vowpalwabbit/rand48.cc


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//A quick implementation similar to drand48 for cross-platform compatibility
#include <stdint.h>
//
// NB: the 'ULL' suffix is not part of the constant it is there to
// prevent truncation of constant to (32-bit long) when compiling
// in a 32-bit env: warning: integer constant is too large for "long" type
//
#ifdef __clang__
#pragma clang diagnostic ignored "-Wc++11-long-long"
#endif
uint64_t a = 0xeece66d5deece66dULL;
uint64_t c = 2147483647;

int bias = 127 << 23;

float merand48(uint64_t& initial)
{
  initial = a * initial + c;
  int32_t temp = ((initial >> 25) & 0x7FFFFF) | bias;
  return *(float *)&temp - 1;
}

uint64_t v = c;

void msrand48(uint64_t initial) { v = initial; }

float frand48() { return merand48(v); }

float frand48_noadvance()
{
  uint64_t old_v = v;
  float ret = frand48();
  v = old_v;
  return ret;
}