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Cleanups and documentation

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Dale Weiler 2013-01-06 03:06:56 +00:00
parent 294870c5ba
commit 7e87c61d78
1 changed files with 99 additions and 75 deletions
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174
correct.c
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@ -22,6 +22,77 @@
*/ */
#include "gmqcc.h" #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.
*
* Bayes' Therom suggests something of the following:
* AC P(I|C) P(C) / P(I)
* Since P(I) is the same for every possibly I, we can ignore it giving
* 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.
*
* 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%
*/
#define CORRECT_POOLSIZE (128*1024*1024)
/* /*
* A forward allcator for the corrector. This corrector requires a lot * A forward allcator for the corrector. This corrector requires a lot
* of allocations. This forward allocator combats all those allocations * of allocations. This forward allocator combats all those allocations
@ -29,8 +100,6 @@
* allocation isn't wasting a little header space for when NOTRACK isn't * allocation isn't wasting a little header space for when NOTRACK isn't
* defined. * defined.
*/ */
#define CORRECT_POOLSIZE (128*1024*1024)
static unsigned char **correct_pool_data = NULL; static unsigned char **correct_pool_data = NULL;
static unsigned char *correct_pool_this = NULL; static unsigned char *correct_pool_this = NULL;
static size_t correct_pool_addr = 0; static size_t correct_pool_addr = 0;
@ -65,30 +134,35 @@ static GMQCC_INLINE void correct_pool_delete(void) {
} }
static GMQCC_INLINE char *correct_outstr(const char *s) { static GMQCC_INLINE char *correct_pool_claim(const char *data) {
char *o = util_strdup(s); char *claim = util_strdup(data);
correct_pool_delete(); correct_pool_delete();
return o; return claim;
} }
correct_trie_t* correct_trie_new() /*
{ * A fast space efficent trie for a disctonary 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. Very Very Slow.
*/
correct_trie_t* correct_trie_new() {
correct_trie_t *t = (correct_trie_t*)mem_a(sizeof(correct_trie_t)); correct_trie_t *t = (correct_trie_t*)mem_a(sizeof(correct_trie_t));
t->value = NULL; t->value = NULL;
t->entries = NULL; t->entries = NULL;
return t; return t;
} }
void correct_trie_del_sub(correct_trie_t *t) void correct_trie_del_sub(correct_trie_t *t) {
{
size_t i; size_t i;
for (i = 0; i < vec_size(t->entries); ++i) for (i = 0; i < vec_size(t->entries); ++i)
correct_trie_del_sub(&t->entries[i]); correct_trie_del_sub(&t->entries[i]);
vec_free(t->entries); vec_free(t->entries);
} }
void correct_trie_del(correct_trie_t *t) void correct_trie_del(correct_trie_t *t) {
{
size_t i; size_t i;
for (i = 0; i < vec_size(t->entries); ++i) for (i = 0; i < vec_size(t->entries); ++i)
correct_trie_del_sub(&t->entries[i]); correct_trie_del_sub(&t->entries[i]);
@ -96,8 +170,7 @@ void correct_trie_del(correct_trie_t *t)
mem_d(t); mem_d(t);
} }
void* correct_trie_get(const correct_trie_t *t, const char *key) void* correct_trie_get(const correct_trie_t *t, const char *key) {
{
const unsigned char *data = (const unsigned char*)key; const unsigned char *data = (const unsigned char*)key;
while (*data) { while (*data) {
unsigned char ch = *data; unsigned char ch = *data;
@ -117,8 +190,7 @@ void* correct_trie_get(const correct_trie_t *t, const char *key)
return t->value; return t->value;
} }
void correct_trie_set(correct_trie_t *t, const char *key, void * const value) void correct_trie_set(correct_trie_t *t, const char *key, void * const value) {
{
const unsigned char *data = (const unsigned char*)key; const unsigned char *data = (const unsigned char*)key;
while (*data) { while (*data) {
unsigned char ch = *data; unsigned char ch = *data;
@ -143,57 +215,11 @@ void correct_trie_set(correct_trie_t *t, const char *key, void * const value)
t->value = value; t->value = value;
} }
/*
* 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 implies that 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.
*
* Bayes' Therom suggests something of the following:
* AC P(I|C) P(C) / P(I)
* Since P(I) is the same for every possibly I, we can ignore it giving
* 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, which implies the enumeration of all
* feasible values of C, and then determine the one that gives the
* greatest probability score. Selecting it as the "correction"
*
*
* The requirement for complex expression involving two models:
*
* 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.
*/
/* some hashtable management for dictonaries */ /*
* 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) { static size_t *correct_find(correct_trie_t *table, const char *word) {
return (size_t*)correct_trie_get(table, word); return (size_t*)correct_trie_get(table, word);
} }
@ -420,7 +446,6 @@ char *correct_str(correct_trie_t* table, const char *ident) {
char **e2; char **e2;
char *e1ident; char *e1ident;
char *e2ident; char *e2ident;
char *found = util_strdup(ident);
size_t e1rows = 0; size_t e1rows = 0;
size_t e2rows = 0; size_t e2rows = 0;
@ -429,21 +454,20 @@ char *correct_str(correct_trie_t* table, const char *ident) {
/* needs to be allocated for free later */ /* needs to be allocated for free later */
if (correct_find(table, ident)) if (correct_find(table, ident))
return correct_outstr(found); return correct_pool_claim(ident);
if ((e1rows = correct_size(ident))) { if ((e1rows = correct_size(ident))) {
e1 = correct_edit(ident); e1 = correct_edit(ident);
if ((e1ident = correct_maximum(table, e1, e1rows))) { if ((e1ident = correct_maximum(table, e1, e1rows)))
found = util_strdup(e1ident); return correct_pool_claim(e1ident);
return correct_outstr(found);
}
} }
e2 = correct_known(table, e1, e1rows, &e2rows); e2 = correct_known(table, e1, e1rows, &e2rows);
if (e2rows && ((e2ident = correct_maximum(table, e2, e2rows)))) { if (e2rows && ((e2ident = correct_maximum(table, e2, e2rows))))
found = util_strdup(e2ident); return correct_pool_claim(e2ident);
}
return correct_outstr(found);
correct_pool_delete();
return util_strdup(ident);
} }