From ade77a5e0fa8f753769c7aa3323cafdac054d14c Mon Sep 17 00:00:00 2001
From: Jan Wassenberg <janwas@google.com>
Date: Thu, 9 Jan 2025 07:24:04 -0800
Subject: [PATCH] fix emu128 reduction with infinities. thanks @yohanchatelain,
 fixes #2434

PiperOrigin-RevId: 713663844
---
 hwy/ops/emu128-inl.h | 25 +++++++++++++++++++++++--
 1 file changed, 23 insertions(+), 2 deletions(-)

diff --git a/hwy/ops/emu128-inl.h b/hwy/ops/emu128-inl.h
index 7a361de011..a530a8f9f6 100644
--- a/hwy/ops/emu128-inl.h
+++ b/hwy/ops/emu128-inl.h
@@ -2916,9 +2916,30 @@ HWY_API T ReduceSum(D d, VFromD<D> v) {
   }
   return sum;
 }
+
+namespace detail {
+template <class D, typename T = TFromD<D>, HWY_IF_FLOAT_OR_SPECIAL(T)>
+T InitReduceMin(D d) {
+  return GetLane(Inf(d));
+}
+template <class D, typename T = TFromD<D>, HWY_IF_NOT_FLOAT_NOR_SPECIAL(T)>
+T InitReduceMin(D d) {
+  return HighestValue<T>();
+}
+
+template <class D, typename T = TFromD<D>, HWY_IF_FLOAT_OR_SPECIAL(T)>
+T InitReduceMax(D d) {
+  return -GetLane(Inf(d));
+}
+template <class D, typename T = TFromD<D>, HWY_IF_NOT_FLOAT_NOR_SPECIAL(T)>
+T InitReduceMax(D d) {
+  return LowestValue<T>();
+}
+}  // namespace detail
+
 template <class D, typename T = TFromD<D>, HWY_IF_REDUCE_D(D)>
 HWY_API T ReduceMin(D d, VFromD<D> v) {
-  T min = HighestValue<T>();
+  T min = detail::InitReduceMin(d);
   for (size_t i = 0; i < MaxLanes(d); ++i) {
     min = HWY_MIN(min, v.raw[i]);
   }
@@ -2926,7 +2947,7 @@ HWY_API T ReduceMin(D d, VFromD<D> v) {
 }
 template <class D, typename T = TFromD<D>, HWY_IF_REDUCE_D(D)>
 HWY_API T ReduceMax(D d, VFromD<D> v) {
-  T max = LowestValue<T>();
+  T max = detail::InitReduceMax(d);
   for (size_t i = 0; i < MaxLanes(d); ++i) {
     max = HWY_MAX(max, v.raw[i]);
   }