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Define extended GCD, combined GCD+LCM - #19

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strake:gcd
Apr 25, 2019
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Define extended GCD, combined GCD+LCM#19
bors[bot] merged 9 commits into
rust-num:masterfrom
strake:gcd

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@strake

@strakestrake commented Dec 18, 2018•
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@strake
strakeforce-pushed the gcd branch 5 times, most recently from 6accdbc to f6f06f8CompareDecember 19, 2018 05:43
@strake

strake commented Mar 21, 2019

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Rebased, PTAL

cuviper
cuviper requested changes Mar 29, 2019
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Please cargo fmt this, and if it skips the macro impls, please format them manually.

cc #10 and #12 that overlap this PR.

Comment threadsrc/lib.rs Outdated
#[cfg_attr(array_clone, derive(Clone))]
pub struct ExtendedGcd<A> {
pub gcd: A,
pub coeffs: [A; 2],

@cuvipercuviperMar 29, 2019

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Let's use separate x and y, so we can document it something like this:

Bézout's identity — Let a and b be integers with greatest common divisor d. Then, there exist integers x and y such that ax + by = d.

Then we also don't have to worry about array_clone.

Comment threadsrc/lib.rs Outdated
let q = r.1.clone() / r.0.clone();
let f = |r: &mut (Self, Self)| {
mem::swap(&mut r.0, &mut r.1);
r.0 -= q.clone() * r.1.clone();

@cuvipercuviperMar 29, 2019

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Hmm, it's a little annoying to have SubAssign in the API just for this, and AFAICT it's only needed because you're working through &mut. If the closure used values instead, or if you just flattened these three calls, then you could move and then reassign r.0 just fine.

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Maybe we should require Signed though -- I believe it's useless for unsigned integers, since one of the coefficients must be negative, except the degenerate case with zeros.

@strake

strake commented Apr 10, 2019

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@cuviper All done, PTAL

@cuviper

cuviper commented Apr 25, 2019

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Thanks!

bors r+

borsBot added a commit that referenced this pull request Apr 25, 2019
@bors@strake@cuviper
Merge#19
fc93e11
19: Define extended GCD, combined GCD+LCM r=cuviper a=strake
Co-authored-by: M Farkas-Dyck <strake888@gmail.com>
Co-authored-by: Josh Stone <cuviper@gmail.com>
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borsBot commented Apr 25, 2019

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Build failed

@cuviper

cuviper commented Apr 25, 2019

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Sorry, that was my fault.

bors r+

borsBot added a commit that referenced this pull request Apr 25, 2019
@bors@strake@cuviper
Merge#19
4271330
19: Define extended GCD, combined GCD+LCM r=cuviper a=strake
Co-authored-by: M Farkas-Dyck <strake888@gmail.com>
Co-authored-by: Josh Stone <cuviper@gmail.com>
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Build succeeded

@bors
borsBot merged commit a169ee2 into rust-num:masterApr 25, 2019
@cuvipercuviper mentioned this pull request May 20, 2019
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@cuvipercuviper mentioned this pull request Dec 22, 2020
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@strake@cuviper@error256