Add dot product implementation for Intel FMA (double = tessdata_best)

Signed-off-by: Stefan Weil <sw@weilnetz.de>

CMakeLists.txt

@@ -220,6 +220,7 @@ endforeach()
 # add definition as expected in src/arch/simddetect.cpp
 set(AVX_OPT OFF)
 set(AVX2_OPT OFF)
+set(FMA_OPT OFF)
 set(SSE41_OPT OFF)
 set(MARCH_NATIVE_OPT OFF)
 foreach(flag ${_enable_vector_unit_list})  # from OptimizeForArchitecture()
@@ -227,7 +228,7 @@ foreach(flag ${_enable_vector_unit_list})  # from OptimizeForArchitecture()
     string(REPLACE "\." "_" flag "${flag}")
     set(sim_flags "${sim_flags} -D${flag}")
     string(REPLACE "_" "" flag "${flag}")
-    if("${flag}" MATCHES "AVX|AVX2|SSE41")
+    if("${flag}" MATCHES "AVX|AVX2|FMA|SSE41")
         set("${flag}_OPT" ON)
     endif()
 endforeach(flag)
@@ -285,6 +286,7 @@ message( STATUS "Architecture flags: ${Vc_ARCHITECTURE_FLAGS}")
 message( STATUS "Vector unit list: ${_enable_vector_unit_list}")
 message( STATUS "AVX_OPT: ${AVX_OPT}")
 message( STATUS "AVX2_OPT: ${AVX2_OPT}")
+message( STATUS "FMA_OPT: ${FMA_OPT}")
 message( STATUS "SSE41_OPT: ${SSE41_OPT}")
 message( STATUS "MARCH_NATIVE_OPT: ${MARCH_NATIVE_OPT}")
 message( STATUS "sim_flags: ${sim_flags}")
@@ -364,6 +366,9 @@ endif(AVX_OPT)
 if(AVX2_OPT)
    list(APPEND tesseract_src src/arch/intsimdmatrixavx2.cpp)
 endif(AVX2_OPT)
+if(FMA_OPT)
+   list(APPEND tesseract_src src/arch/dotproductfma.cpp)
+endif(AVX_OPT)
 if(SSE41_OPT)
    list(APPEND tesseract_src src/arch/dotproductsse.cpp src/arch/intsimdmatrixsse.cpp)
 endif(SSE41_OPT)

configure.ac

@@ -126,6 +126,9 @@ AM_CONDITIONAL([AVX_OPT], ${avx})
 AX_CHECK_COMPILE_FLAG([-mavx2], [avx2=true], [avx2=false], [$WERROR])
 AM_CONDITIONAL([AVX2_OPT], $avx2)
 
+AX_CHECK_COMPILE_FLAG([-mfma], [fma=true], [fma=false], [$WERROR])
+AM_CONDITIONAL([FMA_OPT], $fma)
+
 AX_CHECK_COMPILE_FLAG([-msse4.1], [sse41=true], [sse41=false], [$WERROR])
 AM_CONDITIONAL([SSE41_OPT], $sse41)
 

src/api/Makefile.am

@@ -68,6 +68,9 @@ endif
 if AVX2_OPT
 libtesseract_la_LIBADD += ../arch/libtesseract_avx2.la
 endif
+if FMA_OPT
+libtesseract_la_LIBADD += ../arch/libtesseract_fma.la
+endif
 if SSE41_OPT
 libtesseract_la_LIBADD += ../arch/libtesseract_sse.la
 endif

src/api/tesseractmain.cpp

@@ -136,6 +136,7 @@ static void PrintVersionInfo() {
   if (tesseract::SIMDDetect::IsAVX512FAvailable()) printf(" Found AVX512F\n");
   if (tesseract::SIMDDetect::IsAVX2Available()) printf(" Found AVX2\n");
   if (tesseract::SIMDDetect::IsAVXAvailable()) printf(" Found AVX\n");
+  if (tesseract::SIMDDetect::IsFMAAvailable()) printf(" Found FMA\n");
   if (tesseract::SIMDDetect::IsSSEAvailable()) printf(" Found SSE\n");
 #ifdef _OPENMP
   printf(" Found OpenMP %d\n", _OPENMP);

src/arch/Makefile.am

@@ -20,6 +20,9 @@ endif
 if AVX2_OPT
 noinst_LTLIBRARIES += libtesseract_avx2.la
 endif
+if FMA_OPT
+noinst_LTLIBRARIES += libtesseract_fma.la
+endif
 if SSE41_OPT
 noinst_LTLIBRARIES += libtesseract_sse.la
 endif
@@ -34,6 +37,10 @@ if AVX2_OPT
 libtesseract_arch_la_CPPFLAGS += -DAVX2
 libtesseract_avx2_la_CXXFLAGS = -mavx2
 endif
+if FMA_OPT
+libtesseract_arch_la_CPPFLAGS += -DFMA
+libtesseract_fma_la_CXXFLAGS = -mfma
+endif
 if SSE41_OPT
 libtesseract_arch_la_CPPFLAGS += -DSSE4_1
 libtesseract_sse_la_CXXFLAGS = -msse4.1
@@ -55,6 +62,10 @@ if AVX2_OPT
 libtesseract_avx2_la_SOURCES = intsimdmatrixavx2.cpp
 endif
 
+if FMA_OPT
+libtesseract_fma_la_SOURCES = dotproductfma.cpp
+endif
+
 if SSE41_OPT
 libtesseract_sse_la_SOURCES = dotproductsse.cpp intsimdmatrixsse.cpp
 endif

src/arch/dotproduct.h

@@ -22,6 +22,9 @@ namespace tesseract {
 // Computes and returns the dot product of the n-vectors u and v.
 double DotProductNative(const double* u, const double* v, int n);
 
+// Use Intel FMA.
+double DotProductFMA(const double* u, const double* v, int n);
+
 }  // namespace tesseract.
 
