[RISC-V] Test HalfTest: fixed payload preservation testcase for RISC-V

[denis-paranichev]

Arithmetic operations with NaN does not preserve payload on RISC-V. And explicit conversion operators in Half class use arithmetic operations with float. That is why payload preservation test cases are failed for RISC-V.

This fixes payload preservation testcases in:

• System.Runtime.Tests.HalfTests.ExplicitConversion_FromSingle
• System.Runtime.Tests.HalfTests.ExplicitConversion_ToSingle

Part of #84834
cc @tannergooding @gbalykov @t-mustafin @clamp03 @tomeksowi

[denis-paranichev]

@tannergoodin, I found that float->half and double->half cast algorithms are not similar. Is there a reason for such difference?

[tannergooding]

Is there a reason for such difference?

The float->half version had a community member hand optimize it. The double->half version did not.

[denis-paranichev]

@tannergooding, @jkotas, can this PR be merged?

[tannergooding]

This should be BitConverter.DoubleToInt64Bits(expected) == BitConverter.DoubleToInt64Bits(actual)

[tannergooding]

and similarly for the ones further down. For float on .NET Framework, I'd just define a helper:

static unsafe int SingleToInt32Bits(float value)
{
    return *(int*)&value;
}

[denis-paranichev]

Done, thank you for suggestion. By the way I didn't find anything in the supported product list for the BitConverter.HalfToInt16Bits function in .NET API Catalog except the .NET version

[tannergooding]

The official API docs include the .NET versions its been included in: https://learn.microsoft.com/en-us/dotnet/api/system.bitconverter.halftoint16bits#applies-to

[denis-paranichev]

@tannergooding, seems like the remaining CI failures are not caused by PR, could you review please?

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Issue Details

---

Arithmetic operations with NaN does not preserve payload on RISC-V. And explicit conversion operators in Half class use arithmetic operations with float. That is why payload preservation test cases are failed for RISC-V.

This fixes payload preservation testcases in:

• System.Runtime.Tests.HalfTests.ExplicitConversion_FromSingle
• System.Runtime.Tests.HalfTests.ExplicitConversion_ToSingle

Part of #84834
cc @tannergooding @gbalykov @t-mustafin @clamp03 @tomeksowi

Author:	denis-paranichev
Assignees:	denis-paranichev
Labels:	area-System.Numerics, community-contribution, arch-riscv, needs-area-label
Milestone:	-

[denis-paranichev]

Thank you all for review!
@tannergooding, thank you for merge it!