Actually, the jaccard distance is defined as D = 1 - intersect / union.
Additionally, the distance value is compared against a constant that
must be between 0 and 1, which is not the case here. Both facts together
has led to the fact, that the function always returned a matching course
signature. To leave the constant intact and to avoid floating point
computation, this commit multiplies with 1 << 16 making the constant
effectively 9000 / (1<<16) =~ 0.14.
Reported-by: Sachin Tilloo <sachin.til...@gmail.com>
Reviewed-by: Sachin Tilloo <sachin.til...@gmail.com>
Tested-by: Sachin Tilloo <sachin.til...@gmail.com>
---
Sorry, it should apply clean now.
libavfilter/signature_lookup.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/libavfilter/signature_lookup.c b/libavfilter/signature_lookup.c
index a0ca818a9b..46602874de 100644
--- a/libavfilter/signature_lookup.c
+++ b/libavfilter/signature_lookup.c
@@ -127,9 +127,10 @@ static int get_jaccarddist(SignatureContext *sc,
CoarseSignature *first, CoarseS
{
int jaccarddist, i, composdist = 0, cwthcount = 0;
for (i = 0; i < 5; i++) {
- if ((jaccarddist = intersection_word(first->data[i], second->data[i]))
> 0) {
+ if ((jaccarddist = (1 << 16) * intersection_word(first->data[i],
second->data[i])) > 0) {
jaccarddist /= union_word(first->data[i], second->data[i]);
}
+ jaccarddist = (1 << 16) - jaccarddist;
if (jaccarddist >= sc->thworddist) {
if (++cwthcount > 2) {
/* more than half (5/2) of distances are too wide */
--
2.43.2
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