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mulassign/fallback: make safety invariants explicit

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This simplifies the non-SIMD mulassign, making its safety invariants
explicit and documented.
This commit is contained in:
Luca Bruno 2019-03-30 21:37:54 +00:00 committed by Christopher Berner
parent e61e1eb2d4
commit 09a1db06d9
1 changed files with 8 additions and 6 deletions
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14
src/octets.rs
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@ -6,13 +6,15 @@ use crate::octet::OCTET_MUL_HI_BITS;
use crate::octet::OCTET_MUL_LOW_BITS;
fn mulassign_scalar_fallback(octets: &mut [u8], scalar: &Octet) {
let scalar_index = scalar.byte() as usize;
for i in 0..octets.len() {
unsafe {
*octets.get_unchecked_mut(i) = *OCTET_MUL
let scalar_index = usize::from(scalar.byte());
for item in octets {
let octet_index = usize::from(*item);
// SAFETY: `OCTET_MUL` is a 256x256 matrix, both indexes are `u8` inputs.
*item = unsafe {
*OCTET_MUL
.get_unchecked(scalar_index)
.get_unchecked(*octets.get_unchecked(i) as usize);
}
.get_unchecked(octet_index)
};
}
}