From 3c19c52ca0380bbbd032ba15cd9ff8143e4b7b8e Mon Sep 17 00:00:00 2001
From: Junjie Qi <jqi@meta.com>
Date: Mon, 13 Apr 2026 13:02:00 -0700
Subject: [PATCH] Use std:: qualified math functions to avoid float-to-double
 promotion (#5088)

Summary:
Pull Request resolved: https://github.com/facebookresearch/faiss/pull/5088

Fix 4 `performance-type-promotion-in-math-fn` lint warnings by using `std::floor`, `std::fabs`, and `std::pow` instead of the unqualified C versions. The unqualified versions promote `float` arguments to `double`, causing unnecessary precision loss and performance overhead. Also added missing `#include <cmath>` in `IndexIVFSpectralHash.cpp`.

Reviewed By: mnorris11

Differential Revision: D100576274

fbshipit-source-id: f491b1e9432a42f56a5660002f5b10ed0f594f4c
---
 faiss/IndexIVFSpectralHash.cpp | 3 ++-
 faiss/VectorTransform.cpp      | 4 ++--
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/faiss/IndexIVFSpectralHash.cpp b/faiss/IndexIVFSpectralHash.cpp
index f0e53d36e..523ef8afb 100644
--- a/faiss/IndexIVFSpectralHash.cpp
+++ b/faiss/IndexIVFSpectralHash.cpp
@@ -10,6 +10,7 @@
 #include <faiss/IndexIVFSpectralHash.h>
 
 #include <algorithm>
+#include <cmath>
 #include <cstdint>
 #include <memory>
 
@@ -159,7 +160,7 @@ void binarize_with_freq(
     memset(codes, 0, (nbit + 7) / 8);
     for (size_t i = 0; i < nbit; i++) {
         float xf = (x[i] - c[i]);
-        int64_t xi = int64_t(floor(xf * freq));
+        int64_t xi = int64_t(std::floor(xf * freq));
         int64_t bit = xi & 1;
         codes[i >> 3] |= bit << (i & 7);
     }
diff --git a/faiss/VectorTransform.cpp b/faiss/VectorTransform.cpp
index 0f5265f43..219920e88 100644
--- a/faiss/VectorTransform.cpp
+++ b/faiss/VectorTransform.cpp
@@ -279,7 +279,7 @@ void LinearTransform::set_is_orthonormal() {
                 float v = ATA[i + j * d_out];
                 if (i == j)
                     v -= 1;
-                if (fabs(v) > eps) {
+                if (std::fabs(v) > eps) {
                     is_orthonormal = false;
                 }
             }
@@ -773,7 +773,7 @@ void PCAMatrix::prepare_Ab() {
         if (eigen_power != 0) {
             float* ai = A.data();
             for (int i = 0; i < d_out; i++) {
-                float factor = pow(eigenvalues[i] + epsilon, eigen_power);
+                float factor = std::pow(eigenvalues[i] + epsilon, eigen_power);
                 for (int j = 0; j < d_in; j++)
                     *ai++ *= factor;
             }