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///////////////////////////////////////////////////////////////////////
// File: dotproductsse.cpp
// Description: Architecture-specific dot-product function.
// Author: Ray Smith
//
// (C) Copyright 2015, Google Inc.
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// http://www.apache.org/licenses/LICENSE-2.0
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
///////////////////////////////////////////////////////////////////////
#if !defined(__SSE4_1__)
/* willus mode -- don't throw an error -- just skip */
/*
# if defined(__i686__) || defined(__x86_64__)
# error Implementation only for SSE 4.1 capable architectures
# endif
*/
#else
# include <emmintrin.h>
# include <smmintrin.h>
# include <cstdint>
# include "dotproduct.h"
namespace tesseract {
// Computes and returns the dot product of the n-vectors u and v.
// Uses Intel SSE intrinsics to access the SIMD instruction set.
#if defined(FAST_FLOAT)
float DotProductSSE(const float *u, const float *v, int n) {
int max_offset = n - 4;
int offset = 0;
// Accumulate a set of 4 sums in sum, by loading pairs of 4 values from u and
// v, and multiplying them together in parallel.
__m128 sum = _mm_setzero_ps();
if (offset <= max_offset) {
offset = 4;
// Aligned load is reputedly faster but requires 16 byte aligned input.
if ((reinterpret_cast<uintptr_t>(u) & 15) == 0 &&
(reinterpret_cast<uintptr_t>(v) & 15) == 0) {
// Use aligned load.
sum = _mm_load_ps(u);
__m128 floats2 = _mm_load_ps(v);
// Multiply.
sum = _mm_mul_ps(sum, floats2);
while (offset <= max_offset) {
__m128 floats1 = _mm_load_ps(u + offset);
floats2 = _mm_load_ps(v + offset);
floats1 = _mm_mul_ps(floats1, floats2);
sum = _mm_add_ps(sum, floats1);
offset += 4;
}
} else {
// Use unaligned load.
sum = _mm_loadu_ps(u);
__m128 floats2 = _mm_loadu_ps(v);
// Multiply.
sum = _mm_mul_ps(sum, floats2);
while (offset <= max_offset) {
__m128 floats1 = _mm_loadu_ps(u + offset);
floats2 = _mm_loadu_ps(v + offset);
floats1 = _mm_mul_ps(floats1, floats2);
sum = _mm_add_ps(sum, floats1);
offset += 4;
}
}
}
// Add the 4 sums in sum horizontally.
#if 0
alignas(32) float tmp[4];
_mm_store_ps(tmp, sum);
float result = tmp[0] + tmp[1] + tmp[2] + tmp[3];
#else
__m128 zero = _mm_setzero_ps();
// https://www.felixcloutier.com/x86/haddps
sum = _mm_hadd_ps(sum, zero);
sum = _mm_hadd_ps(sum, zero);
// Extract the low result.
float result = _mm_cvtss_f32(sum);
#endif
// Add on any left-over products.
while (offset < n) {
result += u[offset] * v[offset];
++offset;
}
return result;
}
#else
double DotProductSSE(const double *u, const double *v, int n) {
int max_offset = n - 2;
int offset = 0;
// Accumulate a set of 2 sums in sum, by loading pairs of 2 values from u and
// v, and multiplying them together in parallel.
__m128d sum = _mm_setzero_pd();
if (offset <= max_offset) {
offset = 2;
// Aligned load is reputedly faster but requires 16 byte aligned input.
if ((reinterpret_cast<uintptr_t>(u) & 15) == 0 &&
(reinterpret_cast<uintptr_t>(v) & 15) == 0) {
// Use aligned load.
sum = _mm_load_pd(u);
__m128d floats2 = _mm_load_pd(v);
// Multiply.
sum = _mm_mul_pd(sum, floats2);
while (offset <= max_offset) {
__m128d floats1 = _mm_load_pd(u + offset);
floats2 = _mm_load_pd(v + offset);
offset += 2;
floats1 = _mm_mul_pd(floats1, floats2);
sum = _mm_add_pd(sum, floats1);
}
} else {
// Use unaligned load.
sum = _mm_loadu_pd(u);
__m128d floats2 = _mm_loadu_pd(v);
// Multiply.
sum = _mm_mul_pd(sum, floats2);
while (offset <= max_offset) {
__m128d floats1 = _mm_loadu_pd(u + offset);
floats2 = _mm_loadu_pd(v + offset);
offset += 2;
floats1 = _mm_mul_pd(floats1, floats2);
sum = _mm_add_pd(sum, floats1);
}
}
}
// Add the 2 sums in sum horizontally.
sum = _mm_hadd_pd(sum, sum);
// Extract the low result.
double result = _mm_cvtsd_f64(sum);
// Add on any left-over products.
while (offset < n) {
result += u[offset] * v[offset];
++offset;
}
return result;
}
#endif
} // namespace tesseract.
#endif
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