731 lines
24 KiB
C#
731 lines
24 KiB
C#
using System;
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using System.Buffers.Binary;
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using BenchmarkDotNet.Attributes;
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using BenchmarkDotNet.Jobs;
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using System.Numerics;
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using PerfectNumbers.Core;
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namespace EvenPerfectBitScanner.Benchmarks;
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/// <remarks>
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/// Benchmark results collected on AMD Ryzen 5 5625U (.NET 8.0, launchCount: 1, warmupCount: 1, iterationCount: 5):
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/// Small sample (~1e6 random odd moduli)
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/// - MontgomeryWithoutCycle: 35.41 µs (baseline)
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/// - MontgomeryWithPrecomputedCycle: 25.81 µs (0.73× baseline)
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/// - MontgomeryWithGpuCycleComputation: 54.09 ms (1,527× baseline, includes GPU cycle calculation)
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/// Large sample (Mersenne-like moduli from 2^48-1 to 2^63-1)
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/// - MontgomeryWithoutCycle: 117.33 µs (baseline)
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/// - MontgomeryWithPrecomputedCycle: 9.12 µs (0.08× baseline)
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/// - MontgomeryWithGpuCycleComputation: 12.91 µs (0.11× baseline)
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/// </remarks>
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[MemoryDiagnoser]
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[SimpleJob(RuntimeMoniker.Net80, launchCount: 1, warmupCount: 1, iterationCount: 5)]
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public class Pow2MontgomeryModBenchmarks
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{
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private const int SampleCount = 256;
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private const ulong OneShiftedLeft63 = 1UL << 63;
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private const long OneShiftedLeft60 = 1L << 60;
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private readonly MontgomeryDivisorData[] _smallDivisors = new MontgomeryDivisorData[SampleCount];
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private readonly MontgomeryDivisorData[] _largeDivisors = new MontgomeryDivisorData[SampleCount];
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private readonly MontgomeryDivisorData[] _veryLargeDivisors = new MontgomeryDivisorData[SampleCount];
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private readonly UInt128[] _wideModuli = new UInt128[SampleCount];
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private readonly ulong[] _smallExponents = new ulong[SampleCount];
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private readonly ulong[] _largeExponents = new ulong[SampleCount];
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private readonly ulong[] _veryLargeExponents = new ulong[SampleCount];
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private readonly ulong[] _smallCycles = new ulong[SampleCount];
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private readonly ulong[] _largeCycles = new ulong[SampleCount];
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private readonly ulong[] _veryLargeCycles = new ulong[SampleCount];
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private readonly UInt128[] _wideCycles = new UInt128[SampleCount];
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private readonly Random _random = new(13);
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private readonly Random _heuristicRandom = new(113);
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private ulong? _previousPrimeOrder;
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private UInt128? _previousWidePrimeOrder;
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public enum InputScale
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{
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Small,
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Large,
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VeryLarge
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}
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[ParamsAllValues]
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public InputScale Scale { get; set; }
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[GlobalSetup]
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public void Setup()
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{
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for (int i = 0; i < SampleCount; i++)
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{
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#if DEBUG
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Console.WriteLine($"Generating sample {i}");
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#endif
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ulong smallModulus = NextSmallOddModulus();
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_smallDivisors[i] = CreateMontgomeryDivisorData(smallModulus);
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_smallExponents[i] = NextSmallExponent();
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_smallCycles[i] = MersenneDivisorCycles.CalculateCycleLength(smallModulus, MontgomeryDivisorData.FromModulus(smallModulus));
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(ulong largeModulus, ulong largeCycle) = NextLargeModulusAndCycle();
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_largeDivisors[i] = CreateMontgomeryDivisorData(largeModulus);
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_largeExponents[i] = NextLargeExponent();
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_largeCycles[i] = largeCycle;
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ulong veryLargeModulus = NextVeryLargeOddModulus();
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_veryLargeDivisors[i] = CreateMontgomeryDivisorData(veryLargeModulus);
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_veryLargeExponents[i] = NextVeryLargeExponent();
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#if DEBUG
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Console.WriteLine($"Calculating cycle length {veryLargeModulus}");
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#endif
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_veryLargeCycles[i] = CalculateCycleLengthWithHeuristics(veryLargeModulus);
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Console.WriteLine($"Generating wide sample {i}");
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UInt128 wideModulus = NextWideOddModulus();
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_wideModuli[i] = wideModulus;
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_wideCycles[i] = CalculateCycleLengthWithHeuristics(wideModulus);
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}
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}
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/// <summary>
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/// Baseline right-to-left Montgomery ladder; measured 36.36 μs on the small sample set and 117.32 μs on the large one.
