Normalize a CSS z-index value to a 32-bit floating-point number

Origin

I struggled to map CSS z-index values to 32-bit floating-point numbers between 0.0 and 1.0 because dividing a large number by another large number, such as 2_147_483_646.0 / 2_147_483_647.0, does not yield precise results.

To illustrate the issue, here are some examples (see playground):

2_147_483_646.0 / 2_147_483_647.0 = 1.0
2_147_483_645.0 / 2_147_483_647.0 = 1.0
2_147_483_644.0 / 2_147_483_647.0 = 1.0
2_147_483_643.0 / 2_147_483_647.0 = 1.0
2_147_483_642.0 / 2_147_483_647.0 = 1.0
2_147_483_641.0 / 2_147_483_647.0 = 1.0
2_147_483_640.0 / 2_147_483_647.0 = 1.0
2_147_483_639.0 / 2_147_483_647.0 = 1.0
2_147_483_638.0 / 2_147_483_647.0 = 1.0
2_147_483_637.0 / 2_147_483_647.0 = 1.0

I spent some time experimenting to figure out a reasonable approach to this challenge, and I may have finally found a way to manage the headache of mapping CSS z-index values.

It's important to note that this approach is quite basic and does not guarantee 100% precision. In other words, further stress testing is necessary to ensure the reliability of this implementation.

Additionally, I haven't done any parameter tuning yet, so there could very well be a more efficient method to achieve this that I haven’t discovered.