122 lines
2.6 KiB
C++
122 lines
2.6 KiB
C++
// @BAKE clang -shared -fPIC -Isqlite3 -o damerau_levenshtein.sqlext damerau_levenshtein.c
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#include <sqlite3.h>
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#include <stdlib.h>
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#include <string.h>
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#include <limits.h>
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// helpers
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int minimum(const int a, const int b, const int c);
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/* internal function for damerau-levenshtein distance calculation
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*/
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static int
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damerau_levenshtein_(
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int n,
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const char *const s,
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int m,
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const char *const t
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){
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//Step 1
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if ((n == 0) || (m == 0)) {
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return 0;
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}
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int *d = (int*)malloc(sizeof(int)*(m+1)*(n+1));
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m++;
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n++;
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//Step 2
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int k;
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for(k=0;k<n;k++) d[k]=k;
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for(k=0;k<m;k++) d[k*n]=k;
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//Step 3 and 4
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int i, j;
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for(i=1; i<n; i++) {
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for(j=1; j<m; j++) {
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int cost;
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//Step 5
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//cost = s[i-1] != t[j-1];
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if (s[i-1] == t[j-1]) {
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cost = 0;
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}
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else {
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cost = 1;
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}
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//Step 6
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d[j*n+i] = minimum(d[(j-1)*n+i]+1, d[j*n+i-1]+1, d[(j-1)*n+i-1]+cost);
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//Step 7 – only difference from pure Levenshtein - transposition
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if ( (i > 1) && (j > 1) && (s[i-1] == t[j-2]) && (s[i-2] == t[j-1]) ) {
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d[j*n+i] = minimum(INT_MAX,
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d[j*n+i],
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d[(j-2)*n+(i-2)] + cost);
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}
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}
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}
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const int distance = d[n*m-1];
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free(d);
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return distance;
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}
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/*
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function to determine damerau-levenshtein distance
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damerau_levenshtein(src,dts) => int
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*/
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void
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damerau_levenshtein(
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sqlite3_context *context,
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int argc,
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sqlite3_value **argv
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){
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const char *const s = (const char *)sqlite3_value_text(argv[0]);
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const char *const t = (const char *)sqlite3_value_text(argv[1]);
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const int n = strlen(s);
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const int m = strlen(t);
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const int distance = damerau_levenshtein_(n, s, m, t);
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sqlite3_result_int(context, distance);
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}
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/*
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function ensure damerau-levenshtein distance
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damerau_levenshtein(src,dts,max_distance) => bool
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*/
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void
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is_damerau_levenshtein(
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sqlite3_context *context,
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int argc,
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sqlite3_value **argv
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){
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const char *const s = (const char *)sqlite3_value_text(argv[0]);
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const char *const t = (const char *)sqlite3_value_text(argv[1]);
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const int n = strlen(s);
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const int m = strlen(t);
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const int max_distance = sqlite3_value_int(argv[2]);
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if (abs(n - m) > max_distance) {
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sqlite3_result_int(context, 0);
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return;
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}
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const int distance = damerau_levenshtein_(n, s, m, t);
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sqlite3_result_int(context, distance <= max_distance);
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}
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inline int minimum(const int a, const int b, const int c) {
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int min = a;
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if (b < min) min=b;
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if (c < min) min=c;
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return min;
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}
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