small arithmetic optimization
.NET Test / .NET tests (push) Successful in 1m56s

This commit is contained in:
2026-09-20 00:52:24 +04:00
parent 34076c2466
commit 75925ab184
18 changed files with 1366 additions and 21 deletions
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using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Configs;
using Just.PreciseMath.PerformanceComparison.Reference;
namespace Just.PreciseMath.PerformanceComparison;
/// <summary>
/// Compares the four arithmetic operators on the same ordinary finite operands across
/// binary64, the <c>Just.PreciseMath</c> double-double, and the blog reference
/// implementation. Every category measures one operator, and its binary64 method is
/// the baseline, so the ratio columns read as "times the cost of a double".
/// </summary>
/// <remarks>
/// Operands are independent array elements, so the measurements include loads, stores,
/// and loop overhead on purpose; input construction, conversion, and fixture validation
/// stay outside the timed methods.
/// </remarks>
[MemoryDiagnoser]
[GroupBenchmarksBy(BenchmarkLogicalGroupRule.ByCategory)]
[CategoriesColumn]
public class ArithmeticComparisonBenchmarks
{
private double[] _doubleLeft = [];
private double[] _doubleRight = [];
private DoubleDouble[] _left = [];
private DoubleDouble[] _right = [];
private DoubleDoubleSample[] _sampleLeft = [];
private DoubleDoubleSample[] _sampleRight = [];
private readonly double[] _doubleResults = new double[PerformanceInputs.Count];
private readonly DoubleDouble[] _results = new DoubleDouble[PerformanceInputs.Count];
private readonly DoubleDoubleSample[] _sampleResults = new DoubleDoubleSample[PerformanceInputs.Count];
[GlobalSetup]
public void Setup()
{
PerformanceInputs inputs = PerformanceInputs.Create();
_doubleLeft = inputs.DoubleLeft;
_doubleRight = inputs.DoubleRight;
_left = inputs.Left;
_right = inputs.Right;
_sampleLeft = inputs.SampleLeft;
_sampleRight = inputs.SampleRight;
}
[Benchmark(Baseline = true, OperationsPerInvoke = PerformanceInputs.Count), BenchmarkCategory("Addition")]
public double[] DoubleAdd()
{
for (int i = 0; i < PerformanceInputs.Count; i++)
{
_doubleResults[i] = _doubleLeft[i] + _doubleRight[i];
}
return _doubleResults;
}
[Benchmark(OperationsPerInvoke = PerformanceInputs.Count), BenchmarkCategory("Addition")]
public DoubleDouble[] DoubleDoubleAdd()
{
for (int i = 0; i < PerformanceInputs.Count; i++)
{
_results[i] = _left[i] + _right[i];
}
return _results;
}
[Benchmark(OperationsPerInvoke = PerformanceInputs.Count), BenchmarkCategory("Addition")]
public DoubleDoubleSample[] DoubleDoubleSampleAdd()
{
for (int i = 0; i < PerformanceInputs.Count; i++)
{
_sampleResults[i] = _sampleLeft[i] + _sampleRight[i];
}
return _sampleResults;
}
[Benchmark(Baseline = true, OperationsPerInvoke = PerformanceInputs.Count), BenchmarkCategory("Subtraction")]
public double[] DoubleSubtract()
{
for (int i = 0; i < PerformanceInputs.Count; i++)
{
_doubleResults[i] = _doubleLeft[i] - _doubleRight[i];
}
return _doubleResults;
}
[Benchmark(OperationsPerInvoke = PerformanceInputs.Count), BenchmarkCategory("Subtraction")]
public DoubleDouble[] DoubleDoubleSubtract()
{
for (int i = 0; i < PerformanceInputs.Count; i++)
{
_results[i] = _left[i] - _right[i];
}
return _results;
}
[Benchmark(OperationsPerInvoke = PerformanceInputs.Count), BenchmarkCategory("Subtraction")]
public DoubleDoubleSample[] DoubleDoubleSampleSubtract()
{
for (int i = 0; i < PerformanceInputs.Count; i++)
{
_sampleResults[i] = _sampleLeft[i] - _sampleRight[i];
}
return _sampleResults;
}
[Benchmark(Baseline = true, OperationsPerInvoke = PerformanceInputs.Count), BenchmarkCategory("Multiplication")]
public double[] DoubleMultiply()
{
for (int i = 0; i < PerformanceInputs.Count; i++)
{
_doubleResults[i] = _doubleLeft[i] * _doubleRight[i];
}
return _doubleResults;
}
[Benchmark(OperationsPerInvoke = PerformanceInputs.Count), BenchmarkCategory("Multiplication")]
public DoubleDouble[] DoubleDoubleMultiply()
{
for (int i = 0; i < PerformanceInputs.Count; i++)
{
_results[i] = _left[i] * _right[i];
}
return _results;
}
[Benchmark(OperationsPerInvoke = PerformanceInputs.Count), BenchmarkCategory("Multiplication")]
public DoubleDoubleSample[] DoubleDoubleSampleMultiply()
{
for (int i = 0; i < PerformanceInputs.Count; i++)
