blob: 5deb6217278a457c0984d4a096d18dc851dd5d1b [file] [log] [blame]
 /* * Copyright (c) 2015 The WebRTC project authors. All Rights Reserved. * * Use of this source code is governed by a BSD-style license * that can be found in the LICENSE file in the root of the source * tree. An additional intellectual property rights grant can be found * in the file PATENTS. All contributing project authors may * be found in the AUTHORS file in the root of the source tree. */ #include "rtc_base/random.h" #include #include "rtc_base/checks.h" #include "rtc_base/numerics/safe_conversions.h" namespace webrtc { Random::Random(uint64_t seed) { RTC_DCHECK(seed != 0x0ull); state_ = seed; } uint32_t Random::Rand(uint32_t t) { // Casting the output to 32 bits will give an almost uniform number. // Pr[x=0] = (2^32-1) / (2^64-1) // Pr[x=k] = 2^32 / (2^64-1) for k!=0 // Uniform would be Pr[x=k] = 2^32 / 2^64 for all 32-bit integers k. uint32_t x = NextOutput(); // If x / 2^32 is uniform on [0,1), then x / 2^32 * (t+1) is uniform on // the interval [0,t+1), so the integer part is uniform on [0,t]. uint64_t result = x * (static_cast(t) + 1); result >>= 32; return result; } uint32_t Random::Rand(uint32_t low, uint32_t high) { RTC_DCHECK(low <= high); return Rand(high - low) + low; } int32_t Random::Rand(int32_t low, int32_t high) { RTC_DCHECK(low <= high); const int64_t low_i64{low}; return rtc::dchecked_cast( Rand(rtc::dchecked_cast(high - low_i64)) + low_i64); } template <> float Random::Rand() { double result = NextOutput() - 1; result = result / 0xFFFFFFFFFFFFFFFEull; return static_cast(result); } template <> double Random::Rand() { double result = NextOutput() - 1; result = result / 0xFFFFFFFFFFFFFFFEull; return result; } template <> bool Random::Rand() { return Rand(0, 1) == 1; } double Random::Gaussian(double mean, double standard_deviation) { // Creating a Normal distribution variable from two independent uniform // variables based on the Box-Muller transform, which is defined on the // interval (0, 1]. Note that we rely on NextOutput to generate integers // in the range [1, 2^64-1]. Normally this behavior is a bit frustrating, // but here it is exactly what we need. const double kPi = 3.14159265358979323846; double u1 = static_cast(NextOutput()) / 0xFFFFFFFFFFFFFFFFull; double u2 = static_cast(NextOutput()) / 0xFFFFFFFFFFFFFFFFull; return mean + standard_deviation * sqrt(-2 * log(u1)) * cos(2 * kPi * u2); } double Random::Exponential(double lambda) { double uniform = Rand(); return -log(uniform) / lambda; } } // namespace webrtc