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/// </summary>
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[Benchmark(Baseline = true)]
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public ulong BaselineCpu()
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{
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GetData(out var exponents, out var divisors, out _);
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ulong checksum = 0UL;
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for (int i = 0; i < SampleCount; i++)
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{
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checksum ^= exponents[i].Pow2MontgomeryModWindowedCpu(divisors[i], keepMontgomery: false);
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}
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return checksum;
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}
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/// <summary>
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/// Baseline right-to-left Montgomery ladder; measured ??.?? μs on the small sample set and ??.?? μs on the large one.
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/// </summary>
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[Benchmark]
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public ulong BaselineGpu()
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{
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GetData(out var exponents, out var divisors, out _);
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ulong checksum = 0UL;
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for (int i = 0; i < SampleCount; i++)
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{
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checksum ^= exponents[i].Pow2MontgomeryModWindowedGpu(divisors[i], keepMontgomery: false);
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}
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return checksum;
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}
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/// <summary>
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/// Uses a known divisor cycle to fold the exponent first, dropping runtimes to 26.04 μs on small inputs (0.72× baseline) and 9.53 μs on large inputs (0.08× baseline).
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/// </summary>
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[Benchmark]
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public ulong BaselineWithKnownCycleCpu()
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{
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GetData(out var exponents, out var divisors, out var cycles);
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ulong checksum = 0UL;
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for (int i = 0; i < SampleCount; i++)
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{
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checksum ^= exponents[i].Pow2MontgomeryModWithCycleCpu(cycles[i], divisors[i]);
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}
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return checksum;
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}
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/// <summary>
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/// Uses a known divisor cycle to fold the exponent first, dropping runtimes to 26.04 μs on small inputs (0.72× baseline) and 9.53 μs on large inputs (0.08× baseline).
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/// </summary>
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[Benchmark]
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public ulong BaselineWithKnownCycleGpu()
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{
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GetData(out var exponents, out var divisors, out var cycles);
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ulong checksum = 0UL;
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for (int i = 0; i < SampleCount; i++)
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{
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checksum ^= exponents[i].Pow2MontgomeryModWithCycleGpu(cycles[i], divisors[i]);
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}
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return checksum;
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}
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/// <summary>
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/// Montgomery reduction with the cycle computed on the fly using the GPU helper; costs 54.09 ms on the small benchmark due to
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/// cycle discovery, but drops to 12.91 μs on the large set (0.11× baseline).
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/// </summary>
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// [Benchmark]
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public ulong MontgomeryWithGpuCycleComputationCpu()
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{
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GetData(out var exponents, out var divisors, out _);
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ulong checksum = 0UL;
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for (int i = 0; i < SampleCount; i++)
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{
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ulong cycle = MersenneDivisorCycles.CalculateCycleLengthGpu(divisors[i].Modulus);
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checksum ^= exponents[i].Pow2MontgomeryModWithCycleCpu(cycle, divisors[i]);
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}
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return checksum;
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}
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/// <summary>
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/// Montgomery reduction with the cycle computed on the fly using the GPU helper; costs 54.09 ms on the small benchmark due to
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/// cycle discovery, but drops to 12.91 μs on the large set (0.11× baseline).