 #endif  // TESSERACT_ARCH_DOTPRODUCT_H_

src/arch/dotproductfma.cpp

@@ -0,0 +1,57 @@
+///////////////////////////////////////////////////////////////////////
+// File:        dotproductfma.cpp
+// Description: Architecture-specific dot-product function.
+// Author:      Stefan Weil
+//
+// (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(__FMA__)
+#error Implementation only for FMA capable architectures
+#endif
+
+#include <immintrin.h>
+#include <cstdint>
+#include "dotproduct.h"
+
+namespace tesseract {
+
+// Computes and returns the dot product of the n-vectors u and v.
+// Uses Intel FMA intrinsics to access the SIMD instruction set.
+double DotProductFMA(const double* u, const double* v, int n) {
+  const unsigned quot = n / 8;
+  const unsigned rem = n % 8;
+  __m256d t0 = _mm256_setzero_pd();
+  __m256d t1 = _mm256_setzero_pd();
+  for (unsigned k = 0; k < quot; k++) {
+    __m256d f0 = _mm256_loadu_pd(u);
+    __m256d f1 = _mm256_loadu_pd(v);
+    t0 = _mm256_fmadd_pd(f0, f1, t0);
+    u += 4;
+    v += 4;
+    __m256d f2 = _mm256_loadu_pd(u);
+    __m256d f3 = _mm256_loadu_pd(v);
+    t1 = _mm256_fmadd_pd(f2, f3, t1);
+    u += 4;
+    v += 4;
+  }
+  t0 = _mm256_hadd_pd(t0, t1);
+  alignas(32) double tmp[4];
+  _mm256_store_pd(tmp, t0);
+  double result = tmp[0] + tmp[1] + tmp[2] + tmp[3];
+  for (unsigned k = 0; k < rem; k++) {
+    result += *u++ * *v++;
+  }
+  return result;
+}
+
+}  // namespace tesseract.

src/arch/simddetect.cpp

@@ -24,7 +24,7 @@
 #include "params.h"   // for STRING_VAR
 #include "tprintf.h"  // for tprintf
 
-#if defined(AVX) || defined(AVX2) || defined(SSE4_1)
+#if defined(AVX) || defined(AVX2) || defined(FMA) || defined(SSE4_1)
 # define HAS_CPUID
 #endif
 
@@ -60,6 +60,8 @@ bool SIMDDetect::avx_available_;
 bool SIMDDetect::avx2_available_;
 bool SIMDDetect::avx512F_available_;
 bool SIMDDetect::avx512BW_available_;
+// If true, then FMA has been detected.
+bool SIMDDetect::fma_available_;
 // If true, then SSe4.1 has been detected.
 bool SIMDDetect::sse_available_;
 
@@ -98,6 +100,9 @@ SIMDDetect::SIMDDetect() {
 #if defined(SSE4_1)
     sse_available_ = (ecx & 0x00080000) != 0;
 #endif
+#if defined(FMA)
+    fma_available_ = (ecx & 0x00001000) != 0;
+#endif
 #if defined(AVX)
     avx_available_ = (ecx & 0x10000000) != 0;
     if (avx_available_) {
@@ -121,6 +126,9 @@ SIMDDetect::SIMDDetect() {
 #if defined(SSE4_1)
     sse_available_ = (cpuInfo[2] & 0x00080000) != 0;
 #endif
+#if defined(FMA)
+    fma_available_ = (cpuInfo[2] & 0x00001000) != 0;
+#endif
 #if defined(AVX)
     avx_available_ = (cpuInfo[2] & 0x10000000) != 0;
 #endif
@@ -185,6 +193,12 @@ void SIMDDetect::Update() {
     SetDotProduct(DotProductAVX, &IntSimdMatrix::intSimdMatrixSSE);
     dotproduct_method = "avx";
 #endif
+#if defined(FMA)
+  } else if (!strcmp(dotproduct.string(), "fma")) {
+    // FMA selected by config variable.
+    SetDotProduct(DotProductFMA, IntSimdMatrix::intSimdMatrix);
+    dotproduct_method = "fma";
+#endif
 #if defined(SSE4_1)
   } else if (!strcmp(dotproduct.string(), "sse")) {
     // SSE selected by config variable.

src/arch/simddetect.h

@@ -46,6 +46,10 @@ class SIMDDetect {
   static inline bool IsAVX512BWAvailable() {
     return detector.avx512BW_available_;
   }
+  // Returns true if FMA is available on this system.
+  static inline bool IsFMAAvailable() {
+    return detector.fma_available_;
+  }
   // Returns true if SSE4.1 is available on this system.
   static inline bool IsSSEAvailable() {
     return detector.sse_available_;
@@ -66,6 +70,8 @@ class SIMDDetect {
   static TESS_API bool avx2_available_;
   static TESS_API bool avx512F_available_;
   static TESS_API bool avx512BW_available_;
+  // If true, then FMA has been detected.
+  static TESS_API bool fma_available_;
   // If true, then SSe4.1 has been detected.
   static TESS_API bool sse_available_;
 };