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Try to connect the AVX2 backend to the ExtendedPoint frontend

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Henry de Valence 2017-11-20 15:27:44 -08:00
parent 77766b3422
commit 97fe2f0bf4
3 changed files with 40 additions and 29 deletions
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1
build.rs
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@ -1,4 +1,5 @@
#![cfg_attr(feature = "nightly", feature(i128_type))]
#![cfg_attr(feature = "nightly", feature(cfg_target_feature))]
#![allow(unused_variables)]
#![allow(non_snake_case)]
#![allow(dead_code)]

65
src/edwards.rs
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@ -432,38 +432,47 @@ impl<'a, 'b> Mul<&'b Scalar> for &'a ExtendedPoint {
/// For scalar multiplication of a basepoint,
/// `EdwardsBasepointTable` is approximately 4x faster.
fn mul(self, scalar: &'b Scalar) -> ExtendedPoint {
// Construct a lookup table of [P,2P,3P,4P,5P,6P,7P,8P]
let P = self.to_projective_niels();
let mut lookup_table: [ProjectiveNielsPoint; 8] = [P; 8];
for i in 0..7 {
lookup_table[i+1] = (self + &lookup_table[i])
.to_extended().to_projective_niels();
// If we built with AVX2, use the AVX2 backend.
#[cfg(all(target_feature = "avx2", feature = "avx2_backend"))] {
use backend::avx2::edwards as edwards_avx2;
let P_avx2 = edwards_avx2::ExtendedPoint::from(*self);
return ExtendedPoint::from(&P_avx2 * scalar);
}
// Otherwise, proceed as normal:
#[cfg(not(all(target_feature = "avx2", feature = "avx2_backend")))] {
// Construct a lookup table of [P,2P,3P,4P,5P,6P,7P,8P]
let P = self.to_projective_niels();
let mut lookup_table: [ProjectiveNielsPoint; 8] = [P; 8];
for i in 0..7 {
lookup_table[i+1] = (self + &lookup_table[i])
.to_extended().to_projective_niels();
}
// Setting s = scalar, compute
//
// s = s_0 + s_1*16^1 + ... + s_63*16^63,
//
// with `-8 ≤ s_i < 8` for `0 ≤ i < 63` and `-8 ≤ s_63 ≤ 8`.
let scalar_digits = scalar.to_radix_16();
// Setting s = scalar, compute
//
// s = s_0 + s_1*16^1 + ... + s_63*16^63,
//
// with `-8 ≤ s_i < 8` for `0 ≤ i < 63` and `-8 ≤ s_63 ≤ 8`.
let scalar_digits = scalar.to_radix_16();
// Compute s*P as
//
// s*P = P*(s_0 + s_1*16^1 + s_2*16^2 + ... + s_63*16^63)
// s*P = P*s_0 + P*s_1*16^1 + P*s_2*16^2 + ... + P*s_63*16^63
// s*P = P*s_0 + 16*(P*s_1 + 16*(P*s_2 + 16*( ... + P*s_63)...))
//
// We sum right-to-left.
let mut Q = ExtendedPoint::identity();
for i in (0..64).rev() {
// Q = 16*Q
Q = Q.mult_by_pow_2(4);
// R = s_i * Q
let R = select_precomputed_point(scalar_digits[i], &lookup_table);
// Q = Q + R
Q = (&Q + &R).to_extended();
// Compute s*P as
//
// s*P = P*(s_0 + s_1*16^1 + s_2*16^2 + ... + s_63*16^63)
// s*P = P*s_0 + P*s_1*16^1 + P*s_2*16^2 + ... + P*s_63*16^63
// s*P = P*s_0 + 16*(P*s_1 + 16*(P*s_2 + 16*( ... + P*s_63)...))
//
// We sum right-to-left.
let mut Q = ExtendedPoint::identity();
for i in (0..64).rev() {
// Q = 16*Q
Q = Q.mult_by_pow_2(4);
// R = s_i * Q
let R = select_precomputed_point(scalar_digits[i], &lookup_table);
// Q = Q + R
Q = (&Q + &R).to_extended();
}
Q
}
Q
}
}

3
src/lib.rs
View file

@ -11,11 +11,12 @@
#![cfg_attr(not(feature = "std"), no_std)]
#![cfg_attr(feature = "alloc", feature(alloc))]
#![cfg_attr(feature = "nightly", feature(i128_type))]
#![cfg_attr(feature = "nightly", feature(cfg_target_feature))]
#![cfg_attr(feature = "bench", feature(test))]
#![cfg_attr(all(feature = "nightly", feature = "std"), feature(zero_one))]
#![allow(unused_features)]
//#![deny(missing_docs)] // refuse to compile if documentation is missing
#![deny(missing_docs)] // refuse to compile if documentation is missing
//! # curve25519-dalek
//!