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Fix BFloat16.Significand to be byte-sized and correct TryWriteSignificand methods #123288

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Merged
tannergooding merged 7 commits into from
Jan 19, 2026
Merged

Fix BFloat16.Significand to be byte-sized and correct TryWriteSignificand methods #123288

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1124773
Initial plan
Copilot Jan 16, 2026
147a9a9
Fix BFloat16 TryWriteSignificand methods and add tests
Copilot Jan 16, 2026
2d899b6
Refactor tests to use [Theory] with [InlineData]
Copilot Jan 16, 2026
b44d1de
Fix test data to use BFloat16 constants instead of float conversions
Copilot Jan 17, 2026
062a536
Use collection literal syntax for test data
Copilot Jan 17, 2026
84166d8
Update BFloat16Tests.cs
EgorBo Jan 17, 2026
ca5fb35
Change BFloat16.Significand from ushort to byte
Copilot Jan 17, 2026
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16 changes: 9 additions & 7 deletions src/libraries/System.Private.CoreLib/src/System/Numerics/BFloat16.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -116,11 +116,11 @@ internal sbyte Exponent
}
}

internal ushort Significand
internal byte Significand
{
get
{
return (ushort)(TrailingSignificand | ((BiasedExponent != 0) ? (1U << BiasedExponentShift) : 0U));
return (byte)(TrailingSignificand | ((BiasedExponent != 0) ? (1U << BiasedExponentShift) : 0U));
}
}

Expand Down Expand Up @@ -1010,7 +1010,7 @@ int IFloatingPoint<BFloat16>.GetExponentShortestBitLength()
}

/// <inheritdoc cref="IFloatingPoint{TSelf}.GetSignificandByteCount()" />
int IFloatingPoint<BFloat16>.GetSignificandByteCount() => sizeof(ushort);
int IFloatingPoint<BFloat16>.GetSignificandByteCount() => sizeof(byte);

/// <inheritdoc cref="IFloatingPoint{TSelf}.GetSignificandBitLength()" />
int IFloatingPoint<BFloat16>.GetSignificandBitLength() => SignificandLength;
Expand Down Expand Up @@ -1046,9 +1046,10 @@ bool IFloatingPoint<BFloat16>.TryWriteExponentLittleEndian(Span<byte> destinatio
/// <inheritdoc cref="IFloatingPoint{TSelf}.TryWriteSignificandBigEndian(Span{byte}, out int)" />
bool IFloatingPoint<BFloat16>.TryWriteSignificandBigEndian(Span<byte> destination, out int bytesWritten)
{
if (BinaryPrimitives.TryWriteUInt16BigEndian(destination, Significand))
if (destination.Length >= sizeof(byte))
{
bytesWritten = sizeof(uint);
destination[0] = Significand;
bytesWritten = sizeof(byte);
return true;
}

Expand All @@ -1059,9 +1060,10 @@ bool IFloatingPoint<BFloat16>.TryWriteSignificandBigEndian(Span<byte> destinatio
/// <inheritdoc cref="IFloatingPoint{TSelf}.TryWriteSignificandLittleEndian(Span{byte}, out int)" />
bool IFloatingPoint<BFloat16>.TryWriteSignificandLittleEndian(Span<byte> destination, out int bytesWritten)
{
if (BinaryPrimitives.TryWriteUInt16LittleEndian(destination, Significand))
if (destination.Length >= sizeof(byte))
{
bytesWritten = sizeof(uint);
destination[0] = Significand;
bytesWritten = sizeof(byte);
return true;
}

Expand Down
60 changes: 60 additions & 0 deletions src/libraries/System.Runtime/tests/System.Runtime.Tests/System/Numerics/BFloat16Tests.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -2271,6 +2271,66 @@ public static void RadiansToDegreesTest(BFloat16 value, BFloat16 expectedResult,
AssertEqual(+expectedResult, BFloat16.RadiansToDegrees(+value), allowedVariance);
}

public static IEnumerable<object[]> TryWriteSignificandBigEndianTest_TestData() =>
[
[BFloat16.NegativeInfinity, 1, new byte[] { 0x80 }],
[BFloat16.MinValue, 1, new byte[] { 0xFF }],
[(BFloat16)(-1.0f), 1, new byte[] { 0x80 }],
[-BFloat16.Epsilon, 1, new byte[] { 0x01 }],
[BFloat16.NaN, 1, new byte[] { 0xC0 }],
[(BFloat16)0.0f, 1, new byte[] { 0x00 }],
[(BFloat16)1.0f, 1, new byte[] { 0x80 }],
[BFloat16.MaxValue, 1, new byte[] { 0xFF }],
[BFloat16.PositiveInfinity, 1, new byte[] { 0x80 }],
];

[Theory]
[MemberData(nameof(TryWriteSignificandBigEndianTest_TestData))]
public static void TryWriteSignificandBigEndianTest(BFloat16 value, int expectedBytesWritten, byte[] expectedBytes)
{
Span<byte> destination = [0];
Assert.True(FloatingPointHelper<BFloat16>.TryWriteSignificandBigEndian(value, destination, out int bytesWritten));
Assert.Equal(expectedBytesWritten, bytesWritten);
Assert.Equal(expectedBytes, destination.ToArray());
}

[Fact]
public static void TryWriteSignificandBigEndianTest_EmptyDestination()
{
Assert.False(FloatingPointHelper<BFloat16>.TryWriteSignificandBigEndian(default, Span<byte>.Empty, out int bytesWritten));
Assert.Equal(0, bytesWritten);
}

public static IEnumerable<object[]> TryWriteSignificandLittleEndianTest_TestData() =>
[
[BFloat16.NegativeInfinity, 1, new byte[] { 0x80 }],
[BFloat16.MinValue, 1, new byte[] { 0xFF }],
[(BFloat16)(-1.0f), 1, new byte[] { 0x80 }],
[-BFloat16.Epsilon, 1, new byte[] { 0x01 }],
[BFloat16.NaN, 1, new byte[] { 0xC0 }],
[(BFloat16)0.0f, 1, new byte[] { 0x00 }],
[(BFloat16)1.0f, 1, new byte[] { 0x80 }],
[BFloat16.MaxValue, 1, new byte[] { 0xFF }],
[BFloat16.PositiveInfinity, 1, new byte[] { 0x80 }],
];

[Theory]
[MemberData(nameof(TryWriteSignificandLittleEndianTest_TestData))]
public static void TryWriteSignificandLittleEndianTest(BFloat16 value, int expectedBytesWritten, byte[] expectedBytes)
{
Span<byte> destination = [0];
Assert.True(FloatingPointHelper<BFloat16>.TryWriteSignificandLittleEndian(value, destination, out int bytesWritten));
Assert.Equal(expectedBytesWritten, bytesWritten);
Assert.Equal(expectedBytes, destination.ToArray());
}

[Fact]
public static void TryWriteSignificandLittleEndianTest_EmptyDestination()
{
Assert.False(FloatingPointHelper<BFloat16>.TryWriteSignificandLittleEndian(default, Span<byte>.Empty, out int bytesWritten));
Assert.Equal(0, bytesWritten);
}

#region AssertExtentions
static bool IsNegativeZero(BFloat16 value)
{
Expand Down
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