How can I decode f16 to f32 using only the stable standard library?

Question

I need to convert stored half-floats (16 bits) to standard 32-bit floats. I am currently using the code below, but it relies on libc. I want to use only std , and it should work on stable Rust.

 #[inline] fn decode_f16(half: u16) -> f32 { let exp: u16 = half >> 10 & 0x1f; let mant: u16 = half & 0x3ff; let val: f32 = if exp == 0 { ffi::c_ldexpf(mant as f32, -24) } else if exp != 31 { ffi::c_ldexpf(mant as f32 + 1024f32, exp as isize - 25) } else if mant == 0 { ::std::f32::INFINITY } else { ::std::f32::NAN }; if half & 0x8000 != 0 { -val } else { val } } 

Answer 1

You can simply replace ffi::c_ldexpf(x, y) with x * (2.0).powi(y) . This works on all u16 s, according to my exhaustive test .