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Remove AVX2 addition formulas

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Only the readdition formulas are actually used by scalar multiplication, so
there's no reason to implement vectorized addition.
This commit is contained in:
Henry de Valence 2018-03-26 17:12:32 -07:00
parent c73a0fd0d6
commit e8b053b281
1 changed files with 2 additions and 108 deletions
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110
src/backend/avx2/edwards.rs
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@ -132,17 +132,6 @@ impl<'a> Neg for &'a CachedPoint {
} }
} }
impl<'a> Neg for &'a ExtendedPoint {
type Output = ExtendedPoint;
fn neg(self) -> ExtendedPoint {
let mut neg = *self;
// (X Y Z T) -> (-X Y Z -T)
neg.0.negate(A_LANES | D_LANES);
neg
}
}
impl ExtendedPoint { impl ExtendedPoint {
pub fn double(&self) -> ExtendedPoint { pub fn double(&self) -> ExtendedPoint {
unsafe { unsafe {
@ -287,80 +276,6 @@ impl<'a, 'b> Add<&'b CachedPoint> for &'a ExtendedPoint {
} }
} }
impl<'a, 'b> Add<&'b ExtendedPoint> for &'a ExtendedPoint {
type Output = ExtendedPoint;
/// Uses a slight tweak of the parallel unified formulas of HWCD'08
fn add(self, other: &'b ExtendedPoint) -> ExtendedPoint {
unsafe {
use stdsimd::vendor::_mm256_permute2x128_si256;
use stdsimd::vendor::_mm256_permutevar8x32_epi32;
use stdsimd::vendor::_mm256_blend_epi32;
let P: &FieldElement32x4 = &self.0;
let Q: &FieldElement32x4 = &other.0;
let mut t0 = FieldElement32x4::zero();
let mut t1 = FieldElement32x4::zero();
// set t0 = (X1 Y1 X2 Y2)
for i in 0..5 {
t0.0[i] = _mm256_permute2x128_si256(P.0[i].into(), Q.0[i].into(), 32).into();
}
// set t0 = (Y1-X1 Y1+X1 Y2-X2 Y2+X2) = (S0 S1 S2 S3)
t0.diff_sum(0xff);
// set t1 = (S0 S1 Z1 T1)
// set t0 = (S2 S3 Z2 T2)
for i in 0..5 {
// why does this intrinsic take an i32 for the imm8 ???
t1.0[i] = _mm256_blend_epi32(t0.0[i].into(), P.0[i].into(), (C_LANES | D_LANES) as i32).into();
t0.0[i] = _mm256_permute2x128_si256(t0.0[i].into(), Q.0[i].into(), 49).into();
}
// set t2 = (S0*S2 S1*S3 Z1*Z2 T1*T2) = (S4 S5 S6 S7)
let mut t2 = &t0 * &t1;
//// set t2 = (S8 S9 S10 S11)
// set t2 = (121666*S4 121666*S5 2*121666*S6 2*121665*S7)
// = ( S8 S9 S10 -S11)
t2.scale_by_curve_constants();
// set t2 = (S8 S9 -S11 S10)
t2.swap_CD();
// set t2 = (S9-S8 S9+S8 S10+S11 S10-S11) = (S12 S13 S15 S14)
t2.diff_sum(0xff);
let c0 = u32x8::new(0,4,2,6,4,0,6,2); // (ABCD) -> (ACCA)
let c1 = u32x8::new(5,1,7,3,5,1,7,3); // (ABCD) -> (DBDB)
// set t0 = (S12 S15 S15 S12)
// set t1 = (S14 S13 S14 S13)
for i in 0..5 {
t0.0[i] = _mm256_permutevar8x32_epi32(t2.0[i], c0);
t1.0[i] = _mm256_permutevar8x32_epi32(t2.0[i], c1);
}
// return (S12*S14 S15*S13 S15*S14 S12*S13) = (X3 Y3 Z3 T3)
ExtendedPoint(&t0 * &t1)
}
}
}
impl<'a, 'b> Sub<&'b ExtendedPoint> for &'a ExtendedPoint {
type Output = ExtendedPoint;
/// Implement subtraction by negating the point and adding.