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/// </summary>
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// [Benchmark]
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public ulong MontgomeryWithGpuCycleComputationGpu()
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{
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GetData(out var exponents, out var divisors, out _);
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ulong checksum = 0UL;
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for (int i = 0; i < SampleCount; i++)
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{
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ulong cycle = MersenneDivisorCycles.CalculateCycleLengthGpu(divisors[i].Modulus);
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checksum ^= exponents[i].Pow2MontgomeryModWithCycleGpu(cycle, divisors[i]);
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}
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return checksum;
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}
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[Benchmark]
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public ulong MontgomeryWithHeuristicCycleComputationCpu()
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{
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GetData(out var exponents, out var divisors, out _);
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ulong checksum = 0UL;
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for (int i = 0; i < SampleCount; i++)
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{
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ulong cycle = CalculateCycleLengthWithHeuristics(divisors[i].Modulus);
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checksum ^= exponents[i].Pow2MontgomeryModWithCycleCpu(cycle, divisors[i]);
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}
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return checksum;
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}
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// [Benchmark]
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public ulong MontgomeryWithHeuristicCycleComputationGpu()
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{
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GetData(out var exponents, out var divisors, out _);
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ulong checksum = 0UL;
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for (int i = 0; i < SampleCount; i++)
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{
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ulong cycle = CalculateCycleLengthWithHeuristics(divisors[i].Modulus);
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checksum ^= exponents[i].Pow2MontgomeryModWithCycleGpu(cycle, divisors[i]);
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}
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return checksum;
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}
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// [Benchmark]
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public UInt128 HeuristicWideCycleComputation()
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{
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UInt128 checksum = UInt128.Zero;
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for (int i = 0; i < SampleCount; i++)
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{
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UInt128 cycle = CalculateCycleLengthWithHeuristics(_wideModuli[i]);
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_wideCycles[i] = cycle;
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checksum ^= cycle;
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}
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return checksum;
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}
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/// <summary>
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/// Left-to-right Montgomery scan that trails the baseline: 39.11 μs on small inputs (1.08×) and 126.38 μs on large ones (1.08×).
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/// </summary>
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[Benchmark]
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public ulong LeftToRight()
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{
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GetData(out var exponents, out var divisors, out _);
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ulong checksum = 0UL;
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for (int i = 0; i < SampleCount; i++)
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{
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checksum ^= Pow2MontgomeryModLeftToRight(exponents[i], divisors[i]);
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}
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return checksum;
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}
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/// <summary>
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/// Processes four exponent bits per loop, finishing at 38.74 μs on small cases (1.07× baseline) and 120.11 μs on large ones (1.02×).
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/// </summary>
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[Benchmark]
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public ulong Batched4()
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{
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GetData(out var exponents, out var divisors, out _);
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ulong checksum = 0UL;
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for (int i = 0; i < SampleCount; i++)
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{
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checksum ^= Pow2MontgomeryModBatched4(exponents[i], divisors[i]);
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}
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return checksum;
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}
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/// <summary>
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/// Windowed Montgomery ladder (width 5) that lags behind the baseline at 52.82 μs on small samples (1.45×) and 124.13 μs on large samples (1.06×).
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/// </summary>
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[Benchmark]
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public ulong SlidingWindow()
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{
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GetData(out var exponents, out var divisors, out _);
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ulong checksum = 0UL;
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for (int i = 0; i < SampleCount; i++)
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{
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checksum ^= Pow2MontgomeryModSlidingWindow(exponents[i], divisors[i]);
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}
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return checksum;
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}
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/// <summary>
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/// Classic binary ladder without Montgomery reduction; runs 24.75 μs on small inputs (0.68× baseline) but collapses to 295.29 μs on large ones (2.52×).
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/// </summary>
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[Benchmark]
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public ulong BinaryMod()
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{
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GetData(out var exponents, out var divisors, out _);
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ulong checksum = 0UL;
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for (int i = 0; i < SampleCount; i++)
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{
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checksum ^= Pow2ModBinary(exponents[i], divisors[i].Modulus);
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}
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return checksum;
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}
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/// <summary>
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/// Precomputes all squarings once; 30.18 μs on small inputs (0.83× baseline) but 289.80 μs on large ones (2.47×).
