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/********************* */
/*! \file sampler.cpp
** \verbatim
** Top contributors (to current version):
** Andres Noetzli
** This file is part of the CVC4 project.
** Copyright (c) 2009-2020 by the authors listed in the file AUTHORS
** in the top-level source directory) and their institutional affiliations.
** All rights reserved. See the file COPYING in the top-level source
** directory for licensing information.\endverbatim
**
** \brief Sampler class that generates random values of different sorts
**
** The Sampler class can be used to generate random values of different sorts
** with biased and unbiased distributions.
**/
#include "util/sampler.h"
#include "base/check.h"
#include "util/bitvector.h"
namespace CVC4 {
BitVector Sampler::pickBvUniform(unsigned sz)
{
Random& rnd = Random::getRandom();
std::stringstream ss;
for (unsigned i = 0; i < sz; i++)
{
ss << (rnd.pickWithProb(0.5) ? "1" : "0");
}
return BitVector(ss.str(), 2);
}
FloatingPoint Sampler::pickFpUniform(unsigned e, unsigned s)
{
return FloatingPoint(e, s, pickBvUniform(e + s));
}
FloatingPoint Sampler::pickFpBiased(unsigned e, unsigned s)
{
// The biased generation of random FP values is inspired by
// PyMPF [0].
//
// [0] https://github.com/florianschanda/PyMPF
Random& rnd = Random::getRandom();
BitVector zero(1);
BitVector one(1, static_cast<unsigned int>(1));
BitVector sign(1);
BitVector exp(e);
BitVector sig(s - 1);
if (rnd.pickWithProb(probSpecial))
{
// Generate special values
uint64_t type = rnd.pick(0, 12);
switch (type)
{
// NaN
// sign = 1, exp = 11...11, sig = 11...11
case 0:
sign = one;
exp = BitVector::mkOnes(e);
sig = BitVector::mkOnes(s - 1);
break;
// +/- inf
// sign = x, exp = 11...11, sig = 00...00
case 1: sign = one; CVC4_FALLTHROUGH;
case 2: exp = BitVector::mkOnes(e); break;
// +/- zero
// sign = x, exp = 00...00, sig = 00...00
case 3: sign = one; CVC4_FALLTHROUGH;
case 4: break;
// +/- max subnormal
// sign = x, exp = 00...00, sig = 11...11
case 5: sign = one; CVC4_FALLTHROUGH;
case 6: sig = BitVector::mkOnes(s - 1); break;
// +/- min subnormal
// sign = x, exp = 00...00, sig = 00...01
case 7: sign = one; CVC4_FALLTHROUGH;
case 8: sig = BitVector(s - 1, static_cast<unsigned int>(1)); break;
// +/- max normal
// sign = x, exp = 11...10, sig = 11...11
case 9: sign = one; CVC4_FALLTHROUGH;
case 10:
exp = BitVector::mkOnes(e) - BitVector(e, static_cast<unsigned int>(1));
sig = BitVector::mkOnes(s - 1);
break;
// +/- min normal
// sign = x, exp = 00...01, sig = 00...00
case 11: sign = one; CVC4_FALLTHROUGH;
case 12: exp = BitVector(e, static_cast<unsigned int>(1)); break;
default: Unreachable();
}
}
else
{
// Generate normal and subnormal values
// 50% chance of positive/negative sign
if (rnd.pickWithProb(0.5))
{
sign = one;
}
uint64_t pattern = rnd.pick(0, 5);
switch (pattern)
{
case 0:
// sign = x, exp = xx...x0, sig = 11...11
exp = pickBvUniform(e - 1).concat(zero);
sig = BitVector::mkOnes(s - 1);
break;
case 1:
// sign = x, exp = xx...x0, sig = 00...00
exp = pickBvUniform(e - 1).concat(zero);
break;
case 2:
// sign = x, exp = 0x...x1, sig = 11...11
exp = zero.concat(pickBvUniform(e - 2).concat(one));
sig = BitVector::mkOnes(s - 1);
break;
case 3:
// sign = x, exp = xx...x0, sig = xx...xx
exp = pickBvUniform(e - 1).concat(zero);
sig = pickBvUniform(s - 1);
break;
case 4:
// sign = x, exp = 0x...x1, sig = xx...xx
exp = zero.concat(pickBvUniform(e - 2).concat(one));
sig = pickBvUniform(s - 1);
break;
case 5:
{
// sign = x, exp = xx...xx0xx...xx, sig = xx...xx
uint64_t lsbSize = rnd.pick(1, e - 2);
uint64_t msbSize = e - lsbSize - 1;
BitVector lsb = pickBvUniform(lsbSize);
BitVector msb = pickBvUniform(msbSize);
exp = msb.concat(zero.concat(lsb));
sig = pickBvUniform(s - 1);
break;
}
default: Unreachable();
}
}
BitVector bv = sign.concat(exp.concat(sig));
return FloatingPoint(e, s, bv);
}
} // namespace CVC4
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