framework/common/tcuFloatFormat.cpp

/*-------------------------------------------------------------------------
 * drawElements Quality Program Tester Core
 * ----------------------------------------
 *
 * Copyright 2014 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 *//*!
 * \file
 * \brief Adjustable-precision floating point operations.
 *//*--------------------------------------------------------------------*/

#include "tcuFloatFormat.hpp"

#include "deMath.h"
#include "deUniquePtr.hpp"

#include <sstream>
#include <iomanip>
#include <limits>

namespace tcu
{
namespace
{

Interval chooseInterval(YesNoMaybe choice, const Interval& no, const Interval& yes)
{
	switch (choice)
	{
		case NO:	return no;
		case YES:	return yes;
		case MAYBE:	return no | yes;
		default:	DE_FATAL("Impossible case");
	}

	return Interval();
}

double computeMaxValue (int maxExp, int fractionBits)
{
	return (deLdExp(1.0, maxExp) +
			deLdExp(double((1ull << fractionBits) - 1), maxExp - fractionBits));
}

} // anonymous

FloatFormat::FloatFormat (int			minExp,
						  int			maxExp,
						  int			fractionBits,
						  bool			exactPrecision,
						  YesNoMaybe	hasSubnormal_,
						  YesNoMaybe	hasInf_,
						  YesNoMaybe	hasNaN_)
	: m_minExp			(minExp)
	, m_maxExp			(maxExp)
	, m_fractionBits	(fractionBits)
	, m_hasSubnormal	(hasSubnormal_)
	, m_hasInf			(hasInf_)
	, m_hasNaN			(hasNaN_)
	, m_exactPrecision	(exactPrecision)
	, m_maxValue		(computeMaxValue(maxExp, fractionBits))
{
	DE_ASSERT(minExp <= maxExp);
}

/*-------------------------------------------------------------------------
 * On the definition of ULP
 *
 * The GLSL spec does not define ULP. However, it refers to IEEE 754, which
 * (reportedly) uses Harrison's definition:
 *
 * ULP(x) is the distance between the closest floating point numbers
 * a and be such that a <= x <= b and a != b
 *
 * Note that this means that when x = 2^n, ULP(x) = 2^(n-p-1), i.e. it is the
 * distance to the next lowest float, not next highest.
 *
 * Furthermore, it is assumed that ULP is calculated relative to the exact
 * value, not the approximation. This is because otherwise a less accurate
 * approximation could be closer in ULPs, because its ULPs are bigger.
 *
 * For details, see "On the definition of ulp(x)" by Jean-Michel Muller
 *
 *-----------------------------------------------------------------------*/

double FloatFormat::ulp (double x, double count) const
{
	int				exp		= 0;
	const double	frac	= deFractExp(deAbs(x), &exp);

	if (deIsNaN(frac))
		return TCU_NAN;
	else if (deIsInf(frac))
		return deLdExp(1.0, m_maxExp - m_fractionBits);
	else if (frac == 1.0)
	{
		// Harrison's ULP: choose distance to closest (i.e. next lower) at binade
		// boundary.
		--exp;
	}
	else if (frac == 0.0)
		exp = m_minExp;

	// ULP cannot be lower than the smallest quantum.
	exp = de::max(exp, m_minExp);

	{
		const double		oneULP	= deLdExp(1.0, exp - m_fractionBits);
		ScopedRoundingMode	ctx		(DE_ROUNDINGMODE_TO_POSITIVE_INF);

		return oneULP * count;
	}
}

//! Return the difference between the given nominal exponent and
//! the exponent of the lowest significand bit of the
//! representation of a number with this format.
//! For normal numbers this is the number of significand bits, but
//! for subnormals it is less and for values of exp where 2^exp is too
//! small to represent it is <0
int FloatFormat::exponentShift (int exp) const
{
	return m_fractionBits - de::max(m_minExp - exp, 0);
}