{
_sampleResults[i] = _sampleLeft[i] * _sampleRight[i];
}
return _sampleResults;
}
[Benchmark(Baseline = true, OperationsPerInvoke = PerformanceInputs.Count), BenchmarkCategory("Division")]
public double[] DoubleDivide()
{
for (int i = 0; i < PerformanceInputs.Count; i++)
{
_doubleResults[i] = _doubleLeft[i] / _doubleRight[i];
}
return _doubleResults;
}
[Benchmark(OperationsPerInvoke = PerformanceInputs.Count), BenchmarkCategory("Division")]
public DoubleDouble[] DoubleDoubleDivide()
{
for (int i = 0; i < PerformanceInputs.Count; i++)
{
_results[i] = _left[i] / _right[i];
}
return _results;
}
[Benchmark(OperationsPerInvoke = PerformanceInputs.Count), BenchmarkCategory("Division")]
public DoubleDoubleSample[] DoubleDoubleSampleDivide()
{
for (int i = 0; i < PerformanceInputs.Count; i++)
{
_sampleResults[i] = _sampleLeft[i] / _sampleRight[i];
}
return _sampleResults;
}
}
@@ -0,0 +1,10 @@
<Project Sdk="Microsoft.NET.Sdk">
<PropertyGroup>
<OutputType>Exe</OutputType>
<TargetFramework>net10.0</TargetFramework>
<ImplicitUsings>enable</ImplicitUsings>
<Nullable>enable</Nullable>
</PropertyGroup>
</Project>
@@ -0,0 +1,135 @@
using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Configs;
using Just.PreciseMath.PerformanceComparison.Reference;
namespace Just.PreciseMath.PerformanceComparison;
/// <summary>
/// Compares Square, Sqrt, and Abs on the same ordinary finite operands across binary64,
/// the <c>Just.PreciseMath</c> double-double, and the blog reference implementation.
/// Every category measures one function, and its binary64 method is the baseline, so
/// the ratio columns read as "times the cost of a double".
/// </summary>
/// <remarks>
/// Operands are independent array elements, so the measurements include loads, stores,
/// and loop overhead on purpose; input construction and fixture validation stay outside
/// the timed methods.
/// </remarks>
[MemoryDiagnoser]
[GroupBenchmarksBy(BenchmarkLogicalGroupRule.ByCategory)]
[CategoriesColumn]
public class MathComparisonBenchmarks
{
private double[] _doublePositive = [];
private DoubleDouble[] _positive = [];
private DoubleDoubleSample[] _samplePositive = [];
private double[] _doubleMixed = [];
private DoubleDouble[] _mixed = [];
private DoubleDoubleSample[] _sampleMixed = [];
private readonly double[] _doubleResults = new double[PerformanceInputs.Count];
private readonly DoubleDouble[] _results = new DoubleDouble[PerformanceInputs.Count];
private readonly DoubleDoubleSample[] _sampleResults = new DoubleDoubleSample[PerformanceInputs.Count];
[GlobalSetup]
public void Setup()
{
PerformanceInputs inputs = PerformanceInputs.Create();
_doublePositive = inputs.DoublePositive;
_positive = inputs.Positive;
_samplePositive = inputs.SamplePositive;
// Square and Sqrt need positive operands; Abs also covers negative ones.
_doubleMixed = inputs.DoubleLeft;
_mixed = inputs.Left;
_sampleMixed = inputs.SampleLeft;
}
[Benchmark(Baseline = true, OperationsPerInvoke = PerformanceInputs.Count), BenchmarkCategory("Square")]
public double[] DoubleSquare()
{
for (int i = 0; i < PerformanceInputs.Count; i++)
{
_doubleResults[i] = _doublePositive[i] * _doublePositive[i];
}
return _doubleResults;
}
[Benchmark(OperationsPerInvoke = PerformanceInputs.Count), BenchmarkCategory("Square")]
public DoubleDouble[] DoubleDoubleSquare()
{
for (int i = 0; i < PerformanceInputs.Count; i++)
{
_results[i] = DoubleDouble.Square(_positive[i]);
}
return _results;
}
[Benchmark(OperationsPerInvoke = PerformanceInputs.Count), BenchmarkCategory("Square")]
public DoubleDoubleSample[] DoubleDoubleSampleSquare()
{
for (int i = 0; i < PerformanceInputs.Count; i++)
{
_sampleResults[i] = _samplePositive[i].Square();
}
return _sampleResults;
}
[Benchmark(Baseline = true, OperationsPerInvoke = PerformanceInputs.Count), BenchmarkCategory("Sqrt")]
public double[] DoubleSqrt()
{
for (int i = 0; i < PerformanceInputs.Count; i++)
{
_doubleResults[i] = Math.Sqrt(_doublePositive[i]);
}
return _doubleResults;
}
[Benchmark(OperationsPerInvoke = PerformanceInputs.Count), BenchmarkCategory("Sqrt")]
public DoubleDouble[] DoubleDoubleSqrt()
{
for (int i = 0; i < PerformanceInputs.Count; i++)
{
_results[i] = DoubleDouble.Sqrt(_positive[i]);
}
return _results;
}
