From 2985958d1d9554789c5cc3004c162d43ad80e361 Mon Sep 17 00:00:00 2001
From: Kenneth Heafield <kheafiel@amazon.com>
Date: Mon, 24 Feb 2020 17:41:29 +0000
Subject: MaxAbsolute with arbitrary many arguments

---
 multiply.h            | 26 +++++++++++++++++---------
 test/multiply_test.cc | 24 +++++++++++++-----------
 2 files changed, 30 insertions(+), 20 deletions(-)

diff --git a/multiply.h b/multiply.h
index 0aa86aa..9a15e0e 100644
--- a/multiply.h
+++ b/multiply.h
@@ -562,20 +562,28 @@ INTGEMM_SSSE3 inline static void InnerINTGEMM_SSSE3(
 } \
 
 #define INTGEMM_MAXABSOLUTE(Register, target) \
-target static float MaxAbsolute(const float *begin_float, const float *end_float) { \
+target static inline float MaxAbsolute(const float *begin_float, const float *end_float) { \
   assert(end_float > begin_float); \
-  assert((end_float - begin_float) % (sizeof(Register) / sizeof(float)) == 0); \
+  assert(reinterpret_cast<uintptr_t>(begin_float) % sizeof(Register) == 0); \
   const Register *begin = reinterpret_cast<const Register*>(begin_float); \
-  const Register *end = reinterpret_cast<const Register*>(end_float); \
-  union {float f; int32_t i;} float_convert; \
-  float_convert.i = 0x7fffffff; \
-  Register and_me = set1_ps<Register>(float_convert.f); \
-  Register highest = and_ps(and_me, *begin); \
-  for (++begin; begin != end; ++begin) { \
+  const float *end_reg = end_float - (reinterpret_cast<uintptr_t>(end_float) % sizeof(Register)) / sizeof(float); \
+  const Register *end = reinterpret_cast<const Register*>(end_reg); \
+  union {float f; int32_t i;} and_convert, float_convert; \
+  and_convert.i = 0x7fffffff; \
+  Register and_me = set1_ps<Register>(and_convert.f); \
+  Register highest = setzero_ps<Register>(); \
+  for (; begin < end; ++begin) { \
     Register reg = and_ps(and_me, *begin); \
     highest = max_ps(highest, reg); \
   } \
-  return MaxFloat32(highest); \
+  float ret = MaxFloat32(highest); \
+  /* Overhang: this would be more efficient if done in a single SIMD operation with some zeroing */ \
+  for (const float *i = end_reg; i < end_float; ++i) { \
+    float_convert.f = *i; \
+    float_convert.i &= and_convert.i; \
+    ret = std::max(ret, float_convert.f); \
+  } \
+  return ret; \
 } \
 
 } // namespace intgemm
diff --git a/test/multiply_test.cc b/test/multiply_test.cc
index 59c62a9..97f68a3 100644
--- a/test/multiply_test.cc
+++ b/test/multiply_test.cc
@@ -194,18 +194,20 @@ void CompareMaxAbs(const float *begin, const float *end, float test) {
 template <float (*Backend) (const float *, const float *)> void TestMaxAbsolute() {
   std::mt19937 gen;
   std::uniform_real_distribution<float> dist(-8.0, 8.0);
-  AlignedVector<float> test(64);
-  // 64 tries.
-  for (int t = 0; t < 64; ++t) {
-    // Fill with [-8, 8).
-    for (auto& it : test) {
-      it = dist(gen);
+  const std::size_t kLengthMax = 65;
+  AlignedVector<float> test(kLengthMax);
+  for (std::size_t len = 1; len < kLengthMax; ++len) {
+    for (int t = 0; t < len; ++t) {
+      // Fill with [-8, 8).
+      for (auto& it : test) {
+        it = dist(gen);
+      }
+      CompareMaxAbs(test.begin(), test.begin() + len, Backend(test.begin(), test.begin() + len));
+      test[t] = -32.0;
+      CompareMaxAbs(test.begin(), test.begin() + len, Backend(test.begin(), test.begin() + len));
+      test[t] = 32.0;
+      CompareMaxAbs(test.begin(), test.begin() + len, Backend(test.begin(), test.begin() + len));
     }
-    CompareMaxAbs(test.begin(), test.end(), Backend(test.begin(), test.end()));
-    test[t] = -32.0;
-    CompareMaxAbs(test.begin(), test.end(), Backend(test.begin(), test.end()));
-    test[t] = 32.0;
-    CompareMaxAbs(test.begin(), test.end(), Backend(test.begin(), test.end()));
   }
 }
 
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