Why have a custom sqrt implementation?

[JavaDerg]

Hey, I've been looking trough the code earlier to try understand how the rasterization process works,
while doing so I found this file: https://github.com/mooman219/fontdue/blob/master/src/platform/float/sqrt.rs

Can someone explain me what is the reasoning behind having your own sqrt implementation over the one provided by rust?

[mooman219]

Some platforms that fontdue compiles for don't support the standard library, so f32::sqrt isn't available.

[JavaDerg]

Thanks for answering ^^