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/// </summary>
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[Benchmark]
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public ulong PrecomputedTableMod()
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{
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GetData(out var exponents, out var divisors, out _);
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ulong checksum = 0UL;
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for (int i = 0; i < SampleCount; i++)
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{
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checksum ^= Pow2ModPrecomputedTable(exponents[i], divisors[i].Modulus);
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}
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return checksum;
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}
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/// <summary>
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/// Relies on <see cref="BigInteger.ModPow"/>; fastest on small inputs at 17.21 μs (0.47× baseline) but slowest on large ones at 562.78 μs (4.80×).
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/// </summary>
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[Benchmark]
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public ulong BigIntegerMod()
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{
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GetData(out var exponents, out var divisors, out _);
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ulong checksum = 0UL;
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for (int i = 0; i < SampleCount; i++)
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{
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checksum ^= Pow2ModBigInteger(exponents[i], divisors[i].Modulus);
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}
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return checksum;
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}
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private void GetData(out ulong[] exponents, out MontgomeryDivisorData[] divisors, out ulong[] cycles)
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{
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switch (Scale)
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{
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case InputScale.Small:
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exponents = _smallExponents;
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divisors = _smallDivisors;
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cycles = _smallCycles;
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break;
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case InputScale.Large:
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exponents = _largeExponents;
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divisors = _largeDivisors;
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cycles = _largeCycles;
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break;
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case InputScale.VeryLarge:
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exponents = _veryLargeExponents;
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divisors = _veryLargeDivisors;
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cycles = _veryLargeCycles;
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break;
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default:
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throw new ArgumentOutOfRangeException(nameof(Scale), Scale, null);
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}
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}
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private ulong NextSmallExponent() => (ulong)_random.NextInt64(1L, 1_000_000L);
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private ulong NextLargeExponent() => (ulong)_random.NextInt64(OneShiftedLeft60, long.MaxValue);
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private ulong NextVeryLargeExponent()
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{
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Span<byte> buffer = stackalloc byte[8];
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_heuristicRandom.NextBytes(buffer);
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ulong value = checked(BinaryPrimitives.ReadUInt64LittleEndian(buffer) | OneShiftedLeft63);
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return value;
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}
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private ulong NextSmallOddModulus()
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{
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ulong value = (ulong)_random.NextInt64(3L, 1_000_000L);
