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factor::miller_rabin: Hoist edge-cases (even, <2) out of test()

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test() takes a modulus that is known to not be even or <2 (otherwise the
Montgomery value could not be constructed), so those checks can be hoisted
into is_prime() and out of the critical path.
This commit is contained in:
nicoo 2020-07-04 20:52:32 +02:00
parent 4f08e28167
commit 9b149a759b
1 changed files with 5 additions and 7 deletions
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12
src/uu/factor/src/miller_rabin.rs
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@ -44,12 +44,8 @@ pub(crate) fn test<A: Arithmetic + Basis>(m: A) -> Result {
use self::Result::*;
let n = m.modulus();
if n < 2 {
return Pseudoprime;
}
if n % 2 == 0 {
return if n == 2 { Prime } else { Composite(2) };
}
debug_assert!(n > 1);
debug_assert!(n % 2 != 0);
// n-1 = r 2ⁱ
let i = (n - 1).trailing_zeros();
@ -104,7 +100,9 @@ pub(crate) fn test<A: Arithmetic + Basis>(m: A) -> Result {
// Used by build.rs' tests and debug assertions
#[allow(dead_code)]
pub(crate) fn is_prime(n: u64) -> bool {
if n % 2 == 0 {
if n < 2 {
false
} else if n % 2 == 0 {
n == 2
} else {
test::<Montgomery<u64>>(Montgomery::new(n)).is_prime()