//! Return the number closest to `d` that is exactly representable with the
//! significand bits and minimum exponent of the floatformat. Round up if
//! `upward` is true, otherwise down.
double FloatFormat::round (double d, bool upward) const
{
	int				exp			= 0;
	const double	frac		= deFractExp(d, &exp);
	const int		shift		= exponentShift(exp);
	const double	shiftFrac	= deLdExp(frac, shift);
	const double	roundFrac	= upward ? deCeil(shiftFrac) : deFloor(shiftFrac);

	return deLdExp(roundFrac, exp - shift);
}

//! Return the range of numbers that `d` might be converted to in the
//! floatformat, given its limitations with infinities, subnormals and maximum
//! exponent.
Interval FloatFormat::clampValue (double d) const
{
	const double	rSign		= deSign(d);
	int				rExp		= 0;

	DE_ASSERT(!deIsNaN(d));

	deFractExp(d, &rExp);
	if (rExp < m_minExp)
		return chooseInterval(m_hasSubnormal, rSign * 0.0, d);
	else if (deIsInf(d) || rExp > m_maxExp)
		return chooseInterval(m_hasInf, rSign * getMaxValue(), rSign * TCU_INFINITY);

	return Interval(d);
}

//! Return the range of numbers that might be used with this format to
//! represent a number within `x`.
Interval FloatFormat::convert (const Interval& x) const
{
	Interval ret;
	Interval tmp = x;

	if (x.hasNaN())
	{
		// If NaN might be supported, NaN is a legal return value
		if (m_hasNaN != NO)
			ret |= TCU_NAN;

		// If NaN might not be supported, any (non-NaN) value is legal,
		// _subject_ to clamping. Hence we modify tmp, not ret.
		if (m_hasNaN != YES)
			tmp = Interval::unbounded();
	}

	// Round both bounds _inwards_ to closest representable values.
	if (!tmp.empty())
		ret |= clampValue(round(tmp.lo(), false)) | clampValue(round(tmp.hi(), true));

	// If this format's precision is not exact, the (possibly out-of-bounds)
	// original value is also a possible result.
	if (!m_exactPrecision)
		ret |= x;

	return ret;
}

double FloatFormat::roundOut (double d, bool upward, bool roundUnderOverflow) const
{
	int	exp	= 0;
	deFractExp(d, &exp);

	if (roundUnderOverflow && exp > m_maxExp && (upward == (d < 0.0)))
		return deSign(d) * getMaxValue();
	else
		return round(d, upward);
}

//! Round output of an operation.
//! \param roundUnderOverflow Can +/-inf rounded to min/max representable;
//!							  should be false if any of operands was inf, true otherwise.
Interval FloatFormat::roundOut (const Interval& x, bool roundUnderOverflow) const
{
	Interval ret = x.nan();

	if (!x.empty())
		ret |= Interval(roundOut(x.lo(), false, roundUnderOverflow),
						roundOut(x.hi(), true, roundUnderOverflow));

	return ret;
}

std::string	FloatFormat::floatToHex	(double x) const
{
	if (deIsNaN(x))
		return "NaN";
	else if (deIsInf(x))
		return (x < 0.0 ? "-" : "+") + std::string("inf");
	else if (x == 0.0) // \todo [2014-03-27 lauri] Negative zero
		return "0.0";

	int					exp			= 0;
	const double		frac		= deFractExp(deAbs(x), &exp);
	const int			shift		= exponentShift(exp);
	const deUint64		bits		= deUint64(deLdExp(frac, shift));
	const deUint64		whole		= bits >> m_fractionBits;
	const deUint64		fraction	= bits & ((deUint64(1) << m_fractionBits) - 1);
	const int			exponent	= exp + m_fractionBits - shift;
	const int			numDigits	= (m_fractionBits + 3) / 4;
	const deUint64		aligned		= fraction << (numDigits * 4 - m_fractionBits);
	std::ostringstream	oss;

	oss << (x < 0 ? "-" : "")
		<< "0x" << whole << "."
		<< std::hex << std::setw(numDigits) << std::setfill('0') << aligned
		<< "p" << std::dec << std::setw(0) << exponent;

	return oss.str();
}

std::string FloatFormat::intervalToHex (const Interval& interval) const
{
	if (interval.empty())
		return interval.hasNaN() ? "{ NaN }" : "{}";

	else if (interval.lo() == interval.hi())
		return (std::string(interval.hasNaN() ? "{ NaN, " : "{ ") +
				floatToHex(interval.lo()) + " }");
	else if (interval == Interval::unbounded(true))
		return "<any>";

	return (std::string(interval.hasNaN() ? "{ NaN } | " : "") +
			"[" + floatToHex(interval.lo()) + ", " + floatToHex(interval.hi()) + "]");
}

template <typename T>
static FloatFormat nativeFormat (void)
{
	typedef std::numeric_limits<T> Limits;

