From aa844899c937bde5d2b24f276b59997e5b668bde Mon Sep 17 00:00:00 2001 From: Abseil Team Date: Thu, 8 Aug 2019 10:56:58 -0700 Subject: Creation of LTS branch "lts_2019_08_08" - 9ee91d3e430fb33a4590486573792eb0fa146c2d Export of internal Abseil changes by Abseil Team - 8efba58a3b656e9b41fb0471ae6453425a61c520 Export of internal Abseil changes by Abseil Team - b49b8d16b67ec6912899684b732e6367f258cfdb Export of internal Abseil changes by Abseil Team - 67222ffc4c83d918ce8395aa61769eeb77df4c4d Export of internal Abseil changes by Abseil Team - c5c4db4f5191fe5e76cbf68dcc71fb28702f7d2b Export of internal Abseil changes by Abseil Team - 14550beb3b7b97195e483fb74b5efb906395c31e Export of internal Abseil changes. by Abseil Team - 52e88ee56b72cf32bc66534d942c7398ce481331 Export of internal Abseil changes. by Abseil Team - 36d37ab992038f52276ca66b9da80c1cf0f57dc2 Export of internal Abseil changes. by Abseil Team - ad1485c8986246b2ae9105e512738d0e97aec887 Export of internal Abseil changes. by Abseil Team - 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968a34ffdaadd7db062a9621dfbdf8b2d16e05af Export of internal Abseil changes. by Abseil Team - 3e2e9b5557e76d098de4b8a2a659125b98ca519b Merge pull request #231 from uilianries/feature/conan by Mark Barolak - 111ca7060a6ff50115ca85b59f6b5d8c8c5e9105 Export of internal Abseil changes. by Abseil Team - 389ec3f906f018661a5308458d623d01f96d7b23 Export of internal Abseil changes. by Abseil Team - 8fbcdb90952c57828c4a9c2f6d79fcd7cae9088f Export of internal Abseil changes. by Abseil Team - 455dc17ba1af9635f0b60155bc565bc572a1e722 Export of internal Abseil changes. by Abseil Team - f197d7c72a54064cfde5a2058f1513a4a0ee36fb Export of internal Abseil changes. by Abseil Team - 284378a71b32dfb3af4e3661f585e671d1b603a3 Export of internal Abseil changes. by Abseil Team GitOrigin-RevId: 9ee91d3e430fb33a4590486573792eb0fa146c2d Change-Id: Ia06e548bc106cc9d136f6c65714be6645317aced --- .../internal/gaussian_distribution_gentables.cc | 147 +++++++++++++++++++++ 1 file changed, 147 insertions(+) create mode 100644 absl/random/internal/gaussian_distribution_gentables.cc (limited to 'absl/random/internal/gaussian_distribution_gentables.cc') diff --git a/absl/random/internal/gaussian_distribution_gentables.cc b/absl/random/internal/gaussian_distribution_gentables.cc new file mode 100644 index 00000000..6f9a28be --- /dev/null +++ b/absl/random/internal/gaussian_distribution_gentables.cc @@ -0,0 +1,147 @@ +// Copyright 2017 The Abseil Authors. +// +// 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 +// +// https://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. + +// Generates gaussian_distribution.cc +// +// $ blaze run :gaussian_distribution_gentables > gaussian_distribution.cc +// +#include "absl/random/gaussian_distribution.h" + +#include +#include +#include +#include +#include + +#include "absl/base/macros.h" + +namespace absl { +inline namespace lts_2019_08_08 { +namespace random_internal { +namespace { + +template +void FormatArrayContents(std::ostream* os, T (&data)[N]) { + if (!std::numeric_limits::is_exact) { + // Note: T is either an integer or a float. + // float requires higher precision to ensure that values are + // reproduced exactly. + // Trivia: C99 has hexadecimal floating point literals, but C++11 does not. + // Using them would remove all concern of precision loss. + os->precision(std::numeric_limits::max_digits10 + 2); + } + *os << " {"; + std::string separator = ""; + for (size_t i = 0; i < N; ++i) { + *os << separator << data[i]; + if ((i + 1) % 3 != 0) { + separator = ", "; + } else { + separator = ",\n "; + } + } + *os << "}"; +} + +} // namespace + +class TableGenerator : public gaussian_distribution_base { + public: + TableGenerator(); + void Print(std::ostream* os); + + using gaussian_distribution_base::kMask; + using gaussian_distribution_base::kR; + using gaussian_distribution_base::kV; + + private: + Tables tables_; +}; + +// Ziggurat gaussian initialization. For an explanation of the algorithm, see +// the Marsaglia paper, "The Ziggurat Method for Generating Random Variables". +// http://www.jstatsoft.org/v05/i08/ +// +// Further details are available in the Doornik paper +// https://www.doornik.com/research/ziggurat.pdf +// +TableGenerator::TableGenerator() { + // The constants here should match the values in gaussian_distribution.h + static constexpr int kC = kMask + 1; + + static_assert((ABSL_ARRAYSIZE(tables_.x) == kC + 1), + "xArray must be length kMask + 2"); + + static_assert((ABSL_ARRAYSIZE(tables_.x) == ABSL_ARRAYSIZE(tables_.f)), + "fx and x arrays must be identical length"); + + auto f = [](double x) { return std::exp(-0.5 * x * x); }; + auto f_inv = [](double x) { return std::sqrt(-2.0 * std::log(x)); }; + + tables_.x[0] = kV / f(kR); + tables_.f[0] = f(tables_.x[0]); + + tables_.x[1] = kR; + tables_.f[1] = f(tables_.x[1]); + + tables_.x[kC] = 0.0; + tables_.f[kC] = f(tables_.x[kC]); // 1.0 + + for (int i = 2; i < kC; i++) { + double v = (kV / tables_.x[i - 1]) + tables_.f[i - 1]; + tables_.x[i] = f_inv(v); + tables_.f[i] = v; + } +} + +void TableGenerator::Print(std::ostream* os) { + *os << "// BEGIN GENERATED CODE; DO NOT EDIT\n" + "// clang-format off\n" + "\n" + "#include \"absl/random/gaussian_distribution.h\"\n" + "\n" + // "namespace " and "absl" are broken apart so as not to conflict with + // script that adds the LTS inline namespace. + "namespace " + "absl {\n" + "namespace " + "random_internal {\n" + "\n" + "const gaussian_distribution_base::Tables\n" + " gaussian_distribution_base::zg_ = {\n"; + FormatArrayContents(os, tables_.x); + *os << ",\n"; + FormatArrayContents(os, tables_.f); + *os << "};\n" + "\n" + "} // namespace " + "random_internal\n" + "} // namespace " + "absl\n" + "\n" + "// clang-format on\n" + "// END GENERATED CODE"; + *os << std::endl; +} + +} // namespace random_internal +} // inline namespace lts_2019_08_08 +} // namespace absl + +int main(int, char**) { + std::cerr << "\nCopy the output to gaussian_distribution.cc" << std::endl; + absl::random_internal::TableGenerator generator; + generator.Print(&std::cout); + return 0; +} -- cgit v1.2.3