[Benchmark(OperationsPerInvoke = PerformanceInputs.Count), BenchmarkCategory("Sqrt")]
public DoubleDoubleSample[] DoubleDoubleSampleSqrt()
{
for (int i = 0; i < PerformanceInputs.Count; i++)
{
_sampleResults[i] = _samplePositive[i].Sqrt();
}
return _sampleResults;
}
[Benchmark(Baseline = true, OperationsPerInvoke = PerformanceInputs.Count), BenchmarkCategory("Abs")]
public double[] DoubleAbs()
{
for (int i = 0; i < PerformanceInputs.Count; i++)
{
_doubleResults[i] = Math.Abs(_doubleMixed[i]);
}
return _doubleResults;
}
[Benchmark(OperationsPerInvoke = PerformanceInputs.Count), BenchmarkCategory("Abs")]
public DoubleDouble[] DoubleDoubleAbs()
{
for (int i = 0; i < PerformanceInputs.Count; i++)
{
_results[i] = DoubleDouble.Abs(_mixed[i]);
}
return _results;
}
[Benchmark(OperationsPerInvoke = PerformanceInputs.Count), BenchmarkCategory("Abs")]
public DoubleDoubleSample[] DoubleDoubleSampleAbs()
{
for (int i = 0; i < PerformanceInputs.Count; i++)
{
_sampleResults[i] = _sampleMixed[i].Abs();
}
return _sampleResults;
}
}
@@ -0,0 +1,167 @@
using Just.PreciseMath.PerformanceComparison.Reference;
namespace Just.PreciseMath.PerformanceComparison;
/// <summary>
/// Deterministic operand sets for the implementation comparison: <see cref="Count"/>
/// values per operation, each with a nonzero high and low component, built from exact
/// dyadic multiples and held inside a moderate exponent range so that no benchmark
/// path takes an overflow, underflow, or boundary branch.
/// </summary>
/// <remarks>
/// Both double-double implementations receive bit-identical operands, and the plain
/// doubles equal the high components, so the binary64 reference measures the leading
/// component of the same values. The mixed-sign set feeds +, -, *, / and Abs; the
/// nonnegative set feeds Square and Sqrt.
/// </remarks>
internal sealed class PerformanceInputs
{
/// <summary>Operands per benchmark invocation. One double-double operation takes only
/// a few nanoseconds, so an invocation covers many values and the measurement is
/// normalized back to a single operation.</summary>
internal const int Count = 200;
/// <summary>Mixed-sign operands for +, -, *, / and Abs.</summary>
internal DoubleDouble[] Left { get; } = new DoubleDouble[Count];
internal DoubleDouble[] Right { get; } = new DoubleDouble[Count];
/// <summary>Nonnegative operands for Square and Sqrt, with both components positive.</summary>
internal DoubleDouble[] Positive { get; } = new DoubleDouble[Count];
/// <summary>The same operands for the blog reference implementation.</summary>
internal DoubleDoubleSample[] SampleLeft { get; } = new DoubleDoubleSample[Count];
internal DoubleDoubleSample[] SampleRight { get; } = new DoubleDoubleSample[Count];
internal DoubleDoubleSample[] SamplePositive { get; } = new DoubleDoubleSample[Count];
/// <summary>The high components as plain doubles, for the binary64 reference.</summary>
internal double[] DoubleLeft { get; } = new double[Count];
internal double[] DoubleRight { get; } = new double[Count];
internal double[] DoublePositive { get; } = new double[Count];
internal static PerformanceInputs Create()
{
PerformanceInputs inputs = new PerformanceInputs();
for (int i = 0; i < Count; i++)
{
// Highs are small dyadic multiples of a power of two: exact in binary64,
// with the significand needing at most nine bits. Lows are multiples of
// 2^(exponent-57) or 2^(exponent-60), at least two bits below half an ulp
// of their high, so every pair is normalized and both components survive
// every operation. The exponents keep highs within 2^+-48, which leaves
// products, quotients, and squares far from the binary64 exponent limits.
int leftExponent = (((i / 4) % 5) - 2) * 24;
int rightExponent = (((i / 4) % 3) - 1) * 16;
int positiveExponent = ((i % 5) - 2) * 24;
double leftSign = (i % 2 == 0) ? 1.0 : -1.0;
double rightSign = (i % 3 == 0) ? 1.0 : -1.0;
double leftHigh = leftSign * Math.ScaleB(1.25 + ((i % 7) / 32.0), leftExponent);
double leftLow = leftSign * Math.ScaleB(1.0 + (i % 4), leftExponent - 57);
double rightHigh = rightSign * Math.ScaleB(1.0 + (((i % 5) - 2) / 128.0), rightExponent);
// Opposite sign, and a three-bit finer scale than the left low: no
// addition or multiplication of the two lows can cancel to a value that
// binary64 would represent without a residual.
