1 files changed, 59 insertions, 0 deletions
diff --git a/tensorflow/compiler/xla/service/llvm_ir/math_ops.cc b/tensorflow/compiler/xla/service/llvm_ir/math_ops.cc
new file mode 100644
index 0000000000..0e115cdabf
--- /dev/null
+++ b/tensorflow/compiler/xla/service/llvm_ir/math_ops.cc
@@ -0,0 +1,59 @@
+/* Copyright 2018 The TensorFlow Authors. All Rights Reserved.
+
+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.
+==============================================================================*/
+
+#include "tensorflow/compiler/xla/service/llvm_ir/math_ops.h"
+#include "tensorflow/compiler/xla/service/llvm_ir/llvm_util.h"
+
+namespace xla {
+namespace llvm_ir {
+
+llvm::Value* EmitFastTanh(llvm::IRBuilder<>* b, llvm::Value* input) {
+  llvm::Type* type = input->getType();
+
+  // Clamp the input to [-9, 9].
+  llvm::Value* input_clamped = llvm_ir::EmitFloatMin(
+      llvm_ir::EmitFloatMax(input, llvm::ConstantFP::get(type, -9.0), b),
+      llvm::ConstantFP::get(type, 9.0), b);
+
+  static constexpr std::array<float, 7> numerator_coeffs{
+      -2.76076847742355e-16f, 2.00018790482477e-13f, -8.60467152213735e-11f,
+      5.12229709037114e-08f,  1.48572235717979e-05f, 6.37261928875436e-04f,
+      4.89352455891786e-03f};
+
+  static constexpr std::array<float, 4> denominator_coeffs{
+      1.19825839466702e-06f, 1.18534705686654e-04f, 2.26843463243900e-03f,
+      4.89352518554385e-03f};
+
+  llvm::Value* input_squared = b->CreateFMul(input_clamped, input_clamped);
+  llvm::Value* numerator = llvm::ConstantFP::get(type, numerator_coeffs[0]);
+  for (int i = 1; i < numerator_coeffs.size(); i++) {
+    numerator = b->CreateFAdd(b->CreateFMul(input_squared, numerator),
+                              llvm::ConstantFP::get(type, numerator_coeffs[i]));
+  }
+
+  numerator = b->CreateFMul(input_clamped, numerator);
+
+  llvm::Value* denominator = llvm::ConstantFP::get(type, denominator_coeffs[0]);
+  for (int i = 1; i < denominator_coeffs.size(); i++) {
+    denominator =
+        b->CreateFAdd(b->CreateFMul(input_squared, denominator),
+                      llvm::ConstantFP::get(type, denominator_coeffs[i]));
+  }
+
+  return b->CreateFDiv(numerator, denominator);
+}
+
+}  // namespace llvm_ir
+}  // namespace xla