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#include "distance.h"
static short
fastcomp(unicode *seq1, unicode *seq2, Py_ssize_t len1, Py_ssize_t len2, int transpositions)
{
char *models[3];
short m, cnt, res = 3;
Py_ssize_t i, j, c, ldiff;
#ifdef SEQUENCE_COMP
int comp;
#endif
if (len1 < len2) {
SWAP(unicode *, seq1, seq2);
SWAP(Py_ssize_t, len1, len2);
}
ldiff = len1 - len2;
switch (ldiff) {
case 0:
models[2] = "id";
models[1] = "di";
models[0] = "rr";
m = 2;
break;
case 1:
models[1] = "dr";
models[0] = "rd";
m = 1;
break;
case 2:
models[0] = "dd";
m = 0;
break;
default:
return -1;
}
for (; m >= 0; m--) {
i = j = c = 0;
while (i < len1 && j < len2)
{
#ifdef SEQUENCE_COMP
comp = SEQUENCE_COMP(seq1, i, seq2, j);
if (comp == -1)
return -2;
if (!comp) {
#else
if (seq1[i] != seq2[j]) {
#endif
c++;
if (c > 2)
break;
/* Transpositions handling. `ldiff`, which is the absolute difference between the length
of the sequences `seq1` and `seq2`, should not be equal to 2 because in this case only
deletions can happen (given that the distance between the two sequences should not be
higher than 2, this is the shortest path).
We do a lookahead to check if a transposition is possible between the current position
and the next one, and, if so, we systematically choose this path over the other alternative
edit operations. We act like so because the cost of a transposition is always the lowest
one in such situations.
*/
#ifdef SEQUENCE_COMP
if (transpositions && ldiff != 2 && i < (len1 - 1) && j < (len2 - 1)) {
comp = SEQUENCE_COMP(seq1, i + 1, seq2, j);
if (comp == -1)
return -2;
else if (comp) {
comp = SEQUENCE_COMP(seq1, i, seq2, j + 1);
if (comp == -1)
return -2;
else if (comp) {
i = i + 2;
j = j + 2;
continue;
}
}
}
#else
if (transpositions && ldiff != 2 && i < (len1 - 1) && j < (len2 - 1) && \
seq1[i + 1] == seq2[j] && \
seq1[i] == seq2[j + 1]) {
i = i + 2;
j = j + 2;
continue;
}
#endif
if (models[m][c - 1] == 'd')
i++;
else if (models[m][c - 1] == 'i')
j++;
else {
i++;
j++;
}
}
else {
i++;
j++;
}
}
if (c > 2)
continue;
else if (i < len1) {
if (c == 1)
cnt = (models[m][1] == 'd');
else
cnt = (models[m][0] == 'd') + (models[m][1] == 'd');
if (len1 - i <= cnt) {
c = c + (len1 - i);
}
else
continue;
}
else if (j < len2) {
if (len2 - j <= (models[m][c] == 'i'))
c = c + (len2 - j);
else
continue;
}
if (c < res) {
res = c;
}
}
if (res == 3)
res = -1;
return res;
}
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