46 lines
1.8 KiB
C#
46 lines
1.8 KiB
C#
using System.Numerics;
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using PeterO.Numbers;
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namespace PerfectNumbers.Core;
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public static class RationalHelper
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{
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public static ERational FromDoubleRounded(double value, int scale = 100)
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{
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long numerator = checked((long)Math.Round(value * scale));
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long denominator = scale;
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long gcd = (long)BigInteger.GreatestCommonDivisor(numerator, denominator);
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// TODO: Replace the BigInteger-based GCD with the UInt128-friendly binary GCD helper so this rounding path avoids
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// allocating big integers for hot rational conversions.
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return ERational.Create(EInteger.FromInt64(numerator / gcd), EInteger.FromInt64(denominator / gcd));
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}
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public static EInteger ToEInteger(BigInteger value)
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{
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// TODO: Cache a reusable byte buffer here so converting to EInteger no longer allocates per call when parsing alpha
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// tables.
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return EInteger.FromBytes(value.ToByteArray(), true);
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}
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public static ulong FloorToUInt64(ERational value)
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{
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EInteger ei = value.ToEInteger();
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// TODO: Inline this floor conversion with the span-based ladder that dominated
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// ResidueComputationBenchmarks so the CPU path skips the expensive ERational ->
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// EInteger materialization when reducing large 2kp+1 divisors.
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return ei.ToUInt64Checked();
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}
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public static ulong CeilingToUInt64(ERational value)
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{
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EInteger ei = value.ToEInteger();
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if (value.CompareTo(ERational.Create(ei, EInteger.One)) > 0)
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ei += EInteger.One;
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// TODO: Replace this ceiling branch with the branchless adjustment measured fastest
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// in ResidueComputationBenchmarks so large-divisor scans avoid repeated ERational
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// conversions on the CPU hot path.
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return ei.ToUInt64Checked();
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}
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}
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