| /* |
| * Copyright (C) 2017 The Android Open Source Project |
| * |
| * 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. |
| */ |
| |
| // Fast approximation for exp. |
| |
| #ifndef LIBTEXTCLASSIFIER_UTIL_MATH_FASTEXP_H_ |
| #define LIBTEXTCLASSIFIER_UTIL_MATH_FASTEXP_H_ |
| |
| #include <cassert> |
| #include <cmath> |
| #include <limits> |
| |
| #include "util/base/casts.h" |
| #include "util/base/integral_types.h" |
| #include "util/base/logging.h" |
| |
| namespace libtextclassifier2 { |
| |
| class FastMathClass { |
| private: |
| static const int kBits = 7; |
| static const int kMask1 = (1 << kBits) - 1; |
| static const int kMask2 = 0xFF << kBits; |
| static constexpr float kLogBase2OfE = 1.44269504088896340736f; |
| |
| struct Table { |
| int32 exp1[1 << kBits]; |
| }; |
| |
| public: |
| float VeryFastExp2(float f) const { |
| TC_DCHECK_LE(fabs(f), 126); |
| const float g = f + (127 + (1 << (23 - kBits))); |
| const int32 x = bit_cast<int32>(g); |
| int32 ret = ((x & kMask2) << (23 - kBits)) |
| | cache_.exp1[x & kMask1]; |
| return bit_cast<float>(ret); |
| } |
| |
| float VeryFastExp(float f) const { |
| return VeryFastExp2(f * kLogBase2OfE); |
| } |
| |
| private: |
| static const Table cache_; |
| }; |
| |
| extern FastMathClass FastMathInstance; |
| |
| inline float VeryFastExp2(float f) { return FastMathInstance.VeryFastExp2(f); } |
| inline float VeryFastExp(float f) { return FastMathInstance.VeryFastExp(f); } |
| |
| } // namespace libtextclassifier2 |
| |
| #endif // LIBTEXTCLASSIFIER_UTIL_MATH_FASTEXP_H_ |