Add a special case for single-digit divisors #42
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It was pointed out in the blog post [Big Integers in Zig] that we don't
have a special case in `num-bigint` for single-digit divisors. While
you can already get this optimization by dividing directly by `u32`,
it's easy to make small `BigUint` divisors work like this too.
$ cargo benchcmp baseline single-div
name baseline ns/iter single-div ns/iter diff ns/iter diff % speedup
factorial_div_biguint 5,638,353 1,005,488 -4,632,865 -82.17% x 5.61
`BigInt` will also gain from this, since it uses `BigUint` division
internally.
Running [zig-bn's facdiv-rs] shows a nice improvement too. My i7-7700K
with Rust 1.26 goes from 4.15 seconds to just 0.65 -- a 6.38x speedup!
[Big Integers in Zig]: https://tiehuis.github.io/big-integers-in-zig#division-test-single-limb
[zig-bn's facdiv-rs]: https://github.com/tiehuis/zig-bn/tree/master/bench/facdiv/crate-facdiv-rs
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42: Add a special case for single-digit divisors r=cuviper a=cuviper
It was pointed out in the blog post [Big Integers in Zig] that we don't
have a special case in `num-bigint` for single-digit divisors. While
you can already get this optimization by dividing directly by `u32`,
it's easy to make small `BigUint` divisors work like this too.
$ cargo benchcmp baseline single-div
name baseline ns/iter single-div ns/iter diff ns/iter diff % speedup
factorial_div_biguint 5,638,353 1,005,488 -4,632,865 -82.17% x 5.61
`BigInt` will also gain from this, since it uses `BigUint` division
internally.
Running [zig-bn's facdiv-rs] shows a nice improvement too. My i7-7700K
with Rust 1.26 goes from 4.15 seconds to just 0.65 -- a 6.38x speedup!
[Big Integers in Zig]: https://tiehuis.github.io/big-integers-in-zig#division-test-single-limb
[zig-bn's facdiv-rs]: https://github.com/tiehuis/zig-bn/tree/master/bench/facdiv/crate-facdiv-rs
Co-authored-by: Josh Stone <cuviper@gmail.com>
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It was pointed out in the blog post Big Integers in Zig that we don't
have a special case in
num-bigintfor single-digit divisors. Whileyou can already get this optimization by dividing directly by
u32,it's easy to make small
BigUintdivisors work like this too.BigIntwill also gain from this, since it usesBigUintdivisioninternally.
Running zig-bn's facdiv-rs shows a nice improvement too. My i7-7700K
with Rust 1.26 goes from 4.15 seconds to just 0.65 -- a 6.38x speedup!