# fast_inv_sqrt
This was made purely for fun and testing crates.io publishing, but may actually be usable.
InvSqrt32 trait provide inv_sqrt32() function for primitive numeric types.
InvSqrt64 provides inv_sqrt64().
## How do I use it?
Cargo.toml:
```toml
[dependencies]
fast_inv_sqrt = "~1.0"
```
Code:
```rust
extern crate fast_inv_sqrt;
use fast_inv_sqrt::InvSqrt32;
use fast_inv_sqrt::InvSqrt64;
fn main() {
let f: f32 = 1.234;
println!("{}", f.inv_sqrt32());
let i: i8 = 55;
println!("{}", i.inv_sqrt64());
}
```
## Benchmarks
Benchmarks require nightly compiler.
"_ref_" benchmarks use f1 / f2.sqrt()
"_impl_" benchmarks use f1 * f2.inv_sqrtXX()
$ cargo bench --features 'nightly'
```
test test32::bench_plain_impl ... bench: 6 ns/iter (+/- 0)
test test32::bench_plain_ref ... bench: 13 ns/iter (+/- 0)
test test32::bench_real_impl ... bench: 6 ns/iter (+/- 0)
test test32::bench_real_ref ... bench: 13 ns/iter (+/- 0)
test test64::bench_plain_impl ... bench: 6 ns/iter (+/- 0)
test test64::bench_plain_ref ... bench: 20 ns/iter (+/- 0)
test test64::bench_real_impl ... bench: 6 ns/iter (+/- 0)
test test64::bench_real_ref ... bench: 20 ns/iter (+/- 0)
```
Feature 'omit-checking' disables checks of if value passed is_sign_positive() and
is_normal(), and will produce invalid results for denormalized and negative values,
but this is fast:
```
test test32::bench_plain_impl ... bench: 2 ns/iter (+/- 0)
test test32::bench_plain_ref ... bench: 13 ns/iter (+/- 0)
test test32::bench_real_impl ... bench: 3 ns/iter (+/- 0)
test test32::bench_real_ref ... bench: 13 ns/iter (+/- 0)
test test64::bench_plain_impl ... bench: 2 ns/iter (+/- 0)
test test64::bench_plain_ref ... bench: 20 ns/iter (+/- 0)
test test64::bench_real_impl ... bench: 3 ns/iter (+/- 0)
test test64::bench_real_ref ... bench: 20 ns/iter (+/- 0)
```