yx-keith commented on code in PR #62840:
URL: https://github.com/apache/doris/pull/62840#discussion_r3309635908
##########
be/src/exprs/function/array/function_array_distance.cpp:
##########
@@ -31,15 +39,32 @@ float CosineDistance::distance(const float* x, const float*
y, size_t d) {
squared_x += x[i] * x[i];
squared_y += y[i] * y[i];
}
- if (squared_x == 0 or squared_y == 0) {
+
+ if (squared_x == 0 || squared_y == 0) {
return 2.0f;
}
- return 1 - dot_prod / sqrt(squared_x * squared_y);
+
+ // Accumulate the norm in double and take a single square root. Computing
+ // (double)squared_x * (double)squared_y cannot overflow for finite float
inputs,
+ // whereas the float expression sqrt(squared_x * squared_y) overflows to
+inf for
+ // large-magnitude vectors and would silently yield a distance of 1.0.
+ const double norm = std::sqrt(static_cast<double>(squared_x) *
static_cast<double>(squared_y));
+ // Clamp the cosine to [-1, 1] before mapping to a distance.
Floating-point rounding
+ // can push the ratio slightly outside [-1, 1] (e.g. 1.0000001 for
identical vectors),
+ // which would otherwise produce a tiny negative distance.
+ const float cosine = std::clamp(static_cast<float>(dot_prod / norm),
-1.0f, 1.0f);
+ return 1.0f - cosine;
}
FAISS_PRAGMA_IMPRECISE_FUNCTION_END
FAISS_PRAGMA_IMPRECISE_FUNCTION_BEGIN
float CosineSimilarity::distance(const float* x, const float* y, size_t d) {
+ if (d == 0) {
+ return 0.0f;
+ }
+
+ DCHECK(x != nullptr && y != nullptr);
+
float dot_prod = 0;
Review Comment:
Thanks for the catch. The per-element overflow only triggers when |x[i]| >
sqrt(FLT_MAX) ≈ 1.84e19, which is even more pathological than the outer-product
overflow this PR addresses. Widening accumulators to double would halve SIMD
throughput (~5-20% end-to-end regression in vector search workloads) while only
covering a stricter subset of overflow scenarios that have never been observed
in real embeddings. We prefer to keep the current scope; happy to file a
follow-up if a real-world case is reported.
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