BitConverter.HalfToInt16Bits(Half) result comparison issue

[gcsizmadia]

Description

I am playing around the negative zero number and I found an interesting thing while I used BitConverter.HalfToInt16(Half) method.

The two comparison gives different result

• Compare the method result directly to 0.
• Store the method result in a short variable then compare the variable to 0.

Reproduction Steps

Half half = (Half)(-0.0f);

// It will be -32768.
short bits = BitConverter.HalfToInt16Bits(half);

// It will be true.
bool isMethodResultGreaterThanOrEqualToZero = BitConverter.HalfToInt16Bits(half) >= 0;

// It will be false.
bool isVariableGreaterThanOrEqualToZero = bits >= 0;

Expected behavior

The expected behavior is that the two comparison method should have the same result: false

Actual behavior

• When directly check if the method result is >= 0 then the comparison result will be true.
• When storing the method result first in a variable and then check if the variable is >= 0 then the comparison result will be false.

Regression?

No response

Known Workarounds

No response

Configuration

• Which version of .NET is the code running on?
  .NET 6.0.14 and .NET 7.0.3
• What OS and version, and what distro if applicable?
  Windows 11 - Microsoft Windows [Version 10.0.22621.1265]
• What is the architecture (x64, x86, ARM, ARM64)?
  x64
• Do you know whether it is specific to that configuration?
  I don't know.

Other information

No response

[Clockwork-Muse]

I'm getting false for both.
Can you please write a small reproduction project that shows this issue?

[ghost]

Tagging subscribers to this area: @dotnet/area-system-numerics
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Description

I am playing around the negative zero number and I found an interesting thing while I used BitConverter.HalfToInt16(Half) method.

The two comparison gives different result

• Compare the method result directly to 0.
• Store the method result in a short variable then compare the variable to 0.

Reproduction Steps

Half half = (Half)(-0.0f);

// It will be -32768.
short bits = BitConverter.HalfToInt16Bits(half);

// It will be true.
bool isMethodResultGreaterThanOrEqualToZero = BitConverter.HalfToInt16Bits(half) >= 0;

// It will be false.
bool isVariableGreaterThanOrEqualToZero = bits >= 0;

Expected behavior

The expected behavior is that the two comparison method should have the same result: false

Actual behavior

• When directly check if the method result is >= 0 then the comparison result will be true.
• When storing the method result first in a variable and then check if the variable is >= 0 then the comparison result will be false.

Regression?

No response

Known Workarounds

No response

Configuration

• Which version of .NET is the code running on?
  .NET 6.0.14 and .NET 7.0.3
• What OS and version, and what distro if applicable?
  Windows 11 - Microsoft Windows [Version 10.0.22621.1265]
• What is the architecture (x64, x86, ARM, ARM64)?
  x64
• Do you know whether it is specific to that configuration?
  I don't know.

Other information

No response

Author:	gcsizmadia
Assignees:	-
Labels:	area-System.Numerics, untriaged
Milestone:	-

[gcsizmadia]

It seems that this issue applies only to .NET 6.0.14. In .NET 7.0.3 both values are false.

.NET 6.0.14

.NET 7.0.3

[gcsizmadia]

I attached a .zip file with a simple console app that targets both .net6.0 and .net7.0.

BitConverterTest.zip

[KeterSCP]

It also has different output for Debug and Release in .NET 6.0.14

Debug:

-32768
True
False

Release:

32768
True
True

[ghost]

Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch, @kunalspathak
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Description

I am playing around the negative zero number and I found an interesting thing while I used BitConverter.HalfToInt16(Half) method.

The two comparison gives different result

• Compare the method result directly to 0.
• Store the method result in a short variable then compare the variable to 0.

Reproduction Steps

Half half = (Half)(-0.0f);

// It will be -32768.
short bits = BitConverter.HalfToInt16Bits(half);

// It will be true.
bool isMethodResultGreaterThanOrEqualToZero = BitConverter.HalfToInt16Bits(half) >= 0;

// It will be false.
bool isVariableGreaterThanOrEqualToZero = bits >= 0;

Expected behavior

The expected behavior is that the two comparison method should have the same result: false

Actual behavior

• When directly check if the method result is >= 0 then the comparison result will be true.
• When storing the method result first in a variable and then check if the variable is >= 0 then the comparison result will be false.

Regression?

No response

Known Workarounds

No response

Configuration

• Which version of .NET is the code running on?
  .NET 6.0.14 and .NET 7.0.3
• What OS and version, and what distro if applicable?
  Windows 11 - Microsoft Windows [Version 10.0.22621.1265]
• What is the architecture (x64, x86, ARM, ARM64)?
  x64
• Do you know whether it is specific to that configuration?
  I don't know.

Other information

No response

Author:	gcsizmadia
Assignees:	-
Labels:	area-CodeGen-coreclr, untriaged
Milestone:	-

[JulieLeeMSFT]

@gcsizmadia, is there product impact with .NET 6.0.14? Can you work with .NET 7.0.3?

It seems that this issue applies only to .NET 6.0.14.

[gcsizmadia]

@JulieLeeMSFT, I'm working on a class library (nuget package) that targets both net6.0 and net7.0 as well and its functions must work on both, especially because .NET 6 is an LTS version that will stay longer with us than .NET 7.

So unless there is a workaround that can be applied to net6.0 target, it is a product impact.

[jakobbotsch]

This sounds like the same issue as #61359 that was fixed in .NET 7+ by #64881. I think we can backport that fix to .NET 6.

[JulieLeeMSFT]

Sounds good. Please check if it solves this problem and backport it.

This sounds like the same issue as #61359 that was fixed in .NET 7+ by #64881. I think we can backport that fix to .NET 6.

[jakobbotsch]

This was backported and the fix is available in 6.0.16 that was released on April 11th.