double rightLow = -rightSign * Math.ScaleB(1.0 + ((i / 2) % 3), rightExponent - 60);
double positiveHigh = Math.ScaleB(1.25 + ((i % 7) / 32.0), positiveExponent);
double positiveLow = Math.ScaleB(1.0 + (i % 4), positiveExponent - 57);
inputs.Left[i] = DoubleDouble.FromComponents(leftHigh, leftLow);
inputs.Right[i] = DoubleDouble.FromComponents(rightHigh, rightLow);
inputs.Positive[i] = DoubleDouble.FromComponents(positiveHigh, positiveLow);
inputs.SampleLeft[i] = DoubleDoubleSample.FromTwoDoubles(leftHigh, leftLow);
inputs.SampleRight[i] = DoubleDoubleSample.FromTwoDoubles(rightHigh, rightLow);
inputs.SamplePositive[i] = DoubleDoubleSample.FromTwoDoubles(positiveHigh, positiveLow);
inputs.DoubleLeft[i] = leftHigh;
inputs.DoubleRight[i] = rightHigh;
inputs.DoublePositive[i] = positiveHigh;
}
inputs.Validate();
return inputs;
}
/// <summary>
/// Setup-only fixture guard. It checks the operand shape and that every benchmarked
/// operation consumes both components; it is not an accuracy oracle and does not
/// compare the two implementations against each other.
/// </summary>
private void Validate()
{
for (int i = 0; i < Count; i++)
{
ValidateOperand(Left[i], nameof(Left), i);
ValidateOperand(Right[i], nameof(Right), i);
ValidateOperand(Positive[i], nameof(Positive), i);
ValidateMatch(Left[i], SampleLeft[i], nameof(Left), i);
ValidateMatch(Right[i], SampleRight[i], nameof(Right), i);
ValidateMatch(Positive[i], SamplePositive[i], nameof(Positive), i);
if (DoubleLeft[i] != Left[i].High || DoubleRight[i] != Right[i].High || DoublePositive[i] != Positive[i].High)
{
throw new InvalidOperationException($"[{i}] the binary64 operands do not match the leading components.");
}
if (!(Positive[i].High > 0.0) || !(Positive[i].Low > 0.0))
{
throw new InvalidOperationException($"[{i}] Square and Sqrt operands must be positive in both components.");
}
}
for (int i = 0; i < Count; i++)
{
CheckResidual("Left + Right", Left[i] + Right[i], i);
CheckResidual("Left - Right", Left[i] - Right[i], i);
CheckResidual("Left * Right", Left[i] * Right[i], i);
CheckResidual("Left / Right", Left[i] / Right[i], i);
CheckResidual("Positive * Positive", DoubleDouble.Square(Positive[i]), i);
CheckResidual("Sqrt(Positive)", DoubleDouble.Sqrt(Positive[i]), i);
CheckResidual("Abs(Left)", DoubleDouble.Abs(Left[i]), i);
CheckResidual("SampleLeft + SampleRight", SampleLeft[i] + SampleRight[i], i);
CheckResidual("SampleLeft - SampleRight", SampleLeft[i] - SampleRight[i], i);
CheckResidual("SampleLeft * SampleRight", SampleLeft[i] * SampleRight[i], i);
CheckResidual("SampleLeft / SampleRight", SampleLeft[i] / SampleRight[i], i);
CheckResidual("SamplePositive.Square()", SamplePositive[i].Square(), i);
CheckResidual("SamplePositive.Sqrt()", SamplePositive[i].Sqrt(), i);
CheckResidual("SampleLeft.Abs()", SampleLeft[i].Abs(), i);
}
}
private static void ValidateOperand(DoubleDouble value, string name, int index)
{
// FromComponents renormalizes an arbitrary pair, so reproducing the value
// bit-for-bit is the normalization check for a purely dyadic construction.
bool normalized = DoubleDouble.FromComponents(value.High, value.Low).Equals(value);
if (!DoubleDouble.IsFinite(value) || value.High == 0.0 || value.Low == 0.0 || !normalized
|| Math.Abs(Math.ILogB(value.High)) > 100)
{
throw new InvalidOperationException($"{name}[{index}] is not an ordinary normalized value with both components used.");
}
}
private static void ValidateMatch(DoubleDouble value, DoubleDoubleSample sample, string name, int index)
{
bool normalized = DoubleDoubleSample.FromTwoDoubles(sample.Hi, sample.Lo).Equals(sample);
if (sample.Hi != value.High || sample.Lo != value.Low || !normalized)
{
throw new InvalidOperationException($"{name}[{index}] differs between the two double-double implementations.");
}
}
private static void CheckResidual(string operation, DoubleDouble result, int index)
{
if (!DoubleDouble.IsFinite(result) || result.Low == 0.0)
{
throw new InvalidOperationException($"{operation}[{index}] left the ordinary range or lost its low component.");
}
}
private static void CheckResidual(string operation, DoubleDoubleSample result, int index)
{
if (!double.IsFinite(result.Hi) || result.Lo == 0.0)
{
throw new InvalidOperationException($"{operation}[{index}] left the ordinary range or lost its low component.");
}
}
}
@@ -0,0 +1,23 @@
using BenchmarkDotNet.Reports;
using BenchmarkDotNet.Running;
BenchmarkSwitcher switcher = BenchmarkSwitcher.FromAssembly(typeof(Program).Assembly);
// Only these standalone discovery/help forms intentionally produce no reports.
if (args is ["--list", "flat" or "tree"] or ["--help"] or ["-h"])
{
switcher.Run(args);
return 0;
}
Summary[] summaries = [.. switcher.Run(args.Length == 0 ? ["--filter", "*"] : args)];
// BenchmarkDotNet can return normally after validation, build, or execution
// failures. Do not let CI mistake an empty or failed run for a passing smoke test.
if (summaries.Length == 0 || summaries.Any(summary =>
summary.HasCriticalValidationErrors || summary.Reports.Length == 0 ||
summary.Reports.Any(report => !report.Success || report.ResultStatistics is null)))
{
Console.Error.WriteLine("Benchmark run failed or produced no measurements.");
return 1;
}
return 0;
@@ -0,0 +1,278 @@
// Printing and parsing of DoubleDoubleSample, by Marek Fiser.
