Claudenw commented on code in PR #501:
URL:
https://github.com/apache/commons-collections/pull/501#discussion_r1635902965
##########
src/main/java/org/apache/commons/collections4/bloomfilter/EnhancedDoubleHasher.java:
##########
@@ -167,41 +167,33 @@ public boolean processIndices(final IntPredicate
consumer) {
// hash[i] = ( h1(x) - i*h2(x) - (i*i*i - i)/6 ) wrapped in
[0, bits)
int index = BitMaps.mod(initial, bits);
+ if (!consumer.test(index)) {
+ return false;
+ }
int inc = BitMaps.mod(increment, bits);
final int k = shape.getNumberOfHashFunctions();
- if (k > bits) {
- for (int j = k; j > 0;) {
- // handle k > bits
- final int block = Math.min(j, bits);
- j -= block;
- for (int i = 1; i <= block; i++) {
- if (!consumer.test(index)) {
- return false;
- }
- // Update index and handle wrapping
- index -= inc;
- index = index < 0 ? index + bits : index;
-
- // Incorporate the counter into the increment to
create a
- // tetrahedral number additional term, and handle
wrapping.
- inc -= i;
- inc = inc < 0 ? inc + bits : inc;
- }
+
+ // the tetraheadral incrementer. We need to ensure that this
+ // number does not exceed bits-1 or we may end up with an
index > bits.
+ int tet = 1;
+ for (int i = 1; i < k; i++) {
+ // Update index and handle wrapping
+ index -= inc;
+ index = index < 0 ? index + bits : index;
+ if (!consumer.test(index)) {
+ return false;
+ }
+
+ // Incorporate the counter into the increment to create a
+ // tetrahedral number additional term, and handle wrapping.
+ inc -= tet;
+ inc = inc < 0 ? inc + bits : inc;
+ if (inc >= bits) {
+ inc = BitMaps.mod(increment, bits);
Review Comment:
```
// the tetraheadral incrementer. We need to ensure that this
// number does not exceed bits-1 or we may end up with an
index > bits.
int tet = 1;
for (int i = 1; i < k; i++) {
// Update index and handle wrapping
index -= inc;
index = index < 0 ? index + bits : index;
if (!consumer.test(index)) {
return false;
}
// Incorporate the counter into the increment to create a
// tetrahedral number additional term, and handle
wrapping.
inc -= tet;
inc = inc < 0 ? inc + bits : inc;
if (++tet == bits) {
tet = 0;
}
}
```
The difference between this block and a single simple path is the increment
of tet and the if check near the bottom of the block. I don't think this is a
significant overhead and significantly simplifies the code. We should also
consider that generating the values from the hash is considered an expensive
operation so the slight overhead here is not unexpected and I believe faster
than executing multiple murmur3 hashes for example.
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