Add math function for sampling integers from:

1. uniform distribution
2. log uniform distribution

paddle/operators/math/sampler.cc

+#include "sampler.h"
+
+namespace paddle {
+namespace random {
+
+Sampler::~Sampler() {}
+
+UniformSampler::UniformSampler(int64 range)
+    : Sampler(range), inv_range_(1.0 / range) {
+  std::random_device r;
+  random_engine_ = std::make_shared<std::mt19937>(r());
+  dist_ = std::make_shared<std::uniform_int_distribution<>>(0, range);
+}
+
+int64 UniformSampler::Sample() const { return (*dist_)(*random_engine_); }
+
+float UniformSampler::Probability(int64 value) const { return inv_range_; }
+
+LogUniformSampler::LogUniformSampler(int64 range)
+    : Sampler(range), log_range_(log(range + 1)) {
+  std::random_device r;
+  random_engine_ = std::make_shared<std::mt19937>(r());
+  dist_ = std::make_shared<std::uniform_real_distribution<>>(0, 1);
+}
+
+int64 LogUniformSampler::Sample() const {
+  // Got Log Uniform distribution from uniform distribution by
+  // inverse_transform_sampling method
+  // More details:
+  // https://wanghaoshuang.github.io/2017/11/Log-uniform-distribution-sampler/
+  const int64 value =
+      static_cast<int64>(exp((*dist_)(*random_engine_) * log_range_)) - 1;
+  // Mathematically, value should be <= range_, but might not be due to some
+  // floating point roundoff, so we mod by range_.
+  return value % range_;
+}
+
+float LogUniformSampler::Probability(int64 value) const {
+  // Given f(x) = 1/[(x+1) * log_range_]
+  // The value's  probability  is integral of f(x) from value to (value + 1)
+  // More details:
+  // https://wanghaoshuang.github.io/2017/11/Log-uniform-distribution-sampler
+  return (log((value + 2.0) / (value + 1.0))) / log_range_;
+}
+
+}  // namespace random
+}  // namespace paddle

paddle/operators/math/sampler.h

+/* Copyright (c) 2016 PaddlePaddle Authors. All Rights Reserve.
+
+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. */
+
+#pragma once
+#include <memory>
+#include <random>
+typedef long int64;
+namespace paddle {
+namespace operators {
+namespace math {
+
+// TODO: Support for GPU
+
+/**
+* Sample integers from [0, range).
+*/
+class Sampler {
+ public:
+  explicit Sampler(int64 range) : range_(range) { /* check range > 0*/
+  }
+  virtual ~Sampler();
+  // Sample a single value
+  virtual int64 Sample() const = 0;
+  // The probability that a single call to Sample() returns the given value.
+  virtual float Probability(int64 value) const = 0;
+
+  int64 range() { return range_; };
+
+ protected:
+  const int64 range_;
+};
+
+/**
+ * Sample integers from [0, range).
+ * And the distribution function is:
+ * P(x) = 1 / range
+ */
+class UniformSampler : public Sampler {
+ public:
+  explicit UniformSampler(int64 range);
+
+  ~UniformSampler() override {}
+
+  int64 Sample() const override;
+
+  float Probability(int64 value) const override;
+
+ private:
+  const float inv_range_;
+  std::shared_ptr<std::mt19937_64> random_engine_;
+  std::shared_ptr<std::uniform_int_distribution<>> dist_;
+};
+
+/**
+ * Sample integers from [0, range).
+ * And the distribution function is:
+ * P(x) = (1/ln(range+1)) * ln(1 + 1/(x + 1))
+ */
+class LogUniformSampler : public Sampler {
+ public:
+  explicit LogUniformSampler(int64 range);
+
+  ~LogUniformSampler() override {}
+
+  int64 Sample() const override;
+
+  float Probability(int64 value) const override;
+
+ private:
+  const float log_range_;
+  std::shared_ptr<std::mt19937_64> random_engine_;
+  std::shared_ptr<std::uniform_real_distribution<>> dist_;
+};
+
+}  // math
+}  // namespace operators
+}  // namespace paddle