// Source: https://marekfiser.com/blog/double-double-arithmetic
// Licensed under CC BY 4.0: https://creativecommons.org/licenses/by/4.0/
// Changes for this benchmark: copied into this project, kept in the
// Just.PreciseMath.PerformanceComparison.Reference namespace, and the file and type
// renamed to DoubleDoubleSample.Format.cs and DoubleDoubleSample.
// Printing 31 correct decimal digits requires computing them exactly, which is done with
// BigInteger (part of the BCL, so still no NuGet dependencies).
using System.Globalization;
using System.Numerics;
using System.Text;
namespace Just.PreciseMath.PerformanceComparison.Reference;
public readonly partial struct DoubleDoubleSample {
/// <summary>Significant digits <see cref="ToString()"/> prints: enough to round-trip any
/// value whose two components are contiguous (see <see cref="Parse"/>).</summary>
private const int DEFAULT_DIGITS = 36;
/// <summary>Formats with <see cref="DEFAULT_DIGITS"/> significant digits.</summary>
public override string ToString() {
return ToString(DEFAULT_DIGITS);
}
/// <summary>Formats with the given number of significant decimal digits, correctly rounded.</summary>
public string ToString(int significantDigits) {
ArgumentOutOfRangeException.ThrowIfLessThan(significantDigits, 1);
if (!double.IsFinite(m_hi)) {
return m_hi.ToString(CultureInfo.InvariantCulture);
}
(BigInteger numerator, BigInteger denominator) = toRational(this);
return formatRational(numerator, denominator, significantDigits);
}
/// <summary>
/// Formats the exact value. A double-double is a sum of two binary fractions, so it
/// always has a finite decimal expansion, but it can be hundreds of digits long when the
/// components are far apart.
/// </summary>
public string ToStringExact() {
if (!double.IsFinite(m_hi)) {
return m_hi.ToString(CultureInfo.InvariantCulture);
}
(BigInteger numerator, BigInteger denominator) = toRational(this);
if (numerator.IsZero) {
return "0";
}
// The denominator is a power of two, so multiplying by the matching power of five
// turns it into a power of ten, which gives the decimal digits directly.
int twos = (int)(denominator.GetBitLength() - 1);
BigInteger scaled = BigInteger.Abs(numerator) * BigInteger.Pow(5, twos);
string digits = scaled.ToString(CultureInfo.InvariantCulture).PadLeft(twos + 1, '0');
string sign = numerator.Sign < 0 ? "-" : "";
if (twos == 0) {
return sign + digits;
}
string result = sign + digits[..^twos] + "." + digits[^twos..];
return result.TrimEnd('0').TrimEnd('.');
}
/// <summary>
/// Parses a decimal string to the nearest double-double. The value is built exactly as a
/// rational, then rounded once into each component. Round-trips with
/// <see cref="ToString()"/> for every value whose components are contiguous;
/// a hand-built pair such as (1.0, 1e-300) holds more information than 36 digits can
/// represent.
/// </summary>
public static DoubleDoubleSample Parse(string text) {
(BigInteger numerator, BigInteger denominator) = parseRational(text);
double hi = toNearestDouble(numerator, denominator);
if (!double.IsFinite(hi)) {
return FromDouble(hi);
}
// Subtract the leading component exactly and round the remainder into the trailing one.
(BigInteger hiNumerator, BigInteger hiDenominator) = toRational(FromDouble(hi));
BigInteger restNumerator = numerator * hiDenominator - hiNumerator * denominator;
BigInteger restDenominator = denominator * hiDenominator;
double lo = toNearestDouble(restNumerator, restDenominator);
return FromTwoDoubles(hi, lo);
}
/// <summary>The exact value of a double-double as a rational (the denominator is a power of two).</summary>
private static (BigInteger Numerator, BigInteger Denominator) toRational(DoubleDoubleSample value) {
(BigInteger hiNumerator, BigInteger hiDenominator) = toRational(value.m_hi);
(BigInteger loNumerator, BigInteger loDenominator) = toRational(value.m_lo);
return (hiNumerator * loDenominator + loNumerator * hiDenominator, hiDenominator * loDenominator);
}
/// <summary>The exact value of a finite double as a rational, from its bits.</summary>
private static (BigInteger Numerator, BigInteger Denominator) toRational(double value) {
long bits = BitConverter.DoubleToInt64Bits(value);
int exponent = (int)((bits >> 52) & 0x7FF);
long mantissa = bits & 0xF_FFFF_FFFF_FFFFL;
if (exponent == 0) {
exponent = -1074; // subnormal: no implicit leading bit
} else {
mantissa |= 1L << 52;
exponent -= 1075;
}
BigInteger numerator = bits < 0 ? -mantissa : mantissa;
return exponent >= 0
? (numerator << exponent, BigInteger.One)
: (numerator, BigInteger.One << -exponent);
}
/// <summary>Rounds an exact rational to the nearest double, ties to even.</summary>
private static double toNearestDouble(BigInteger numerator, BigInteger denominator) {
if (numerator.IsZero) {
return 0.0;
}
int sign = numerator.Sign;
numerator = BigInteger.Abs(numerator);
// Scale so that the quotient is in [2^52, 2^54). One integer division then gives all
// bits of the significand plus the remainder needed for the rounding.
