mirror of https://github.com/gtank/ristretto255
ristretto255: fix Encode
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50d9eb21ae
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1849461667
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@ -148,24 +148,24 @@ func (e *Element) Encode(b []byte) []byte {
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// Ignore was_square since this is always square
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// (_, invsqrt) = SQRT_RATIO_M1(1, u1 * u2^2)
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invSqrt := &radix51.FieldElement{}
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_ = feSqrtRatio(invSqrt, u1, tmp.Square(u2))
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feSqrtRatio(invSqrt, radix51.One, tmp.Square(u2).Mul(tmp, u1))
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// den1 = invsqrt * u1
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// den2 = invsqrt * u2
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// z_inv = den1 * den2 * t0
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den1, den2 := &radix51.FieldElement{}, &radix51.FieldElement{}
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zInv := &radix51.FieldElement{}
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den1.Mul(invSqrt, u1)
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den2.Mul(invSqrt, u2)
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// z_inv = den1 * den2 * t0
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zInv := &radix51.FieldElement{}
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zInv.Mul(den1, den2).Mul(zInv, &e.r.T)
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// ix0 = x0 * SQRT_M1
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// iy0 = y0 * SQRT_M1
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// enchanted_denominator = den1 * INVSQRT_A_MINUS_D
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ix0, iy0 := &radix51.FieldElement{}, &radix51.FieldElement{}
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enchantedDenominator := &radix51.FieldElement{}
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ix0.Mul(&e.r.X, sqrtM1)
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iy0.Mul(&e.r.Y, sqrtM1)
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// enchanted_denominator = den1 * INVSQRT_A_MINUS_D
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enchantedDenominator := &radix51.FieldElement{}
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enchantedDenominator.Mul(den1, invSqrtAMinusD)
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// rotate = IS_NEGATIVE(t0 * z_inv)
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@ -173,20 +173,20 @@ func (e *Element) Encode(b []byte) []byte {
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// x = CT_SELECT(iy0 IF rotate ELSE x0)
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// y = CT_SELECT(ix0 IF rotate ELSE y0)
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// z = z0
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// den_inv = CT_SELECT(enchanted_denominator IF rotate ELSE den2)
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x, y := &radix51.FieldElement{}, &radix51.FieldElement{}
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denInv := &radix51.FieldElement{}
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x.Select(iy0, &e.r.X, rotate)
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y.Select(ix0, &e.r.Y, rotate)
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// z = z0
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z := &e.r.Z
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// den_inv = CT_SELECT(enchanted_denominator IF rotate ELSE den2)
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denInv := &radix51.FieldElement{}
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denInv.Select(enchantedDenominator, den2, rotate)
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// y = CT_NEG(y, IS_NEGATIVE(x * z_inv))
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y.CondNeg(y, tmp.Mul(x, zInv).IsNegative())
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// s = CT_ABS(den_inv * (z - y))
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s := tmp.Mul(denInv, tmp.Sub(z, y)).Abs(tmp)
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s := tmp.Sub(z, y).Mul(tmp, denInv).Abs(tmp)
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// Return the canonical little-endian encoding of s.
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return s.Bytes(b)
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