diff options
Diffstat (limited to 'src/leveldb/util/random.h')
-rw-r--r-- | src/leveldb/util/random.h | 59 |
1 files changed, 0 insertions, 59 deletions
diff --git a/src/leveldb/util/random.h b/src/leveldb/util/random.h deleted file mode 100644 index 07538242e..000000000 --- a/src/leveldb/util/random.h +++ /dev/null @@ -1,59 +0,0 @@ -// Copyright (c) 2011 The LevelDB Authors. All rights reserved. -// Use of this source code is governed by a BSD-style license that can be -// found in the LICENSE file. See the AUTHORS file for names of contributors. - -#ifndef STORAGE_LEVELDB_UTIL_RANDOM_H_ -#define STORAGE_LEVELDB_UTIL_RANDOM_H_ - -#include <stdint.h> - -namespace leveldb { - -// A very simple random number generator. Not especially good at -// generating truly random bits, but good enough for our needs in this -// package. -class Random { - private: - uint32_t seed_; - public: - explicit Random(uint32_t s) : seed_(s & 0x7fffffffu) { } - uint32_t Next() { - static const uint32_t M = 2147483647L; // 2^31-1 - static const uint64_t A = 16807; // bits 14, 8, 7, 5, 2, 1, 0 - // We are computing - // seed_ = (seed_ * A) % M, where M = 2^31-1 - // - // seed_ must not be zero or M, or else all subsequent computed values - // will be zero or M respectively. For all other values, seed_ will end - // up cycling through every number in [1,M-1] - uint64_t product = seed_ * A; - - // Compute (product % M) using the fact that ((x << 31) % M) == x. - seed_ = static_cast<uint32_t>((product >> 31) + (product & M)); - // The first reduction may overflow by 1 bit, so we may need to - // repeat. mod == M is not possible; using > allows the faster - // sign-bit-based test. - if (seed_ > M) { - seed_ -= M; - } - return seed_; - } - // Returns a uniformly distributed value in the range [0..n-1] - // REQUIRES: n > 0 - uint32_t Uniform(int n) { return Next() % n; } - - // Randomly returns true ~"1/n" of the time, and false otherwise. - // REQUIRES: n > 0 - bool OneIn(int n) { return (Next() % n) == 0; } - - // Skewed: pick "base" uniformly from range [0,max_log] and then - // return "base" random bits. The effect is to pick a number in the - // range [0,2^max_log-1] with exponential bias towards smaller numbers. - uint32_t Skewed(int max_log) { - return Uniform(1 << Uniform(max_log + 1)); - } -}; - -} // namespace leveldb - -#endif // STORAGE_LEVELDB_UTIL_RANDOM_H_ |