long exponent = numerator.GetBitLength() - denominator.GetBitLength() - 53;
if (exponent > 0) {
denominator <<= (int)exponent;
} else {
numerator <<= (int)-exponent;
}
BigInteger quotient = BigInteger.DivRem(numerator, denominator, out BigInteger remainder);
if (quotient.GetBitLength() > 53) {
// One bit too many. Move it to the exponent and add the dropped bit to the
// remainder so that the rounding decision below stays exact.
if (!quotient.IsEven) {
remainder += denominator;
}
quotient >>= 1;
denominator <<= 1;
exponent++;
}
int comparison = (remainder << 1).CompareTo(denominator);
if (comparison > 0 || (comparison == 0 && !quotient.IsEven)) {
quotient++;
if (quotient.GetBitLength() > 53) {
quotient >>= 1;
exponent++;
}
}
return sign * Math.ScaleB((double)quotient, (int)exponent);
}
/// <summary>Parses a decimal string such as "-1.25e-7" into an exact rational.</summary>
private static (BigInteger Numerator, BigInteger Denominator) parseRational(string text) {
text = text.Trim();
if (text.Length == 0) {
throw new FormatException("Empty input.");
}
int index = 0;
bool negative = text[index] == '-';
if (negative || text[index] == '+') {
index++;
}
BigInteger mantissa = BigInteger.Zero;
int fractionDigits = 0;
bool seenDot = false;
bool seenDigit = false;
for (; index < text.Length; index++) {
char c = text[index];
if (c == '.') {
if (seenDot) {
throw new FormatException($"Two decimal points in '{text}'.");
}
seenDot = true;
} else if (c is >= '0' and <= '9') {
mantissa = mantissa * 10 + (c - '0');
seenDigit = true;
if (seenDot) {
fractionDigits++;
}
} else if (c is 'e' or 'E') {
break;
} else {
throw new FormatException($"Unexpected character '{c}' in '{text}'.");
}
}
if (!seenDigit) {
throw new FormatException($"No digits in '{text}'.");
}
int exponent = -fractionDigits;
if (index < text.Length) {
exponent += int.Parse(text[(index + 1)..], CultureInfo.InvariantCulture);
}
if (negative) {
mantissa = -mantissa;
}
return exponent >= 0
? (mantissa * BigInteger.Pow(10, exponent), BigInteger.One)
: (mantissa, BigInteger.Pow(10, -exponent));
}
/// <summary>Rounds an exact rational to N significant digits and formats them.</summary>
private static string formatRational(BigInteger numerator, BigInteger denominator, int digits) {
if (numerator.IsZero) {
return "0";
}
bool negative = numerator.Sign < 0;
numerator = BigInteger.Abs(numerator);
// Estimate of the decimal exponent of the leading digit from the bit lengths
// (log10(2) ~ 0.30103). The loop below corrects it when the estimate is off by one.
int exponent10 = (int)Math.Floor((numerator.GetBitLength() - denominator.GetBitLength()) * 0.30103);
string text;
while (true) {
int scale = digits - 1 - exponent10;
BigInteger scaledNumerator = numerator;
BigInteger scaledDenominator = denominator;
if (scale >= 0) {
scaledNumerator *= BigInteger.Pow(10, scale);
} else {
scaledDenominator *= BigInteger.Pow(10, -scale);
}
BigInteger rounded = roundToNearest(scaledNumerator, scaledDenominator);
text = rounded.ToString(CultureInfo.InvariantCulture);
if (text.Length == digits) {
break;
}
// Off by one either way (estimate too low, or rounding carried into a new digit).
exponent10 += text.Length - digits;
}
text = text.TrimEnd('0');
if (text.Length == 0) {
text = "0";
}
StringBuilder result = new(negative ? "-" : "");
if (exponent10 >= -5 && exponent10 < digits) {
// Positional notation for the range where it is readable.
if (exponent10 >= 0) {
text = text.PadRight(exponent10 + 1, '0');
result.Append(text[..(exponent10 + 1)]);
if (text.Length > exponent10 + 1) {
result.Append('.').Append(text[(exponent10 + 1)..]);
}
} else {
result.Append("0.").Append('0', -exponent10 - 1).Append(text);
}
} else {
result.Append(text[0]);
if (text.Length > 1) {
result.Append('.').Append(text[1..]);
}
result.Append('e').Append(exponent10.ToString(CultureInfo.InvariantCulture));
}
return result.ToString();
}
/// <summary>Integer nearest to numerator/denominator, ties away from zero (both positive).</summary>
private static BigInteger roundToNearest(BigInteger numerator, BigInteger denominator) {
BigInteger quotient = BigInteger.DivRem(numerator, denominator, out BigInteger remainder);
return (remainder << 1) >= denominator ? quotient + 1 : quotient;
}
}
@@ -0,0 +1,213 @@
// Double-double arithmetic in about 200 lines, by Marek Fiser.
