shithub: femtolisp

ref: b9ba6323e01dccbfcae1226e77b8c9b9677e67a9
dir: /llt/random.c/

/*
  random numbers
*/
#include "llt.h"
#include "ieee754.h"
#include "mt19937ar.c"

double
rand_double()
{
	union ieee754_double d;

	d.ieee.mantissa0 = genrand_int32();
	d.ieee.mantissa1 = genrand_int32();
	d.ieee.negative = 0;
	d.ieee.exponent = IEEE754_DOUBLE_BIAS + 0; /* 2^0 */
	return d.d - 1.0;
}

float
rand_float()
{
	union ieee754_float f;

	f.ieee.mantissa = genrand_int32();
	f.ieee.negative = 0;
	f.ieee.exponent = IEEE754_FLOAT_BIAS + 0; /* 2^0 */
	return f.f - 1.0;
}

double
randn()
{
	double s, vre, vim, ure, uim;
	static double next = -42;

	if(next != -42){
		s = next;
		next = -42;
		return s;
	}
	do{
		ure = rand_double();
		uim = rand_double();
		vre = 2*ure - 1;
		vim = 2*uim - 1;
		s = vre*vre + vim*vim;
	}while(s >= 1);
	s = sqrt(-2*log(s)/s);
	next = s * vre;
	return s * vim;
}

void
randomize(void)
{
	uint64_t tm = i64time();
	init_by_array((uint32_t*)&tm, 2);
}