diff --git a/src/circuit/pedersen_hash.rs b/src/circuit/pedersen_hash.rs index 3b0dc45..5aa8562 100644 --- a/src/circuit/pedersen_hash.rs +++ b/src/circuit/pedersen_hash.rs @@ -124,6 +124,94 @@ pub fn pedersen_hash( Ok(edwards_result.unwrap()) } +/// Performs a 3-bit window table lookup. `bits` is in +/// little-endian order. +fn lookup3_xy( + mut cs: CS, + bits: &[Boolean], + coords: &[(E::Fr, E::Fr)] +) -> Result<(AllocatedNum, AllocatedNum), SynthesisError> + where CS: ConstraintSystem +{ + assert_eq!(bits.len(), 3); + assert_eq!(coords.len(), 8); + + // Calculate the index into `coords` + let i = + match (bits[0].get_value(), bits[1].get_value(), bits[2].get_value()) { + (Some(a_value), Some(b_value), Some(c_value)) => { + let mut tmp = 0; + if a_value { + tmp += 1; + } + if b_value { + tmp += 2; + } + if c_value { + tmp += 4; + } + Some(tmp) + }, + _ => None + }; + + // Allocate the x-coordinate resulting from the lookup + let res_x = AllocatedNum::alloc( + cs.namespace(|| "x"), + || { + Ok(coords[*i.get()?].0) + } + )?; + + // Allocate the y-coordinate resulting from the lookup + let res_y = AllocatedNum::alloc( + cs.namespace(|| "y"), + || { + Ok(coords[*i.get()?].1) + } + )?; + + // Compute the coefficients for the lookup constraints + let mut x_coeffs = [E::Fr::zero(); 8]; + let mut y_coeffs = [E::Fr::zero(); 8]; + synth::(3, coords.iter().map(|c| &c.0), &mut x_coeffs); + synth::(3, coords.iter().map(|c| &c.1), &mut y_coeffs); + + let precomp = Boolean::and(cs.namespace(|| "precomp"), &bits[1], &bits[2])?; + + let one = cs.one(); + + cs.enforce( + || "x-coordinate lookup", + LinearCombination::::zero() + (x_coeffs[0b001], one) + + &bits[1].lc::(one, x_coeffs[0b011]) + + &bits[2].lc::(one, x_coeffs[0b101]) + + &precomp.lc::(one, x_coeffs[0b111]), + LinearCombination::::zero() + &bits[0].lc::(one, E::Fr::one()), + LinearCombination::::zero() + res_x.get_variable() + - (x_coeffs[0b000], one) + - &bits[1].lc::(one, x_coeffs[0b010]) + - &bits[2].lc::(one, x_coeffs[0b100]) + - &precomp.lc::(one, x_coeffs[0b110]), + ); + + cs.enforce( + || "y-coordinate lookup", + LinearCombination::::zero() + (y_coeffs[0b001], one) + + &bits[1].lc::(one, y_coeffs[0b011]) + + &bits[2].lc::(one, y_coeffs[0b101]) + + &precomp.lc::(one, y_coeffs[0b111]), + LinearCombination::::zero() + &bits[0].lc::(one, E::Fr::one()), + LinearCombination::::zero() + res_y.get_variable() + - (y_coeffs[0b000], one) + - &bits[1].lc::(one, y_coeffs[0b010]) + - &bits[2].lc::(one, y_coeffs[0b100]) + - &precomp.lc::(one, y_coeffs[0b110]), + ); + + Ok((res_x, res_y)) +} + /// Performs a 3-bit window table lookup, where /// one of the bits is a sign bit. fn lookup3_xy_with_conditional_negation( @@ -270,6 +358,46 @@ mod test { } } + #[test] + fn test_lookup3_xy() { + let mut rng = XorShiftRng::from_seed([0x3dbe6259, 0x8d313d76, 0x3237db17, 0xe5bc0656]); + + for _ in 0..100 { + let mut cs = TestConstraintSystem::::new(); + + let a_val = rng.gen(); + let a = Boolean::from( + AllocatedBit::alloc(cs.namespace(|| "a"), Some(a_val)).unwrap() + ); + + let b_val = rng.gen(); + let b = Boolean::from( + AllocatedBit::alloc(cs.namespace(|| "b"), Some(b_val)).unwrap() + ); + + let c_val = rng.gen(); + let c = Boolean::from( + AllocatedBit::alloc(cs.namespace(|| "c"), Some(c_val)).unwrap() + ); + + let bits = vec![a, b, c]; + + let points: Vec<(Fr, Fr)> = (0..8).map(|_| (rng.gen(), rng.gen())).collect(); + + let res = lookup3_xy(&mut cs, &bits, &points).unwrap(); + + assert!(cs.is_satisfied()); + + let mut index = 0; + if a_val { index += 1 } + if b_val { index += 2 } + if c_val { index += 4 } + + assert_eq!(res.0.get_value().unwrap(), points[index].0); + assert_eq!(res.1.get_value().unwrap(), points[index].1); + } + } + #[test] fn test_lookup3_xy_with_conditional_negation() { let mut rng = XorShiftRng::from_seed([0x3dbe6259, 0x8d313d76, 0x3237db17, 0xe5bc0654]);