Fix for Random failures in System.Numerics.Tests.modpowTest.ModPowAxiom test #74112
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ghost
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danmoseley
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Updated the title -- issue numbers in titles don't work well when looking at lists of PR's 😸 |
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.NET 7 port needed? |
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@danmoseley , I I think yes, .NET 7 port is needed because without the fix |
| @@ -464,7 +472,7 @@ private const | |||
| power >>= 1; | |||
| } | |||
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| return result.Slice(0, resultLength); | |||
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Was this slice basically unnecessary in all cases, and causing problems in this edge case?
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Yes, correct. It doesn't exist for overload of PowCore with exponent of arbitrary length.
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Removing this slice introduced a regression for the case of:
value: 174475926811173371108797680334274448482027679060635889276326576767485928691470272416521788770673419883076040463212449631887959313694345475337324466914914839368969988215395980439434099840700753576299320684517028939674493640310781015739837159625716992654178036326745036841619965661654305787656989089177185300627
exponent: 152266387011071825363527751452194927195391511201743678326712300944812006670853968954038119879530327815990523885596782666640476470053822766345969220504425389995206265094671158964311234812226260664473986637197447367726400093404731405598815953979171704175885394570388678952091206779039984338579147114424357147650
modulus: 15548277136038299103
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In this scenario, the length of result is greater than the length of bits and so the result.CopyTo(bits) operation fails as the destination is too short.
I expect the actual issue here is that resultLength isn't being correctly tracked somewhere.
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Its not that resultLength is incorrect, its that bits will have been mutated and may contain temporary data
src/libraries/System.Runtime.Numerics/src/System/Numerics/BigIntegerCalculator.PowMod.cs
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@danmoseley Yes, I'd like to get this in for .NET 7, as this is a regression from .NET 6. |
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/backport to release/7.0-rc1 |
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Started backporting to release/7.0-rc1: https://github.com/dotnet/runtime/actions/runs/2885517952 |
ghost
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Fixes #70330