// Source: https://marekfiser.com/blog/double-double-arithmetic
// Licensed under CC BY 4.0: https://creativecommons.org/licenses/by/4.0/
// Changes for this benchmark: copied into this project, kept in the
// Just.PreciseMath.PerformanceComparison.Reference namespace, and the file and type
// renamed to DoubleDoubleSample.
// This file depends only on System so that it can be copied into any project. Printing and
// parsing use BigInteger and are in DoubleDoubleSample.Format.cs.
namespace Just.PreciseMath.PerformanceComparison.Reference;
/// <summary>
/// A value stored as the unevaluated sum of two doubles: ~106 significand bits
/// (~31 decimal digits) at a few times the cost of a double, with no heap allocation.
///
/// Invariant: Hi == RoundToNearest(Hi + Lo), i.e. |Lo| is at most half an ulp of Hi.
/// Every factory and operation below maintains it; comparisons and ToDouble rely on it.
///
/// Operations are not correctly rounded but stay within a few units of 2^-106 of the
/// exact result. The exponent range is the same as a plain double's, and infinities are
/// not special-cased: the first operation on one returns NaN (the error terms compute
/// inf - inf).
///
/// By Marek Fiser, from marekfiser.com/blog/double-double-arithmetic/ (CC BY 4.0; the file
/// header carries the full attribution and license notice).
/// </summary>
public readonly partial struct DoubleDoubleSample : IEquatable<DoubleDoubleSample>, IComparable<DoubleDoubleSample> {
private readonly double m_hi;
private readonly double m_lo;
/// <summary>The leading component; equals the value rounded to nearest double.</summary>
public double Hi => m_hi;
/// <summary>The trailing component (the rounding error of <see cref="Hi"/>).</summary>
public double Lo => m_lo;
public bool IsZero => m_hi == 0.0;
/// <summary>-1, 0 or +1 (0 also for NaN).</summary>
public int Sign => m_hi > 0.0 ? 1 : m_hi < 0.0 ? -1 : 0;
public static DoubleDoubleSample Zero { get; } = new DoubleDoubleSample(0.0, 0.0);
public static DoubleDoubleSample One { get; } = new DoubleDoubleSample(1.0, 0.0);
private DoubleDoubleSample(double hi, double lo) {
m_hi = hi;
m_lo = lo;
}
/// <summary>Exact conversion from a double.</summary>
public static DoubleDoubleSample FromDouble(double value) {
return new DoubleDoubleSample(value, 0.0);
}
/// <summary>The exact sum <paramref name="hi"/> + <paramref name="lo"/> of two arbitrary doubles.</summary>
public static DoubleDoubleSample FromTwoDoubles(double hi, double lo) {
// Renormalizes so that the invariant holds.
(double sum, double error) = twoSum(hi, lo);
return new DoubleDoubleSample(sum, error);
}
public DoubleDoubleSample Add(DoubleDoubleSample right) {
// Add the two components pairwise, then incorporate lowSum and lowError one by one.
// Adding lowError can round, so a second quickTwoSum renormalizes the result.
(double sum, double error) = twoSum(m_hi, right.m_hi);
(double lowSum, double lowError) = twoSum(m_lo, right.m_lo);
error += lowSum;
(sum, error) = quickTwoSum(sum, error);
error += lowError;
(sum, error) = quickTwoSum(sum, error);
return new DoubleDoubleSample(sum, error);
}
public DoubleDoubleSample Subtract(DoubleDoubleSample right) {
return Add(right.Negate());
}
public DoubleDoubleSample Multiply(DoubleDoubleSample right) {
// hi*hi exactly, then the three cross terms. Each cross term is at least 2^-53 smaller
// than the product, so plain double arithmetic is accurate enough for them.
(double product, double error) = twoProduct(m_hi, right.m_hi);
error += m_hi * right.m_lo + m_lo * right.m_hi + m_lo * right.m_lo;
(product, error) = quickTwoSum(product, error);
return new DoubleDoubleSample(product, error);
}
/// <summary>Multiplies by a plain double. Faster than the full double-double product.</summary>
public DoubleDoubleSample Multiply(double right) {
(double product, double error) = twoProduct(m_hi, right);
error += m_lo * right;
(product, error) = quickTwoSum(product, error);
return new DoubleDoubleSample(product, error);
}
/// <summary>Slower and slightly less accurate than the other operations.</summary>
public DoubleDoubleSample Divide(DoubleDoubleSample right) {
// Three steps of long division.
