Add stein gcd
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This commit is contained in:
Timothy Warren 2020-02-28 17:11:36 -05:00
parent 57526e5fed
commit 096373789b
3 changed files with 47 additions and 12 deletions

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@ -66,16 +66,33 @@ fn bench_gcd(c: &mut Criterion) {
let small = Gcd::new(14, 15); let small = Gcd::new(14, 15);
for input in [small, med, max].iter() { for input in [small, med, max].iter() {
group.bench_with_input(BenchmarkId::new("Binary", input.left), input, |bench, input| { group.bench_with_input(
BenchmarkId::new("Binary", input.left),
input,
|bench, input| {
let a = input.left_fib; let a = input.left_fib;
let b = input.right_fib; let b = input.right_fib;
bench.iter(|| u128::gcd(black_box(a), black_box(b))) bench.iter(|| u128::gcd(black_box(a), black_box(b)))
}); },
group.bench_with_input(BenchmarkId::new("Euclid", input.left), input, |bench, input| { );
group.bench_with_input(
BenchmarkId::new("Stein", input.left),
input,
|bench, input| {
let a = input.left_fib;
let b = input.right_fib;
bench.iter(|| u128::stein_gcd(black_box(a), black_box(b)))
},
);
group.bench_with_input(
BenchmarkId::new("Euclid", input.left),
input,
|bench, input| {
let a = input.left_fib; let a = input.left_fib;
let b = input.right_fib; let b = input.right_fib;
bench.iter(|| u128::e_gcd(black_box(a), black_box(b))) bench.iter(|| u128::e_gcd(black_box(a), black_box(b)))
}); },
);
} }
group.finish(); group.finish();
} }

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@ -2,6 +2,7 @@
//! //!
//! Home to the numeric trait chain of doom, aka `Unsigned` //! Home to the numeric trait chain of doom, aka `Unsigned`
#![allow(unused_comparisons)] #![allow(unused_comparisons)]
use core::cmp::{max, min};
use core::convert::TryFrom; use core::convert::TryFrom;
use core::fmt::Debug; use core::fmt::Debug;
use core::ops::{ use core::ops::{
@ -113,6 +114,9 @@ pub trait Unsigned:
/// Euclid gcd algorithm /// Euclid gcd algorithm
fn e_gcd(a: Self, b: Self) -> Self; fn e_gcd(a: Self, b: Self) -> Self;
/// Stein gcd algorithm
fn stein_gcd(a: Self, b: Self) -> Self;
/// Find the least common multiple of two numbers /// Find the least common multiple of two numbers
fn lcm(a: Self, b: Self) -> Self; fn lcm(a: Self, b: Self) -> Self;
} }
@ -221,6 +225,20 @@ macro_rules! impl_unsigned {
x x
} }
fn stein_gcd(a: Self, b: Self) -> Self {
match ((a, b), (a & 1, b & 1)) {
((x, y), _) if x == y => y,
((0, x), _) | ((x, 0), _) => x,
((x, y), (0, 1)) | ((y, x), (1, 0)) => Self::stein_gcd(x >> 1, y),
((x, y), (0, 0)) => Self::stein_gcd(x >> 1, y >> 1) << 1,
((x, y), (1, 1)) => {
let (x, y) = (min(x, y), max(x, y));
Self::stein_gcd((y - x) >> 1, x)
}
_ => unreachable!(),
}
}
fn lcm(a: $Type, b: $Type) -> $Type { fn lcm(a: $Type, b: $Type) -> $Type {
if (a == 0 && b == 0) { if (a == 0 && b == 0) {
return 0; return 0;
@ -232,7 +250,6 @@ macro_rules! impl_unsigned {
)* )*
}; };
} }
impl_empty!( impl_empty!(
Num, Num,
(i8, u8, i16, u16, i32, u32, i64, u64, i128, u128, isize, usize) (i8, u8, i16, u16, i32, u32, i64, u64, i128, u128, isize, usize)
@ -271,6 +288,7 @@ mod tests {
assert_eq!(u8::gcd(2, 8), 2); assert_eq!(u8::gcd(2, 8), 2);
assert_eq!(u16::gcd(36, 48), 12); assert_eq!(u16::gcd(36, 48), 12);
assert_eq!(u16::e_gcd(36, 48), 12); assert_eq!(u16::e_gcd(36, 48), 12);
assert_eq!(u16::stein_gcd(36, 48), 12);
} }
#[test] #[test]

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@ -67,7 +67,7 @@ fn zero_denom() {
#[test] #[test]
fn fraction_reducing() { fn fraction_reducing() {
assert_eq!(frac!(1u8/2), Frac::new_unreduced(48u8, 96u8).reduce()); assert_eq!(frac!(1u8 / 2), Frac::new_unreduced(48u8, 96u8).reduce());
} }
#[test] #[test]