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Implement DotProductSSE() for FAST_FLOAT

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Ger Hobbelt 2021-07-13 09:20:39 +02:00 committed by Stefan Weil
parent 79e8b4f344
commit 27597883db
2 changed files with 59 additions and 7 deletions
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64
src/arch/dotproductsse.cpp
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@ -31,12 +31,63 @@ 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)
TFloat DotProductSSE(const TFloat *u, const TFloat *v, int n) {
TFloat total = 0.0;
for (int k = 0; k < n; ++k) {
total += u[k] * v[k];
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;
}
}
}
return total;
// 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) {
@ -48,7 +99,8 @@ double DotProductSSE(const double *u, const double *v, int n) {
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) {
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);

2
src/arch/intsimdmatrix.h
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@ -115,7 +115,7 @@ struct TESS_API IntSimdMatrix {
static const IntSimdMatrix *intSimdMatrix;
// Only available with NEON.
static const IntSimdMatrix intSimdMatrixNEON;
// Only available with AVX2 / SSE.
// Only available with AVX2 / AVX / FMA / SSE.
static const IntSimdMatrix intSimdMatrixAVX2;
static const IntSimdMatrix intSimdMatrixSSE;
};