Improve performance of `rem_euclid()` for signed integers
such code is copy from
https://github.com/rust-lang/rust/blob/master/library/std/src/f32.rs and
https://github.com/rust-lang/rust/blob/master/library/std/src/f64.rs
using `r+rhs.abs()` is faster than calc it with an if clause. Bench result:
```
$ cargo bench
Compiling div-euclid v0.1.0 (/me/div-euclid)
Finished bench [optimized] target(s) in 1.01s
Running unittests src/lib.rs (target/release/deps/div_euclid-7a4530ca7817d1ef)
running 7 tests
test tests::it_works ... ignored
test tests::bench_aaabs ... bench: 10,498,793 ns/iter (+/- 104,360)
test tests::bench_aadefault ... bench: 11,061,862 ns/iter (+/- 94,107)
test tests::bench_abs ... bench: 10,477,193 ns/iter (+/- 81,942)
test tests::bench_default ... bench: 10,622,983 ns/iter (+/- 25,119)
test tests::bench_zzabs ... bench: 10,481,971 ns/iter (+/- 43,787)
test tests::bench_zzdefault ... bench: 11,074,976 ns/iter (+/- 29,633)
test result: ok. 0 passed; 0 failed; 1 ignored; 6 measured; 0 filtered out; finished in 19.35s
```
It seems that, default `rem_euclid` triggered a branch prediction, thus `bench_default` is faster than `bench_aadefault` and `bench_aadefault`, which shuffles the order of calculations. but all of them slower than what it was in `f64`'s and `f32`'s `rem_euclid`, thus I submit this PR.
bench code:
```rust
#![feature(test)]
extern crate test;
fn rem_euclid(a:i32,rhs:i32)->i32{
let r = a % rhs;
if r < 0 { r + rhs.abs() } else { r }
}
#[cfg(test)]
mod tests {
use super::*;
use test::Bencher;
use rand::prelude::*;
use rand::rngs::SmallRng;
const N:i32=1000;
#[test]
fn it_works() {
let a: i32 = 7; // or any other integer type
let b = 4;
let d:Vec<i32>=(-N..=N).collect();
let n:Vec<i32>=(-N..0).chain(1..=N).collect();
for i in &d {
for j in &n {
assert_eq!(i.rem_euclid(*j),rem_euclid(*i,*j));
}
}
assert_eq!(rem_euclid(a,b), 3);
assert_eq!(rem_euclid(-a,b), 1);
assert_eq!(rem_euclid(a,-b), 3);
assert_eq!(rem_euclid(-a,-b), 1);
}
#[bench]
fn bench_aaabs(b: &mut Bencher) {
let mut d:Vec<i32>=(-N..=N).collect();
let mut n:Vec<i32>=(-N..0).chain(1..=N).collect();
let mut rng=SmallRng::from_seed([1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,21]);
n.shuffle(&mut rng);
d.shuffle(&mut rng);
n.shuffle(&mut rng);
b.iter(||{
let mut res=0;
for i in &d {
for j in &n {
res+=rem_euclid(*i,*j);
}
}
res
});
}
#[bench]
fn bench_aadefault(b: &mut Bencher) {
let mut d:Vec<i32>=(-N..=N).collect();
let mut n:Vec<i32>=(-N..0).chain(1..=N).collect();
let mut rng=SmallRng::from_seed([1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,21]);
n.shuffle(&mut rng);
d.shuffle(&mut rng);
n.shuffle(&mut rng);
b.iter(||{
let mut res=0;
for i in &d {
for j in &n {
res+=i.rem_euclid(*j);
}
}
res
});
}
#[bench]
fn bench_abs(b: &mut Bencher) {
let d:Vec<i32>=(-N..=N).collect();
let n:Vec<i32>=(-N..0).chain(1..=N).collect();
b.iter(||{
let mut res=0;
for i in &d {
for j in &n {
res+=rem_euclid(*i,*j);
}
}
res
});
}
#[bench]
fn bench_default(b: &mut Bencher) {
let d:Vec<i32>=(-N..=N).collect();
let n:Vec<i32>=(-N..0).chain(1..=N).collect();
b.iter(||{
let mut res=0;
for i in &d {
for j in &n {
res+=i.rem_euclid(*j);
}
}
res
});
}
#[bench]
fn bench_zzabs(b: &mut Bencher) {
let mut d:Vec<i32>=(-N..=N).collect();
let mut n:Vec<i32>=(-N..0).chain(1..=N).collect();
let mut rng=SmallRng::from_seed([1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,21]);
d.shuffle(&mut rng);
n.shuffle(&mut rng);
d.shuffle(&mut rng);
b.iter(||{
let mut res=0;
for i in &d {
for j in &n {
res+=rem_euclid(*i,*j);
}
}
res
});
}
#[bench]
fn bench_zzdefault(b: &mut Bencher) {
let mut d:Vec<i32>=(-N..=N).collect();
let mut n:Vec<i32>=(-N..0).chain(1..=N).collect();
let mut rng=SmallRng::from_seed([1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,21]);
d.shuffle(&mut rng);
n.shuffle(&mut rng);
d.shuffle(&mut rng);
b.iter(||{
let mut res=0;
for i in &d {
for j in &n {
res+=i.rem_euclid(*j);
}
}
res
});
}
}
```
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