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Remove large temprary stack allocations from SqrtTables::new

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This commit is contained in:
Jack Grigg 2021-04-28 14:21:45 +12:00
parent 376ba4eeca
commit ccbfaf6a20
1 changed files with 24 additions and 19 deletions
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43
src/arithmetic/fields.rs
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@ -199,37 +199,42 @@ impl<F: FieldExt> SqrtTables<F> {
marker: PhantomData,
};
let gtab: Vec<Vec<F>> = (0..4)
.scan(F::ROOT_OF_UNITY, |gi, _| {
// gi == ROOT_OF_UNITY^(256^i)
let gtab_i: Vec<F> = (0..256)
.scan(F::one(), |acc, _| {
let res = *acc;
*acc *= *gi;
Some(res)
})
.collect();
*gi = gtab_i[255] * *gi;
Some(gtab_i)
})
.collect();
let mut gtab = (0..4).scan(F::ROOT_OF_UNITY, |gi, _| {
// gi == ROOT_OF_UNITY^(256^i)
let gtab_i: Vec<F> = (0..256)
.scan(F::one(), |acc, _| {
let res = *acc;
*acc *= *gi;
Some(res)
})
.collect();
*gi = gtab_i[255] * *gi;
Some(gtab_i)
});
let gtab_0 = gtab.next().unwrap();
let gtab_1 = gtab.next().unwrap();
let gtab_2 = gtab.next().unwrap();
let mut gtab_3 = gtab.next().unwrap();
assert_eq!(gtab.next(), None);
// Now invert gtab[3].
let mut inv: Vec<u8> = vec![1; hash_mod];
for j in 0..256 {
let hash = hasher.hash(&gtab[3][j]);
let hash = hasher.hash(&gtab_3[j]);
// 1 is the last value to be assigned, so this ensures there are no collisions.
assert!(inv[hash] == 1);
inv[hash] = ((256 - j) & 0xFF) as u8;
}
gtab_3.truncate(129);
SqrtTables::<F> {
hasher,
inv,
g0: Box::new(gtab[0][..].try_into().unwrap()),
g1: Box::new(gtab[1][..].try_into().unwrap()),
g2: Box::new(gtab[2][..].try_into().unwrap()),
g3: Box::new(gtab[3][0..129].try_into().unwrap()),
g0: gtab_0.into_boxed_slice().try_into().unwrap(),
g1: gtab_1.into_boxed_slice().try_into().unwrap(),
g2: gtab_2.into_boxed_slice().try_into().unwrap(),
g3: gtab_3.into_boxed_slice().try_into().unwrap(),
}
}