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return value | 1UL;
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}
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private (ulong modulus, ulong cycleLength) NextLargeModulusAndCycle()
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{
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int bitLength = _random.Next(48, 64);
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ulong modulus = (1UL << bitLength) - 1UL;
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return (modulus, (ulong)bitLength);
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}
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private ulong NextVeryLargeOddModulus()
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{
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Span<byte> buffer = stackalloc byte[8];
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_heuristicRandom.NextBytes(buffer);
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ulong value = BinaryPrimitives.ReadUInt64LittleEndian(buffer) | OneShiftedLeft63 | 1UL;
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return value;
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}
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private UInt128 NextWideOddModulus()
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{
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Span<byte> buffer = stackalloc byte[16];
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_heuristicRandom.NextBytes(buffer);
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ulong low = BinaryPrimitives.ReadUInt64LittleEndian(buffer);
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Span<byte> highSlice = buffer.Slice(8, 8);
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ulong high = BinaryPrimitives.ReadUInt64LittleEndian(highSlice) | (1UL << 63);
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UInt128 value = ((UInt128)high << 64) | low;
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return value | UInt128.One;
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}
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private static MontgomeryDivisorData CreateMontgomeryDivisorData(ulong modulus)
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{
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if (modulus <= 1UL || (modulus & 1UL) == 0UL)
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{
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return new MontgomeryDivisorData(modulus, 0UL, 0UL, 0UL, 0UL);
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}
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ulong nPrime = ComputeMontgomeryNPrime(modulus);
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ulong montgomeryOne = ComputeMontgomeryResidue(1UL, modulus);
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ulong montgomeryTwo = ComputeMontgomeryResidue(2UL, modulus);
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ulong montgomeryTwoSquared = ULongExtensions.MontgomeryMultiply(montgomeryTwo, montgomeryTwo, modulus, nPrime);
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return new MontgomeryDivisorData(
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modulus,
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nPrime,
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montgomeryOne,
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montgomeryTwo,
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montgomeryTwoSquared);
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}
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private ulong CalculateCycleLengthWithHeuristics(ulong modulus, ulong fallbackOrder = 0UL)
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{
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MontgomeryDivisorData divisorData = MontgomeryDivisorData.FromModulus(modulus);
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if (modulus <= 1UL || (modulus & 1UL) == 0UL)
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{
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return fallbackOrder != 0UL ? fallbackOrder : MersenneDivisorCycles.CalculateCycleLength(modulus, divisorData);
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}
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#if DEBUG
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Console.WriteLine("Trying heuristic. Prime order calculation");
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#endif
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ulong order = PrimeOrderCalculator.Calculate(
|
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modulus,
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_previousPrimeOrder,
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divisorData,
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PrimeOrderCalculator.PrimeOrderSearchConfig.HeuristicDefault,
