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

[gunjjoshi]

Description

What is the purpose of this pull request?

This pull request:

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

double stdlib_base_factorial( const double x );

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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No.

Checklist

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• Read, understood, and followed the contributing guidelines.

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@stdlib-js/reviewers

[kgryte]

@gunjjoshi We should amend the signature to be

double stdlib_base_factorial( const int32_t x );

Having double precision input in C doesn't make sense for this package.

[gunjjoshi]

@gunjjoshi We should amend the signature to be

double stdlib_base_factorial( const int32_t x );

Having double precision input in C doesn't make sense for this package.

Sure, I'll update this.

[gunjjoshi]

@gunjjoshi We should amend the signature to be

double stdlib_base_factorial( const int32_t x );

Having double precision input in C doesn't make sense for this package.

@kgryte Wouldn't this lead to different behaviors in C and JavaScript? For instance, currently:

var v = factorial( 0.5 );
// returns ~0.886

But, in C, this won't be possible, as we will have only integers as input.

[kgryte]

Ah wait. You're right. I forgot about the gamma approximation. Disregard my comment

[Planeshifter]

Looks all well; will merge shortly.