double quotient1 = m_hi / right.m_hi;
DoubleDoubleSample remainder = Subtract(right.Multiply(quotient1));
double quotient2 = remainder.m_hi / right.m_hi;
remainder = remainder.Subtract(right.Multiply(quotient2));
double quotient3 = remainder.m_hi / right.m_hi;
(double sum, double error) = quickTwoSum(quotient1, quotient2);
return new DoubleDoubleSample(sum, error).Add(FromDouble(quotient3));
}
/// <summary>Slightly faster than the general product.</summary>
public DoubleDoubleSample Square() {
(double product, double error) = twoProduct(m_hi, m_hi);
error += 2.0 * m_hi * m_lo + m_lo * m_lo;
(product, error) = quickTwoSum(product, error);
return new DoubleDoubleSample(product, error);
}
public DoubleDoubleSample Negate() {
// Negation never rounds, so this is exact.
return new DoubleDoubleSample(-m_hi, -m_lo);
}
public DoubleDoubleSample Abs() {
return Sign < 0 ? Negate() : this;
}
/// <summary>Slightly less accurate than the other operations. Negative and NaN inputs
/// return NaN, as Math.Sqrt does.</summary>
public DoubleDoubleSample Sqrt() {
if (!(m_hi > 0.0)) { // Not "m_hi <= 0.0", because this form is also true for NaN.
return FromDouble(Math.Sqrt(m_hi));
}
// One Newton step from the double square root.
double approx = Math.Sqrt(m_hi);
DoubleDoubleSample residual = Subtract(FromDouble(approx).Square());
double correction = residual.m_hi / (approx + approx);
(double hi, double lo) = quickTwoSum(approx, correction);
return new DoubleDoubleSample(hi, lo);
}
public double ToDouble() {
return m_hi;
}
public int CompareTo(DoubleDoubleSample other) {
// Correct only for normalized pairs.
int hiComparison = m_hi.CompareTo(other.m_hi);
return hiComparison != 0 ? hiComparison : m_lo.CompareTo(other.m_lo);
}
public bool Equals(DoubleDoubleSample other) {
return m_hi == other.m_hi && m_lo == other.m_lo;
}
public override bool Equals(object? obj) {
return obj is DoubleDoubleSample other && Equals(other);
}
public override int GetHashCode() {
return HashCode.Combine(m_hi, m_lo);
}
public static DoubleDoubleSample operator +(DoubleDoubleSample left, DoubleDoubleSample right) => left.Add(right);
public static DoubleDoubleSample operator -(DoubleDoubleSample left, DoubleDoubleSample right) => left.Subtract(right);
public static DoubleDoubleSample operator *(DoubleDoubleSample left, DoubleDoubleSample right) => left.Multiply(right);
public static DoubleDoubleSample operator *(DoubleDoubleSample left, double right) => left.Multiply(right);
public static DoubleDoubleSample operator /(DoubleDoubleSample left, DoubleDoubleSample right) => left.Divide(right);
public static DoubleDoubleSample operator -(DoubleDoubleSample value) => value.Negate();
public static bool operator ==(DoubleDoubleSample left, DoubleDoubleSample right) => left.Equals(right);
public static bool operator !=(DoubleDoubleSample left, DoubleDoubleSample right) => !left.Equals(right);
public static bool operator <(DoubleDoubleSample left, DoubleDoubleSample right) => left.CompareTo(right) < 0;
public static bool operator >(DoubleDoubleSample left, DoubleDoubleSample right) => left.CompareTo(right) > 0;
public static bool operator <=(DoubleDoubleSample left, DoubleDoubleSample right) => left.CompareTo(right) <= 0;
public static bool operator >=(DoubleDoubleSample left, DoubleDoubleSample right) => left.CompareTo(right) >= 0;
// Conversion from a double is exact, so it is implicit. Conversion to a double drops the
// low component, so it is explicit.
public static implicit operator DoubleDoubleSample(double value) => FromDouble(value);
public static explicit operator double(DoubleDoubleSample value) => value.ToDouble();
/// <summary>Knuth's two-sum: sum + error == a + b exactly, for any two doubles.</summary>
private static (double Sum, double Error) twoSum(double a, double b) {
// The rounding error of a floating-point addition is itself representable as a double.
// The intermediate results below may round, but their rounding errors cancel out.
double sum = a + b;
double bKept = sum - a; // The part of b that made it into the sum.
double aKept = sum - bKept; // The part of a that made it into the sum.
double aLost = a - aKept;
double bLost = b - bKept;
return (sum, aLost + bLost);
}
/// <summary>Dekker's fast two-sum: the same guarantee as twoSum, valid only when
/// |a| >= |b| (or a == 0).</summary>
private static (double Sum, double Error) quickTwoSum(double a, double b) {
double sum = a + b;
double bKept = sum - a;
return (sum, b - bKept); // a lost nothing, so only b's loss remains.
}
/// <summary>Exact product: product + error == a * b exactly, as long as the product is a
/// normal double. Below about 2e-292 the error no longer fits a double.</summary>
private static (double Product, double Error) twoProduct(double a, double b) {
// The fused multiply-add computes a*b - product with a single rounding, which is the
// low half of the 106-bit product. On a CPU without an FMA instruction,
// Math.FusedMultiplyAdd computes the same result in software, much slower.
double product = a * b;
double error = Math.FusedMultiplyAdd(a, b, -product);
return (product, error);
}
}
@@ -0,0 +1,174 @@
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