Double.ToString with two section separators and negative zero placing additional negative sign in output

[fryguy1013]

Description

When using a string format with two section separators and a negative zeroish number when accounting for the limited number of decimal points, there is an additional negative sign added to the output string when there shouldn't be.

Reproduction Steps

Console.WriteLine((-0.001).ToString("+0.00;-0.00")); ,

Expected behavior

Outputs +0.00 on .NET Framework 4.7.2 (-0.00 seems valid as well)

Actual behavior

outputs -+0.00 on dotnet6

Regression?

This worked in .NET Framework 4.7.2.

Known Workarounds

The two-section "+0.00;-0.00" can be replaced by the three-section "+0.00;-0.00;+0.00" and seems to work correctly

Configuration

I've reproduced this in both my local visual studio and dotnetfiddle.net on dotnet 6.

Other information

This seems related to the bug #32237 which was an "Closed As Design" due to https://devblogs.microsoft.com/dotnet/floating-point-parsing-and-formatting-improvements-in-net-core-3-0/, but this issue seems like an actual regression since the string format is explicitly calling out how to format positive and negative numbers

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Issue Details

---

Description

When using a string format with two section separators and a negative zeroish number when accounting for the limited number of decimal points, there is an additional negative sign added to the output string when there shouldn't be.

Reproduction Steps

Console.WriteLine((-0.001).ToString("+0.00;-0.00")); ,

Expected behavior

Outputs +0.00 on .NET Framework 4.7.2 (-0.00 seems valid as well)

Actual behavior

outputs -+0.00 on dotnet6

Regression?

This worked in .NET Framework 4.7.2.

Known Workarounds

The two-section "+0.00;-0.00" can be replaced by the three-section "+0.00;-0.00;+0.00" and seems to work correctly

Configuration

I've reproduced this in both my local visual studio and dotnetfiddle.net on dotnet 6.

Other information

This seems related to the bug #32237 which was an "Closed As Design" due to https://devblogs.microsoft.com/dotnet/floating-point-parsing-and-formatting-improvements-in-net-core-3-0/, but this issue seems like an actual regression since the string format is explicitly calling out how to format positive and negative numbers

Author:	fryguy1013
Assignees:	-
Labels:	area-System.Numerics
Milestone:	-

[danmoseley]

This was "+0.00" in .NET Core 2.1 and changed to "-+0.00" in .NET Core 3.1

[tannergooding]

I'm guessing there is a conflict between the input value and the rounded value. Will take a look.

[jwosty]

Depending on your use case, it's possible to work around it using all three section separators, but you lose the ability to print negative and positive zero differently.

For example:

(-0.0).ToString("+0.0;-0.0;0.0")

and

(-0.0000001).ToString("+0.0;-0.0;0.0")

both display 0.0.

[fryguy1013]

The workaround we're using to preserve the behavior is in the issue. Your idea will display "0.0" instead of "+0.0" (or "-0.0") which isn't the right size since the protocol requires a sign bit in that position of the string.

[jwosty]

The workaround we're using to preserve the behavior is in the issue. Your idea will display "0.0" instead of "+0.0" (or "-0.0") which isn't the right size since the protocol requires a sign bit in that position of the string.

Ah, I see I didn't read that properly (it was late at night :) ). You're right, that is the better workaround. Any of these workaround using the third section still have the problem of not preserving the difference between -0.0 and +0.0 though -- therefore there is no real workaround if you really need that behavior (other than writing your own formatting code). A true fix would be great.

[tannergooding]

This is effectively a do anytime issue. The bug is small and shouldn't be overly difficult to fix. For the most part -0.0 needs to be treated as negative and distinct from +0.0 for the purposes of formatting.