feat: add math/base/special/atanhf

[nakul-krishnakumar]

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Resolves a part of #649 .

Description

What is the purpose of this pull request?

This pull request:

• Adds math/base/special/atanhf.

Related Issues

Does this pull request have any related issues?

This pull request has the following related issues:

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

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No.

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@stdlib-js/reviewers

[nakul-krishnakumar]

I was not able to pass all tests, but I could not figure out what part of the implementation was wrong. It would be really helpful if someone could help me fix it. I have attached the failing test cases below ( v - actual, e - expected ):

If I am not wrong, it is failing for this branch of the implementation:

	if ( x < HALF ) {
		t = f32( x + x );
		t = f32( HALF * log1pf( t + f32( t * f32( x / f32( ONE-x ) ) ) ) );

Reference Implementation:
https://svnweb.freebsd.org/base/release/9.3.0/lib/msun/src/e_atanhf.c?view=markup

[Neerajpathak07]

@nakul-krishnakumar normally when the test cases fail for smaller margins between the actual and expected values then there are 2 things to look after.

1. The package( atanhf ) was not implemented correctly according to the upstream implementation.
2. The test cases need to be looked after closely, check whether float64ToFloat32 is wrapped properly around elements and gives out value inside the precision limit.

@anandkaranubc correct me if I am missing something!!

[nakul-krishnakumar]

@nakul-krishnakumar normally when the test cases fail for smaller margins between the actual and expected values then there are 2 things to look after.

1. The package( atanhf ) was not implemented correctly according to the upstream implementation.

2. The test cases need to be looked after closely, check whether `float64ToFloat32` is wrapped properly around elements and gives out value inside the precision limit.

@anandkaranubc correct me if I am missing something!!

Okay, I will have a closer look around the above mentioned areas, thank you for the help! ❤️