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PrimeOrderCalculator.PrimeOrderHeuristicDevice.Gpu);
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if (order != 0UL)
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{
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_previousPrimeOrder = order;
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return order;
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}
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_previousPrimeOrder = null;
|
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Console.WriteLine($"Heuristic failed for {modulus}, falling back to full cycle calculation");
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return fallbackOrder != 0UL ? fallbackOrder : MersenneDivisorCycles.CalculateCycleLength(modulus, divisorData);
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}
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private UInt128 CalculateCycleLengthWithHeuristics(UInt128 modulus)
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{
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if (modulus <= UInt128.One || (modulus & UInt128.One) == UInt128.Zero)
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{
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return MersenneDivisorCycles.GetCycle(modulus);
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}
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#if DEBUG
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Console.WriteLine("Trying heuristic. Wide prime order calculation");
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#endif
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UInt128 order = PrimeOrderCalculator.Calculate(
|
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modulus,
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_previousWidePrimeOrder,
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PrimeOrderCalculator.PrimeOrderSearchConfig.HeuristicDefault,
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PrimeOrderCalculator.PrimeOrderHeuristicDevice.Gpu);
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if (order != UInt128.Zero)
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{
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_previousWidePrimeOrder = order;
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return order;
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}
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_previousWidePrimeOrder = null;
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Console.WriteLine($"Wide heuristic failed for {modulus}, falling back to full cycle calculation");
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return MersenneDivisorCycles.GetCycle(modulus);
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}
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private static ulong ComputeMontgomeryResidue(ulong value, ulong modulus) => (ulong)((UInt128)value * (UInt128.One << 64) % modulus);
|
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private static ulong ComputeMontgomeryNPrime(ulong modulus)
|
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{
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ulong inv = modulus;
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inv *= unchecked(2UL - modulus * inv);
|
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inv *= unchecked(2UL - modulus * inv);
|
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inv *= unchecked(2UL - modulus * inv);
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inv *= unchecked(2UL - modulus * inv);
|
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inv *= unchecked(2UL - modulus * inv);
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inv *= unchecked(2UL - modulus * inv);
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return unchecked(0UL - inv);
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}
|
||
|
||
private static ulong Pow2MontgomeryModLeftToRight(ulong exponent, in MontgomeryDivisorData divisor)
|
||
{
|
||
ulong modulus = divisor.Modulus;
|
||
if (modulus <= 1UL || (modulus & 1UL) == 0UL)
|
||
{
|
||
return 0UL;
|
||
}
|
||
|
||
ulong result = divisor.MontgomeryOne;
|
||
ulong baseVal = divisor.MontgomeryTwo;
|
||
ulong nPrime = divisor.NPrime;
|
||
|
||
if (exponent == 0UL)
|
||
{
|
||
return result.MontgomeryMultiply(1UL, modulus, nPrime);
|
||
}
|
||
|
||
int msbIndex = 63 - BitOperations.LeadingZeroCount(exponent);
|
||
|
||
for (int bitIndex = msbIndex; bitIndex >= 0; bitIndex--)
|
||
{
|
||
result = result.MontgomeryMultiply(result, modulus, nPrime);
|
||
|
||
if (((exponent >> bitIndex) & 1UL) != 0UL)
|
||
{
|
||
result = result.MontgomeryMultiply(baseVal, modulus, nPrime);
|
||
}
|
||
}
|
||
|
||
return result.MontgomeryMultiply(1UL, modulus, nPrime);
|
||
}
|
||
|
||
private static ulong Pow2MontgomeryModBatched4(ulong exponent, in MontgomeryDivisorData divisor)
|
||
{
|
||
ulong modulus = divisor.Modulus;
|
||
