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Split FormatBigInteger into smaller parts. #112413

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Split FormatBigInteger into smaller parts. #112413

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58 changes: 33 additions & 25 deletions src/libraries/System.Runtime.Numerics/src/System/Number.BigInteger.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -748,7 +748,6 @@ internal static bool TryFormatBigInteger(BigInteger value, ReadOnlySpan<char> fo
{
Debug.Assert(formatString == null || formatString.Length == formatSpan.Length);

const uint TenPowMaxPartial = PowersOf1e9.TenPowMaxPartial;
const int MaxPartialDigits = PowersOf1e9.MaxPartialDigits;

int digits = 0;
Expand Down Expand Up @@ -795,30 +794,8 @@ internal static bool TryFormatBigInteger(BigInteger value, ReadOnlySpan<char> fo
stackalloc uint[cuMax] :
(bufferToReturn = ArrayPool<uint>.Shared.Rent(cuMax));

int cuDst = 0;

for (int iuSrc = cuSrc; --iuSrc >= 0;)
{
uint uCarry = value._bits[iuSrc];
for (int iuDst = 0; iuDst < cuDst; iuDst++)
{
Debug.Assert(base1E9Buffer[iuDst] < TenPowMaxPartial);

// Use X86Base.DivRem when stable
ulong uuRes = NumericsHelpers.MakeUInt64(base1E9Buffer[iuDst], uCarry);
(ulong quo, ulong rem) = Math.DivRem(uuRes, TenPowMaxPartial);
uCarry = (uint)quo;
base1E9Buffer[iuDst] = (uint)rem;
}
if (uCarry != 0)
{
(uCarry, base1E9Buffer[cuDst++]) = Math.DivRem(uCarry, TenPowMaxPartial);
if (uCarry != 0)
base1E9Buffer[cuDst++] = uCarry;
}
}

ReadOnlySpan<uint> base1E9Value = base1E9Buffer[..cuDst];
BigIntegerToBase1E9(value._bits, base1E9Buffer, out int base1E9Written);
ReadOnlySpan<uint> base1E9Value = base1E9Buffer[..base1E9Written];

int valueDigits = (base1E9Value.Length - 1) * MaxPartialDigits + FormattingHelpers.CountDigits(base1E9Value[^1]);

Expand Down Expand Up @@ -920,6 +897,37 @@ internal static bool TryFormatBigInteger(BigInteger value, ReadOnlySpan<char> fo
return strResult;
}

private static void BigIntegerToBase1E9(ReadOnlySpan<uint> bits, Span<uint> base1E9Buffer, out int leadingWritten)
{
leadingWritten = 0;

for (int iuSrc = bits.Length; --iuSrc >= 0;)
{
uint uCarry = bits[iuSrc];
for (int iuDst = 0; iuDst < leadingWritten; iuDst++)
{
Debug.Assert(base1E9Buffer[iuDst] < PowersOf1e9.TenPowMaxPartial);

(uCarry, base1E9Buffer[iuDst]) = DivRemTenPowMaxPartial(base1E9Buffer[iuDst], uCarry);
}
if (uCarry != 0)
{
(uCarry, base1E9Buffer[leadingWritten++]) = Math.DivRem(uCarry, PowersOf1e9.TenPowMaxPartial);
if (uCarry != 0)
base1E9Buffer[leadingWritten++] = uCarry;
}
}

[MethodImpl(MethodImplOptions.AggressiveInlining)]
static (uint, uint) DivRemTenPowMaxPartial(uint hi, uint lo)
{
// Use X86Base.DivRem when stable
ulong v = NumericsHelpers.MakeUInt64(hi, lo);
(ulong quo, ulong rem) = Math.DivRem(v, PowersOf1e9.TenPowMaxPartial);
return ((uint)quo, (uint)rem);
}
}

private static unsafe TChar* BigIntegerToDecChars<TChar>(TChar* bufferEnd, ReadOnlySpan<uint> base1E9Value, int digits)
where TChar : unmanaged, IUtfChar<TChar>
{
Expand Down
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