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Fix sign error

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Henry de Valence 2017-02-21 11:39:07 -08:00
parent 6b3dbf6870
commit 5daa217b18
1 changed files with 3 additions and 6 deletions
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9
src/decaf.rs
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@ -159,15 +159,12 @@ impl DecafPoint {
r.conditional_negate(m2uZ.is_negative_decaf()); r.conditional_negate(m2uZ.is_negative_decaf());
// Step 4: Compute s = | u(r(aZX - dYT)+Y)/a| // Step 4: Compute s = | u(r(aZX - dYT)+Y)/a|
// = |-u(r(aZX - dYT)+Y)| // = |u(r(-ZX - dYT)+Y)| since a = -1
let minus_ZX = -&(&self.0.Z * &X); let minus_ZX = -&(&self.0.Z * &X);
let dYT = &constants::d * &(&Y * &T); let dYT = &constants::d * &(&Y * &T);
// Compute s = u(r(aZX - dYT)+Y) // Compute s = u(r(aZX - dYT)+Y) and cnegate for abs
let mut s = &u * &(&(&r * &(&minus_ZX - &dYT)) + &Y); let mut s = &u * &(&(&r * &(&minus_ZX - &dYT)) + &Y);
// Set s <- |-s| let neg = s.is_negative_decaf();
// XXX I think there's a sign error somewhere?
// flipping the sign here makes the tests pass
let neg = s.is_nonnegative_decaf();
s.conditional_negate(neg); s.conditional_negate(neg);
CompressedDecaf(s.to_bytes()) CompressedDecaf(s.to_bytes())
} }