	DE_ASSERT(Limits::radix == 2);

	return FloatFormat(Limits::min_exponent - 1,	// These have a built-in offset of one
					   Limits::max_exponent - 1,
					   Limits::digits - 1,			// don't count the hidden bit
					   Limits::has_denorm != std::denorm_absent,
					   Limits::has_infinity ? YES : NO,
					   Limits::has_quiet_NaN ? YES : NO,
					   ((Limits::has_denorm == std::denorm_present) ? YES :
						(Limits::has_denorm == std::denorm_absent) ? NO :
						MAYBE));
}

FloatFormat	FloatFormat::nativeFloat (void)
{
	return nativeFormat<float>();
}

FloatFormat	FloatFormat::nativeDouble (void)
{
	return nativeFormat<double>();
}

namespace
{

using std::string;
using std::ostringstream;
using de::MovePtr;
using de::UniquePtr;

class Test
{
protected:

							Test		(MovePtr<FloatFormat> fmt) : m_fmt(fmt) {}
	double					p			(int e) const				{ return deLdExp(1.0, e); }
	void					check		(const string&	expr,
										 double			result,
										 double			reference) const;
	void					testULP		(double arg, double ref) const;
	void					testRound	(double arg, double refDown, double refUp) const;

	UniquePtr<FloatFormat>	m_fmt;
};

void Test::check (const string& expr, double result, double reference) const
{
	if (result != reference)
	{
		ostringstream oss;
		oss << expr << " returned " << result << ", expected " << reference;
		TCU_FAIL(oss.str().c_str());
	}
}

void Test::testULP (double arg, double ref) const
{
	ostringstream	oss;

	oss << "ulp(" << arg << ")";
	check(oss.str(), m_fmt->ulp(arg), ref);
}

void Test::testRound (double arg, double refDown, double refUp) const
{
	{
		ostringstream oss;
		oss << "round(" << arg << ", false)";
		check(oss.str(), m_fmt->round(arg, false), refDown);
	}
	{
		ostringstream oss;
		oss << "round(" << arg << ", true)";
		check(oss.str(), m_fmt->round(arg, true), refUp);
	}
}

class TestBinary32 : public Test
{
public:
			TestBinary32 (void)
				: Test (MovePtr<FloatFormat>(new FloatFormat(-126, 127, 23, true))) {}

	void	runTest	(void) const;
};

void TestBinary32::runTest (void) const
{
	testULP(p(0),				p(-24));
	testULP(p(0) + p(-23),		p(-23));
	testULP(p(-124),			p(-148));
	testULP(p(-125),			p(-149));
	testULP(p(-125) + p(-140),	p(-148));
	testULP(p(-126),			p(-149));
	testULP(p(-130),			p(-149));

	testRound(p(0) + p(-20) + p(-40),	p(0) + p(-20),		p(0) + p(-20) + p(-23));
	testRound(p(-126) - p(-150),		p(-126) - p(-149),	p(-126));

	TCU_CHECK(m_fmt->floatToHex(p(0)) == "0x1.000000p0");
	TCU_CHECK(m_fmt->floatToHex(p(8) + p(-4)) == "0x1.001000p8");
	TCU_CHECK(m_fmt->floatToHex(p(-140)) == "0x0.000400p-126");
	TCU_CHECK(m_fmt->floatToHex(p(-140)) == "0x0.000400p-126");
	TCU_CHECK(m_fmt->floatToHex(p(-126) + p(-125)) == "0x1.800000p-125");
}

} // anonymous

void FloatFormat_selfTest (void)
{
	TestBinary32	test32;
	test32.runTest();
}

} // tcu