Simplify BigInteger.Multiply #98587
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Simplify BigInteger.Multiply #98587
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Tagging subscribers to this area: @dotnet/area-system-numerics Issue DetailsIn my previous pull request #92208, I split BigIntegerCalculator.Multiply into two methods: MultiplyNearLength and MultiplyFarLength. The reason for this division is that BenchmarkBenchmarkSwitcher.FromAssembly(typeof(Tests).Assembly).Run(args);
public class Tests
{
public IEnumerable<object> GetMultiplyArgs()
{
Random random = new Random(227);
var lengths = new int[] { 1000, 10000, 100000, 1000000 };
for (int i = lengths.Length - 1; i >= 0; i--)
{
var largeBytes = MakeBytes(random, lengths[i]);
var large = new BigInteger(largeBytes, isUnsigned: true);
{
var smallBytes = MakeBytes(random, lengths[i] / 2);
var small = new BigInteger(smallBytes, isUnsigned: true);
yield return new Data($"{largeBytes.Length:D7}-{smallBytes.Length:D7}", large, small);
}
for (int j = i; j >= 0; j--)
{
var smallBytes = MakeBytes(random, lengths[j]);
var small = new BigInteger(smallBytes, isUnsigned: true);
yield return new Data($"{largeBytes.Length:D7}-{smallBytes.Length:D7}", large, small);
}
}
static byte[] MakeBytes(Random random, int length)
{
var bytes = new byte[length];
random.NextBytes(bytes);
return bytes;
}
}
public record Data(string Name, BigInteger Large, BigInteger Small)
{
public override string ToString() => Name;
}
[Benchmark]
[ArgumentsSource(nameof(GetMultiplyArgs))]
public BigInteger Multiply(Data data)
{
return data.Large * data.Small;
}
}
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Co-authored-by: Tanner Gooding <[email protected]>
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In my previous pull request #92208, I split BigIntegerCalculator.Multiply into two methods: MultiplyNearLength and MultiplyFarLength.
However, this division resulted in a lot of code duplication.
The reason for this division is that
coreLengthcan be greater thanbits.Length - n. Actually,core.Slice(0, ActualLength(core))seems to be sufficient sinceActualLength(core))is never greater thanbits.Length - n.https://github.com/kzrnm/dotnet-runtime/blob/f7eaf3b17fb4bd753b3404f0c9977c9693a2b480/src/libraries/System.Runtime.Numerics/src/System/Numerics/BigIntegerCalculator.SquMul.cs#L282-L326
Benchmark