msokolov commented on a change in pull request #2047:
URL: https://github.com/apache/lucene-solr/pull/2047#discussion_r518030964
##########
File path: lucene/core/src/java/org/apache/lucene/util/VectorUtil.java
##########
@@ -25,47 +25,22 @@
private VectorUtil() {
}
- public static float dotProduct(float[] a, float[] b) {
- float res = 0f;
- /*
- * If length of vector is larger than 8, we use unrolled dot product to
accelerate the
- * calculation.
- */
- int i;
- for (i = 0; i < a.length % 8; i++) {
- res += b[i] * a[i];
- }
- if (a.length < 8) {
- return res;
- }
- float s0 = 0f;
- float s1 = 0f;
- float s2 = 0f;
- float s3 = 0f;
- float s4 = 0f;
- float s5 = 0f;
- float s6 = 0f;
- float s7 = 0f;
- for (; i + 7 < a.length; i += 8) {
- s0 += b[i] * a[i];
- s1 += b[i + 1] * a[i + 1];
- s2 += b[i + 2] * a[i + 2];
- s3 += b[i + 3] * a[i + 3];
- s4 += b[i + 4] * a[i + 4];
- s5 += b[i + 5] * a[i + 5];
- s6 += b[i + 6] * a[i + 6];
- s7 += b[i + 7] * a[i + 7];
+ public static double dotProduct(float[] a, float[] b) {
Review comment:
That's a fair comment. I put this in because we had someone do some
extensive work on trying to optimize this code loop, and he found that
unrolling like this made it more amenable to being expressed as AVX
instructions, leading to some speedup, but it wasn't huge. Still - would you
mind running some microbenchmark to see if there is any measurable change in
performance with this?
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