mkesper on 0x5f3759df and the fast inverse square root (2012)

Comment on 0x5f3759df and the fast inverse square root (2012)parent

So convert floating point to its integer representation.

Would something dirty like this be feasible in rust?

AFAICT transmute would work: http://rustbyexample.com/staging/unsafe.html

That's what's great about Rust, you can write unsafe code when you need it and it's isolated in `unsafe` blocks for easy auditing.

EDIT: Didn't test it too much, but looks like it works.

    fn fast_inv_sqrt(x: f32) -> f32 {
        let f: f32 = unsafe {
            let i: i32 = std::mem::transmute(x);
            std::mem::transmute(0x5f3759df - (i >> 1))
        };
        f * (1.5 - 0.5 * x * f * f)
    }

    println!("{}", fast_inv_sqrt(1.0));
      //=> 0.998307
    println!("{}", fast_inv_sqrt(255.0));
      //=> 0.062517

EDIT2: Shorter, more readable version.

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