Rewrite BigInteger internals to use native-width (nuint) limbs#125799

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stephentoub wants to merge 27 commits intodotnet:mainfrom

stephentoub:biginteger-nuint-rewrite

Commits on Mar 18, 2026

Convert Number.BigInteger.cs from uint limbs to nuint limbs

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Convert BigInteger internal representation from uint to nuint limbs

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Fix SubWithBorrow sign-extension bug on 32-bit and update stale comments

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Use branchless underflow detection in SubtractDivisor

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Fuse two's complement conversion with bitwise AND/OR/XOR

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Cache PowersOf1e9 table for repeated ToString/Parse calls

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Tune Burnikel-Ziegler division threshold for 64-bit limbs

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Add property-based validation tests and fix BitwiseAnd sign bug

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Add edge-case tests for sign combos, SIMD boundaries, and coverage gaps

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Add Montgomery multiplication for ModPow with odd moduli

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Add tests for Barrett+FastReducer with even large moduli

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Add sliding window exponentiation and separate squaring thresholds

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Avoid array copy in GCD when one operand is zero

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Optimize GCD LehmerCore and DivRem to avoid Int128/UInt128 overhead

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Fix ToString Naive loop regression by processing 32-bit halves

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Fix small-operand, GCD LehmerCore, and ToByteArray regressions

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Add unrolled Mul1/MulAdd1/SubMul1 primitives for multiply and division inner loops

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Rewrite BigInteger internals to use native-width (nuint) limbs#125799

Rewrite BigInteger internals to use native-width (nuint) limbs#125799
stephentoub wants to merge 27 commits intodotnet:mainfrom
stephentoub:biginteger-nuint-rewrite

Commits on Mar 18, 2026

Convert Number.BigInteger.cs from uint limbs to nuint limbs

Convert BigInteger internal representation from uint to nuint limbs

Fix SubWithBorrow sign-extension bug on 32-bit and update stale comments

Use branchless underflow detection in SubtractDivisor

Fuse two's complement conversion with bitwise AND/OR/XOR

Cache PowersOf1e9 table for repeated ToString/Parse calls

Tune Burnikel-Ziegler division threshold for 64-bit limbs

Add property-based validation tests and fix BitwiseAnd sign bug

Add edge-case tests for sign combos, SIMD boundaries, and coverage gaps

Add Montgomery multiplication for ModPow with odd moduli

Add tests for Barrett+FastReducer with even large moduli

Add sliding window exponentiation and separate squaring thresholds

Avoid array copy in GCD when one operand is zero

Optimize GCD LehmerCore and DivRem to avoid Int128/UInt128 overhead

Fix ToString Naive loop regression by processing 32-bit halves

Fix small-operand, GCD LehmerCore, and ToByteArray regressions

Add unrolled Mul1/MulAdd1/SubMul1 primitives for multiply and division inner loops

Commits on Mar 19, 2026

Replace Unsafe.Add with span indexing using bounds hints for JIT elision

Use hardware intrinsics for BigMul, DivRem, and AddWithCarry primitives

Revert _sign from nint to int to eliminate small-value regressions

Use ulong arithmetic in PowCore when modulus fits in uint

Clean up formatting / style

Fix SubtractSelf callers to restore borrow==0 postcondition

Commits on Mar 20, 2026

Address PR feedback

Address feedback

Fix GetSignBitsIfValid XML doc to clarify 'valid hex digit and considered positive'

Add comment explaining nuint[] for base-1e9 intermediate representation