t->entries;
unsigned char ch = *data;
const size_t vs = vec_size(entries);
size_t i;
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) {
correct_trie_t *entries = t->entries;
const size_t vs = vec_size(entries);
unsigned char ch = *data;
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 GMQCC_INLINE size_t *correct_find(correct_trie_t *table, const char *word) {
return (size_t*)correct_trie_get(table, word);
}
static GMQCC_INLINE bool correct_update(correct_trie_t* *table, const char *word) {
size_t *data = correct_find(*table, word);
if (!data)
return false;
(*data)++;
return true;
}
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;
/*
* As an experiment I tried the following assembly for memcmp here:
*
* correct_cmp_loop:
* incl %eax ; eax = LHS
* incl %edx ; edx = LRS
* cmpl %eax, %ebx ; ebx = &LHS[END_POS]
*
* jbe correct_cmp_eq
* movb (%edx), %cl ; micro-optimized on even atoms :-)
* cmpb %cl, (%eax) ; ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
* jg correct_cmp_gt
* jge correct_cmp_loop
* ...
*
* Despite how much optimization went in to this, the speed was the
* being conflicted by the strlen(ident) used for &LHS[END_POS]
* If we could eliminate the strlen with what I suggested on line
* 311 ... we can accelerate this whole damn thing quite a bit.
*
* However there is still something we can do here that does give
* us a little more speed. Although one more branch, we know for
* sure there is at least one byte to compare, if that one byte
* simply isn't the same we can skip the full check. Which means
* we skip a whole strlen call.
*/
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);
}