Fix potential NaN from converting to Okhsl when the input is white or black

[Ogeon]

This turned out to be an error in the reference implementation as well, as I understand it. This line in the get_Cs function produces NaN when the lightness is 1.0 or 0.0, by dividing 0.0 by 0.0:

let k = C_max/Math.min((L*ST_max[0]), (1-L)*ST_max[1]);

The reference seem to be missing the necessary safeguards for this. I looked around for other implementations to see if they had the same issue, but didn't find anything so far. Regardless, it breaks down if it gets an Oklab value with lightness 1 or 0. Some inaccuracies or rounding made the chroma != 0.0, which bypassed the already added check for that and let the NaNs out.

Closed Issues

• Fixes Srgb -> Okhsl conversion results in NaN saturation #368

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (508f644) 80.62% compared to head (503f34c) 81.46%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #369      +/-   ##
==========================================
+ Coverage   80.62%   81.46%   +0.84%     
==========================================
  Files         113      113              
  Lines       18502    18438      -64     
  Branches    18502    18438      -64     
==========================================
+ Hits        14917    15021     +104     
+ Misses       3297     3220      -77     
+ Partials      288      197      -91     

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[codspeed-hq]

CodSpeed Performance Report

Merging #369 will improve performances by ×3.1

_{Comparing fix_issue_368 (503f34c) with master (508f644)}

Summary

⚡ 7 improvements
✅ 38 untouched benchmarks

Benchmarks breakdown

	Benchmark	master	fix_issue_368	Change
⚡	yxy to xyz	20 µs	13.2 µs	+50.98%
⚡	matrix_inverse	838.9 ns	271.1 ns	×3.1
⚡	xyz to yxy	18.4 µs	11.2 µs	+64.26%
⚡	multiply_3x3	427.8 ns	372.2 ns	+14.93%
⚡	hsv to hsl	29 µs	16 µs	+81.27%
⚡	hsl to hsv	20.5 µs	13.9 µs	+46.74%
⚡	hwb to hsv	18.3 µs	12.1 µs	+51.57%

[Ogeon]

bors r+

[Ogeon]

Oh, looks like bors has finally been disabled. 😞