leveldb::Random Class Reference

#include <random.h>

Public Member Functions
	Random (uint32_t s)
uint32_t	Next ()
uint32_t	Uniform (int n)
bool	OneIn (int n)
uint32_t	Skewed (int max_log)

Private Attributes
uint32_t	seed_

Detailed Description

Definition at line 15 of file random.h.

Constructor & Destructor Documentation

Random()

leveldb::Random::Random ( uint32_t  s )

inlineexplicit

Definition at line 19 of file random.h.

                              : seed_(s & 0x7fffffffu) {
    // Avoid bad seeds.
    if (seed_ == 0 || seed_ == 2147483647L) {
      seed_ = 1;
    }
  }

Member Function Documentation

Next()

uint32_t leveldb::Random::Next ( )

inline

Definition at line 25 of file random.h.

                  {
    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_;
  }

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OneIn()

bool leveldb::Random::OneIn ( int  n )

inline

Definition at line 52 of file random.h.

{ return (Next() % n) == 0; }

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Skewed()

uint32_t leveldb::Random::Skewed ( int  max_log )

inline

Definition at line 57 of file random.h.

                               {
    return Uniform(1 << Uniform(max_log + 1));
  }

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Uniform()

uint32_t leveldb::Random::Uniform ( int  n )

inline

Definition at line 48 of file random.h.

{ return Next() % n; }

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Member Data Documentation

seed_

uint32_t leveldb::Random::seed_

private

Definition at line 17 of file random.h.

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The documentation for this class was generated from the following file:

• util/random.h