feat: add C implementation for math/base/special/rempio2

[gunjjoshi]

Description

What is the purpose of this pull request?

This pull request:

• adds C implementation for math/base/special/rempio2.

Related Issues

Does this pull request have any related issues?

This pull request:

• resolves a part of [RFC]: Add C implementations to base special math functions (tracking issue) #649.

Questions

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No.

Other

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This is a draft PR, to discuss the implementation.

Checklist

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• Read, understood, and followed the contributing guidelines.

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@stdlib-js/reviewers

[gunjjoshi]

I was getting failure in some of the test cases. I have referred to FreeBSD version 12.2.0, as a reference.

rempio2: https://svnweb.freebsd.org/base/release/12.2.0/lib/msun/src/e_rem_pio2.c?revision=367086&view=markup
kernel-rempio2: https://svnweb.freebsd.org/base/release/12.2.0/lib/msun/src/k_rem_pio2.c?revision=367086&view=markup

Specifically, if we can check main.c, addon.c and native.js, that would help us out in completing this.

[kgryte]

@gunjjoshi I refactored the addon (see 0df78ac). Tests now pass; however, results for C and JS differ. Currently, if provided 128.0, JS returns ~3.618e-17 and C returns -1.6380356615247201e-19. You'll want to investigate why this is the case.

[gunjjoshi]

@gunjjoshi I refactored the addon (see 0df78ac). Tests now pass; however, results for C and JS differ. Currently, if provided 128.0, JS returns ~3.618e-17 and C returns -1.6380356615247201e-19. You'll want to investigate why this is the case.

Great, thanks for the help! I'll go through the implementation once more to check everything.

[gunjjoshi]

@kgryte I was able to track down the problem. This was because in the C implementation, earlier the exponent mask the we used had a value of 0x7ff00000. But in the javascript implementation, we were using 0x7ff.

After the changes, both the implementations give the same result for 128.0, i.e., ~3.618e-17.

Also, the lint error that we currently have is arising due to two similar if conditions, but that is required for our implementation.

[gunjjoshi]

There is a lint error saying the arrays are uninitialized. So, should we initialize them with zeros at the time of declaration directly, or should we declare them first, then initialize them with zeros using a for loop later?

[kgryte]

@gunjjoshi I'd go ahead and initialize with zeros at the time of declaration.

[Planeshifter]

Let's get this in to unblock additional C implementation work. Will merge once CI has passed.

Thanks, @gunjjoshi, for your work on it!

[gunjjoshi]

Thanks @Planeshifter @kgryte for helping in this.