///
/// Empirically, this seems about the same cost as a custom subtraction impl (maybe because the
/// benefit is cancelled by increased code size?)
fn sub(self, other: &'b ExtendedPoint) -> ExtendedPoint {
self + &(-other)
}
}
impl<'a, 'b> Sub<&'b CachedPoint> for &'a ExtendedPoint { impl<'a, 'b> Sub<&'b CachedPoint> for &'a ExtendedPoint {
type Output = ExtendedPoint; type Output = ExtendedPoint;
@ -466,14 +381,11 @@ mod test {
fn addition_test_helper(P: edwards::EdwardsPoint, Q: edwards::EdwardsPoint) { fn addition_test_helper(P: edwards::EdwardsPoint, Q: edwards::EdwardsPoint) {
// Test the serial implementation of the parallel addition formulas // Test the serial implementation of the parallel addition formulas
let R_serial: edwards::EdwardsPoint = serial_add(P.into(), Q.into()).into(); let R_serial: edwards::EdwardsPoint = serial_add(P.into(), Q.into()).into();
// Test the vector implementation of the parallel addition formulas
let R_vector: edwards::EdwardsPoint = (&ExtendedPoint::from(P) + &ExtendedPoint::from(Q)).into();
// Test the vector implementation of the parallel subtraction formulas
let S_vector: edwards::EdwardsPoint = (&ExtendedPoint::from(P) - &ExtendedPoint::from(Q)).into();
// Test the vector implementation of the parallel readdition formulas // Test the vector implementation of the parallel readdition formulas
let cached_Q = CachedPoint::from(ExtendedPoint::from(Q)); let cached_Q = CachedPoint::from(ExtendedPoint::from(Q));
let T_vector: edwards::EdwardsPoint = (&ExtendedPoint::from(P) + &cached_Q).into(); let R_vector: edwards::EdwardsPoint = (&ExtendedPoint::from(P) + &cached_Q).into();
let S_vector: edwards::EdwardsPoint = (&ExtendedPoint::from(P) - &cached_Q).into();
println!("Testing point addition:"); println!("Testing point addition:");
println!("P = {:?}", P); println!("P = {:?}", P);
@ -482,32 +394,14 @@ mod test {
println!("R = P + Q = {:?}", &P + &Q); println!("R = P + Q = {:?}", &P + &Q);
println!("R_serial = {:?}", R_serial); println!("R_serial = {:?}", R_serial);
println!("R_vector = {:?}", R_vector); println!("R_vector = {:?}", R_vector);
println!("T_vector = {:?}", T_vector);
println!("S = P - Q = {:?}", &P - &Q); println!("S = P - Q = {:?}", &P - &Q);
println!("S_vector = {:?}", S_vector); println!("S_vector = {:?}", S_vector);
assert_eq!(R_serial.compress(), (&P + &Q).compress()); assert_eq!(R_serial.compress(), (&P + &Q).compress());
assert_eq!(R_vector.compress(), (&P + &Q).compress()); assert_eq!(R_vector.compress(), (&P + &Q).compress());
assert_eq!(T_vector.compress(), (&P + &Q).compress());
assert_eq!(S_vector.compress(), (&P - &Q).compress()); assert_eq!(S_vector.compress(), (&P - &Q).compress());
println!("OK!\n"); println!("OK!\n");
} }
#[test]
fn sub_vs_add_minus() {
let P: ExtendedPoint = edwards::EdwardsPoint::identity().into();
let Q: ExtendedPoint = edwards::EdwardsPoint::identity().into();
let mQ = -&Q;
println!("sub");
let R1: edwards::EdwardsPoint = (&P - &Q).into();
println!("add neg");
let R2: edwards::EdwardsPoint = (&P + &mQ).into();
assert_eq!(R2.compress(), edwards::EdwardsPoint::identity().compress());
assert_eq!(R1.compress(), edwards::EdwardsPoint::identity().compress());
}
#[test] #[test]
fn vector_addition_vs_serial_addition_vs_edwards_extendedpoint() { fn vector_addition_vs_serial_addition_vs_edwards_extendedpoint() {
use constants; use constants;