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/*
* Copyright (c) 2018 Pablo Neira Ayuso <pablo@netfilter.org>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 (or any
* later) as published by the Free Software Foundation.
*/
#include <nft.h>
#include <limits.h>
#include <utils.h>
#include <misspell.h>
enum string_distance_function {
DELETION = 0, /* m1 */
INSERTION, /* m2 */
TRANSFORMATION, /* m3 */
};
#define DISTANCE_MAX (TRANSFORMATION + 1)
static unsigned int min_distance(unsigned int *cost)
{
unsigned int min = UINT_MAX;
int k;
for (k = 0; k < DISTANCE_MAX; k++) {
if (cost[k] < min)
min = cost[k];
}
return min;
}
/* A simple implementation of "The string-to-string correction problem (1974)"
* by Robert A. Wagner.
*/
static unsigned int string_distance(const char *a, const char *b)
{
unsigned int len_a = strlen(a);
unsigned int len_b = strlen(b);
unsigned int *distance;
unsigned int i, j, ret;
distance = xzalloc((len_a + 1) * (len_b + 1) * sizeof(unsigned int));
#define DISTANCE(__i, __j) distance[(__i) * len_b + (__j)]
for (i = 0; i <= len_a; i++)
DISTANCE(i, 0) = i;
for (j = 0; j <= len_b; j++)
DISTANCE(0, j) = j;
for (i = 1; i <= len_a; i++) {
for (j = 1; j <= len_b; j++) {
unsigned int subcost = (a[i] == b[j]) ? 0 : 1;
unsigned int cost[3];
cost[DELETION] = DISTANCE(i - 1, j) + 1;
cost[INSERTION] = DISTANCE(i, j - 1) + 1;
cost[TRANSFORMATION] = DISTANCE(i - 1, j - 1) + subcost;
DISTANCE(i, j) = min_distance(cost);
if (i > 1 && j > 1 &&
a[i] == b[j - 1] &&
a[i - 1] == b[j])
DISTANCE(i, j) =
min(DISTANCE(i, j),
DISTANCE(i - 2, j - 2) + subcost);
}
}
ret = DISTANCE(len_a, len_b);
xfree(distance);
return ret;
}
void string_misspell_init(struct string_misspell_state *st)
{
st->obj = NULL;
st->min_distance = UINT_MAX;
}
int string_misspell_update(const char *a, const char *b,
void *obj, struct string_misspell_state *st)
{
unsigned int len_a, len_b, max_len, min_len, distance, threshold;
len_a = strlen(a);
len_b = strlen(b);
max_len = max(len_a, len_b);
min_len = min(len_a, len_b);
if (max_len <= 1)
return 0;
if (max_len - min_len <= 1)
threshold = max(div_round_up(max_len, 3), 1);
else
threshold = div_round_up(max_len + 2, 3);
distance = string_distance(a, b);
if (distance > threshold)
return 0;
else if (distance < st->min_distance) {
st->min_distance = distance;
st->obj = obj;
return 1;
}
return 0;
}
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