if (modulus <= 1UL || (modulus & 1UL) == 0UL)
|
||
{
|
||
return 0UL;
|
||
}
|
||
|
||
ulong result = divisor.MontgomeryOne;
|
||
ulong baseVal = divisor.MontgomeryTwo;
|
||
ulong nPrime = divisor.NPrime;
|
||
ulong remainingExponent = exponent;
|
||
|
||
while (remainingExponent != 0UL)
|
||
{
|
||
ulong nibble = remainingExponent & 0xFUL;
|
||
|
||
ulong base0 = baseVal;
|
||
ulong base1 = base0.MontgomeryMultiply(base0, modulus, nPrime);
|
||
ulong base2 = base1.MontgomeryMultiply(base1, modulus, nPrime);
|
||
ulong base3 = base2.MontgomeryMultiply(base2, modulus, nPrime);
|
||
|
||
if ((nibble & 1UL) != 0UL)
|
||
{
|
||
result = result.MontgomeryMultiply(base0, modulus, nPrime);
|
||
}
|
||
|
||
if ((nibble & 2UL) != 0UL)
|
||
{
|
||
result = result.MontgomeryMultiply(base1, modulus, nPrime);
|
||
}
|
||
|
||
if ((nibble & 4UL) != 0UL)
|
||
{
|
||
result = result.MontgomeryMultiply(base2, modulus, nPrime);
|
||
}
|
||
|
||
if ((nibble & 8UL) != 0UL)
|
||
{
|
||
result = result.MontgomeryMultiply(base3, modulus, nPrime);
|
||
}
|
||
|
||
baseVal = base3.MontgomeryMultiply(base3, modulus, nPrime);
|
||
remainingExponent >>= 4;
|
||
}
|
||
|
||
return result.MontgomeryMultiply(1UL, modulus, nPrime);
|
||
}
|
||
|
||
private static ulong Pow2MontgomeryModSlidingWindow(ulong exponent, in MontgomeryDivisorData divisor)
|
||
{
|
||
ulong modulus = divisor.Modulus;
|
||
if (modulus <= 1UL || (modulus & 1UL) == 0UL)
|
||
{
|
||
return 0UL;
|
||
}
|
||
|
||
ulong nPrime = divisor.NPrime;
|
||
ulong result = divisor.MontgomeryOne;
|
||
ulong baseVal = divisor.MontgomeryTwo;
|
||
|
||
if (exponent == 0UL)
|
||
{
|
||
return result.MontgomeryMultiply(1UL, modulus, nPrime);
|
||
}
|
||
|
||
const int WindowSize = 5;
|
||
Span<ulong> oddPowers = stackalloc ulong[1 << (WindowSize - 1)];
|
||
oddPowers[0] = baseVal;
|
||
ulong baseSquared = baseVal.MontgomeryMultiply(baseVal, modulus, nPrime);
|
||
for (int i = 1; i < oddPowers.Length; i++)
|
||
{
|
||
oddPowers[i] = oddPowers[i - 1].MontgomeryMultiply(baseSquared, modulus, nPrime);
|
||
}
|
||
|
||
int bitIndex = 63 - BitOperations.LeadingZeroCount(exponent);
|
||
|
||
while (bitIndex >= 0)
|
||
{
|
||
if (((exponent >> bitIndex) & 1UL) == 0UL)
|
||
{
|
||
result = result.MontgomeryMultiply(result, modulus, nPrime);
|
||
bitIndex--;
|
||
continue;
|
||
}
|
||
|
||
int windowStart = Math.Max(bitIndex - WindowSize + 1, 0);
|
||
ulong windowValue = (exponent >> windowStart) & ((1UL << (bitIndex - windowStart + 1)) - 1UL);
|
||
|
||
while ((windowValue & 1UL) == 0UL)
|
||
{
|
||
windowValue >>= 1;
|
||
windowStart++;
|
||
}
|
||
|
||
int squares = bitIndex - windowStart + 1;
|
||
for (int i = 0; i < squares; i++)
|
||
{
|
||
result = result.MontgomeryMultiply(result, modulus, nPrime);
|
||
}
|
||
|
||
result = result.MontgomeryMultiply(oddPowers[(int)(windowValue >> 1)], modulus, nPrime);
|
||
bitIndex = windowStart - 1;
|
||
}
|
||
|
||
return result.MontgomeryMultiply(1UL, modulus, nPrime);
|
||
}
|
||
|
||
private static ulong Pow2ModBinary(ulong exponent, ulong modulus)
|
||
{
|
||
if (modulus <= 1UL || (modulus & 1UL) == 0UL)
|
||
{
|
||
return 0UL;
|
||
}
|
||
|
||
ulong result = 1UL % modulus;
|
||
ulong baseVal = 2UL % modulus;
|
||
ulong remainingExponent = exponent;
|
||
|
||
while (remainingExponent > 0UL)
|
||
{
|
||
if ((remainingExponent & 1UL) != 0UL)
|
||
{
|
||
result = MultiplyMod(result, baseVal, modulus);
|
||
}
|
||
|
||
remainingExponent >>= 1;
|
||
if (remainingExponent == 0UL)
|
||
{
|
||
break;
|
||
}
|
||
|
||
baseVal = MultiplyMod(baseVal, baseVal, modulus);
|
||
}
|
||
|
||
return result;
|
||
}
|
||
|
||
private static ulong Pow2ModPrecomputedTable(ulong exponent, ulong modulus)
|
||
{
|
||
if (modulus <= 1UL || (modulus & 1UL) == 0UL)
|
||
{
|
||
return 0UL;
|
||
}
|
||
|
||
if (exponent == 0UL)
|
||
{
|
||
return 1UL % modulus;
|
||
}
|
||
|
||
Span<ulong> powers = stackalloc ulong[64];
|
||
powers[0] = 2UL % modulus;
|
||
int highestBit = 63 - BitOperations.LeadingZeroCount(exponent);
|
||
|
||
for (int index = 1; index <= highestBit; index++)
|
||
{
|
||
powers[index] = MultiplyMod(powers[index - 1], powers[index - 1], modulus);
|
||
}
|
||
|
||
ulong result = 1UL % modulus;
|
||
ulong remainingExponent = exponent;
|
||
int bitIndex = 0;
|
||
|
||
while (remainingExponent > 0UL)
|
||
{
|
||
if ((remainingExponent & 1UL) != 0UL)
|
||
{
|
||
result = MultiplyMod(result, powers[bitIndex], modulus);
|
||
}
|
||
|
||
remainingExponent >>= 1;
|
||
bitIndex++;
|
||
}
|
||
|
||
return result;
|
||
}
|
||
|
||
private static ulong Pow2ModBigInteger(ulong exponent, ulong modulus)
|
||
{
|
||
if (modulus <= 1UL || (modulus & 1UL) == 0UL)
|
||
{
|
||
return 0UL;
|
||
}
|
||
|
||
BigInteger mod = modulus;
|
||
BigInteger result = BigInteger.ModPow(2, exponent, mod);
|
||
return (ulong)result;
|
||
}
|
||
|
||
private static ulong MultiplyMod(ulong x, ulong y, ulong modulus)
|
||
{
|
||
UInt128 product = (UInt128)x * y;
|
||
return (ulong)(product % modulus);
|
||
}
|
||
}
|