feat: add math/base/special/erff

[officiallyanee]

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Resolves #729 .

Description

What is the purpose of this pull request?

This pull request:

• adds C & JS implementation for math/base/special/erff.

Related Issues

Does this pull request have any related issues?

This pull request has the following related issues:

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

Questions

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No.

Other

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No.

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• Read, understood, and followed the contributing guidelines.

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used for understanding https://svnweb.freebsd.org/base/release/12.2.0/lib/msun/src/s_erff.c?view=markup

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[stdlib-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
math/base/special/erff	$\color{red}666/678$ $\color{green}+0.00%$	$\color{red}50/56$ $\color{green}+0.00%$	$\color{green}9/9$ $\color{green}+0.00%$	$\color{red}666/678$ $\color{green}+0.00%$

The above coverage report was generated for the changes in this PR.

[officiallyanee]

/stdlib update-copyright-years

[gunjjoshi]

Thanks for working on this, @officiallyanee. We can revisit this PR once @stdlib/math/base/special/expf is implemented.

[gunjjoshi]

@officiallyanee We do not directly use these constant declarations and initializations as given in the reference implementation, like what you have done here. Instead, you can follow how we do the same thing in the double-precision implementation, i.e., in https://github.com/stdlib-js/stdlib/blob/develop/lib/node_modules/%40stdlib/math/base/special/erf/src/main.c#L41

[gunjjoshi]

Same comment for all these constants. See https://github.com/stdlib-js/stdlib/blob/develop/lib/node_modules/%40stdlib/math/base/special/erf/src/main.c#L45

[gunjjoshi]

This is not what we want. Instead, we need to use @stdlib/math/base/special/expf, once we have implemented it. Till we do not have expf, we might not be able to move forward with erff.

[officiallyanee]

hello thanks for your review,
i saw it being used for coshf that also depends on expf so i went ahead with it. Are there any particular usecases where its fine to use and where its not?