X-Git-Url: http://plrg.eecs.uci.edu/git/?p=folly.git;a=blobdiff_plain;f=folly%2FRandom.h;h=e74d64b14dcf441c944483092f7a6b8491fb4f2d;hp=daa8e1e76bcaeea36f418a4a6fd27fe0f87fbe4c;hb=96ac8f8ff0c9bc9446eede119fdfee0fe7feaba3;hpb=22afce906d7e98d95f8c45c3301072d9fd891d41

diff --git a/folly/Random.h b/folly/Random.h
index daa8e1e7..e74d64b1 100644
--- a/folly/Random.h
+++ b/folly/Random.h
@@ -1,5 +1,5 @@
 /*
- * Copyright 2014 Facebook, Inc.
+ * Copyright 2017 Facebook, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -14,18 +14,286 @@
  * limitations under the License.
  */
 
-#ifndef FOLLY_BASE_RANDOM_H_
-#define FOLLY_BASE_RANDOM_H_
+#pragma once
+#define FOLLY_RANDOM_H_
 
-#include <stdint.h>
+#include <array>
+#include <cstdint>
+#include <random>
+#include <type_traits>
+
+#include <folly/Portability.h>
+#include <folly/Traits.h>
+
+#if FOLLY_HAVE_EXTRANDOM_SFMT19937
+#include <ext/random>
+#endif
 
 namespace folly {
 
+/**
+ * A PRNG with one instance per thread. This PRNG uses a mersenne twister random
+ * number generator and is seeded from /dev/urandom. It should not be used for
+ * anything which requires security, only for statistical randomness.
+ *
+ * An instance of this class represents the current threads PRNG. This means
+ * copying an instance of this class across threads will result in corruption
+ *
+ * Most users will use the Random class which implicitly creates this class.
+ * However, if you are worried about performance, you can memoize the TLS
+ * lookups that get the per thread state by manually using this class:
+ *
+ * ThreadLocalPRNG rng;
+ * for (...) {
+ *   Random::rand32(rng);
+ * }
+ */
+class ThreadLocalPRNG {
+ public:
+  typedef uint32_t result_type;
+
+  uint32_t operator()() {
+    // Using a static method allows the compiler to avoid allocating stack space
+    // for this class.
+    return getImpl(local_);
+  }
+
+  static constexpr result_type min() {
+    return std::numeric_limits<result_type>::min();
+  }
+  static constexpr result_type max() {
+    return std::numeric_limits<result_type>::max();
+  }
+  friend class Random;
+
+  ThreadLocalPRNG();
+
+  class LocalInstancePRNG;
+
+ private:
+  static result_type getImpl(LocalInstancePRNG* local);
+  LocalInstancePRNG* local_;
+};
+
+
+class Random {
+
+ private:
+  template <class RNG>
+  using ValidRNG = typename std::enable_if<
+      std::is_unsigned<typename std::result_of<RNG&()>::type>::value,
+      RNG>::type;
+
+ public:
+  // Default generator type.
+#if FOLLY_HAVE_EXTRANDOM_SFMT19937
+  typedef __gnu_cxx::sfmt19937 DefaultGenerator;
+#else
+  typedef std::mt19937 DefaultGenerator;
+#endif
+
+  /**
+   * Get secure random bytes. (On Linux and OSX, this means /dev/urandom).
+   */
+  static void secureRandom(void* data, size_t len);
+
+  /**
+   * Shortcut to get a secure random value of integral type.
+   */
+  template <class T>
+  static typename std::enable_if<
+    std::is_integral<T>::value && !std::is_same<T,bool>::value,
+    T>::type
+  secureRandom() {
+    T val;
+    secureRandom(&val, sizeof(val));
+    return val;
+  }
+
+  /**
+   * (Re-)Seed an existing RNG with a good seed.
+   *
+   * Note that you should usually use ThreadLocalPRNG unless you need
+   * reproducibility (such as during a test), in which case you'd want
+   * to create a RNG with a good seed in production, and seed it yourself
+   * in test.
+   */
+  template <class RNG = DefaultGenerator, class /* EnableIf */ = ValidRNG<RNG>>
+  static void seed(RNG& rng);
+
+  /**
+   * Create a new RNG, seeded with a good seed.
+   *
+   * Note that you should usually use ThreadLocalPRNG unless you need
+   * reproducibility (such as during a test), in which case you'd want
+   * to create a RNG with a good seed in production, and seed it yourself
+   * in test.
+   */
+  template <class RNG = DefaultGenerator, class /* EnableIf */ = ValidRNG<RNG>>
+  static RNG create();
+
+  /**
+   * Returns a random uint32_t
+   */
+  static uint32_t rand32() {
+    return rand32(ThreadLocalPRNG());
+  }
+
+  /**
+   * Returns a random uint32_t given a specific RNG
+   */
+  template <class RNG, class /* EnableIf */ = ValidRNG<RNG>>
+  static uint32_t rand32(RNG&& rng) {
+    return rng();
+  }
+
+  /**
+   * Returns a random uint32_t in [0, max). If max == 0, returns 0.
+   */
+  static uint32_t rand32(uint32_t max) {
+    return rand32(0, max, ThreadLocalPRNG());
+  }
+
+  /**
+   * Returns a random uint32_t in [0, max) given a specific RNG.
+   * If max == 0, returns 0.
+   */
+  template <class RNG = ThreadLocalPRNG, class /* EnableIf */ = ValidRNG<RNG>>
+  static uint32_t rand32(uint32_t max, RNG&& rng) {
+    return rand32(0, max, rng);
+  }
+
+  /**
+   * Returns a random uint32_t in [min, max). If min == max, returns 0.
+   */
+  static uint32_t rand32(uint32_t min, uint32_t max) {
+    return rand32(min, max, ThreadLocalPRNG());
+  }
+
+  /**
+   * Returns a random uint32_t in [min, max) given a specific RNG.
+   * If min == max, returns 0.
+   */
+  template <class RNG = ThreadLocalPRNG, class /* EnableIf */ = ValidRNG<RNG>>
+  static uint32_t rand32(uint32_t min, uint32_t max, RNG&& rng) {
+    if (min == max) {
+      return 0;
+    }
+    return std::uniform_int_distribution<uint32_t>(min, max - 1)(rng);
+  }
+
+  /**
+   * Returns a random uint64_t
+   */
+  static uint64_t rand64() {
+    return rand64(ThreadLocalPRNG());
+  }
+
+  /**
+   * Returns a random uint64_t
+   */
+  template <class RNG = ThreadLocalPRNG, class /* EnableIf */ = ValidRNG<RNG>>
+  static uint64_t rand64(RNG&& rng) {
+    return ((uint64_t)rng() << 32) | rng();
+  }
+
+  /**
+   * Returns a random uint64_t in [0, max). If max == 0, returns 0.
+   */
+  static uint64_t rand64(uint64_t max) {
+    return rand64(0, max, ThreadLocalPRNG());
+  }
+
+  /**
+   * Returns a random uint64_t in [0, max). If max == 0, returns 0.
+   */
+  template <class RNG = ThreadLocalPRNG, class /* EnableIf */ = ValidRNG<RNG>>
+  static uint64_t rand64(uint64_t max, RNG&& rng) {
+    return rand64(0, max, rng);
+  }
+
+  /**
+   * Returns a random uint64_t in [min, max). If min == max, returns 0.
+   */
+  static uint64_t rand64(uint64_t min, uint64_t max) {
+    return rand64(min, max, ThreadLocalPRNG());
+  }
+
+  /**
+   * Returns a random uint64_t in [min, max). If min == max, returns 0.
+   */
+  template <class RNG = ThreadLocalPRNG, class /* EnableIf */ = ValidRNG<RNG>>
+  static uint64_t rand64(uint64_t min, uint64_t max, RNG&& rng) {
+    if (min == max) {
+      return 0;
+    }
+    return std::uniform_int_distribution<uint64_t>(min, max - 1)(rng);
+  }
+
+  /**
+   * Returns true 1/n of the time. If n == 0, always returns false
+   */
+  static bool oneIn(uint32_t n) {
+    return oneIn(n, ThreadLocalPRNG());
+  }
+
+  /**
+   * Returns true 1/n of the time. If n == 0, always returns false
+   */
+  template <class RNG = ThreadLocalPRNG, class /* EnableIf */ = ValidRNG<RNG>>
+  static bool oneIn(uint32_t n, RNG&& rng) {
+    if (n == 0) {
+      return false;
+    }
+    return rand32(0, n, rng) == 0;
+  }
+
+  /**
+   * Returns a double in [0, 1)
+   */
+  static double randDouble01() {
+    return randDouble01(ThreadLocalPRNG());
+  }
+
+  /**
+   * Returns a double in [0, 1)
+   */
+  template <class RNG = ThreadLocalPRNG, class /* EnableIf */ = ValidRNG<RNG>>
+  static double randDouble01(RNG&& rng) {
+    return std::generate_canonical<double, std::numeric_limits<double>::digits>(
+        rng);
+  }
+
+  /**
+    * Returns a double in [min, max), if min == max, returns 0.
+    */
+  static double randDouble(double min, double max) {
+    return randDouble(min, max, ThreadLocalPRNG());
+  }
+
+  /**
+    * Returns a double in [min, max), if min == max, returns 0.
+    */
+  template <class RNG = ThreadLocalPRNG, class /* EnableIf */ = ValidRNG<RNG>>
+  static double randDouble(double min, double max, RNG&& rng) {
+    if (std::fabs(max - min) < std::numeric_limits<double>::epsilon()) {
+      return 0;
+    }
+    return std::uniform_real_distribution<double>(min, max)(rng);
+  }
+
+};
+
 /*
  * Return a good seed for a random number generator.
+ * Note that this is a legacy function, as it returns a 32-bit value, which
+ * is too small to be useful as a "real" RNG seed. Use the functions in class
+ * Random instead.
  */
-uint32_t randomNumberSeed();
-
+inline uint32_t randomNumberSeed() {
+  return Random::rand32();
 }
 
-#endif
+} // namespace folly
+
+#include <folly/Random-inl.h>