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Merge pull request #130 from mir-protocol/exp_gate_nits

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nits
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Nicholas Ward 2021-07-27 12:59:14 -07:00 committed by GitHub
commit 9f4cf9f3d9
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1 changed files with 9 additions and 8 deletions
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17
src/gates/exponentiation.rs
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@ -38,6 +38,7 @@ impl<F: Extendable<D>, const D: usize> ExponentiationGate<F, D> {
1 1
} }
/// The `i`th bit of the exponent, in little-endian order.
pub fn wires_power_bit(&self, i: usize) -> usize { pub fn wires_power_bit(&self, i: usize) -> usize {
debug_assert!(i < self.num_power_bits); debug_assert!(i < self.num_power_bits);
2 + i 2 + i
@ -68,21 +69,22 @@ impl<F: Extendable<D>, const D: usize> Gate<F, D> for ExponentiationGate<F, D> {
let mut constraints = Vec::new(); let mut constraints = Vec::new();
let power_bits_reversed = &power_bits.iter().cloned().rev().collect::<Vec<_>>()[..]; let computed_power = reduce_with_powers(&power_bits, F::Extension::TWO);
let computed_power = reduce_with_powers(power_bits_reversed, F::Extension::TWO);
constraints.push(power - computed_power); constraints.push(power - computed_power);
for i in 0..self.num_power_bits { for i in 0..self.num_power_bits {
let current_intermediate_value = if i == 0 { let prev_intermediate_value = if i == 0 {
F::Extension::ONE F::Extension::ONE
} else { } else {
intermediate_values[i - 1] * intermediate_values[i - 1] intermediate_values[i - 1].square()
}; };
let cur_bit = power_bits[i]; // power_bits is in LE order, but we accumulate in BE order.
let cur_bit = power_bits[self.num_power_bits - i - 1];
let not_cur_bit = F::Extension::ONE - cur_bit; let not_cur_bit = F::Extension::ONE - cur_bit;
let computed_intermediate_value = let computed_intermediate_value =
current_intermediate_value * (cur_bit * base + not_cur_bit); prev_intermediate_value * (cur_bit * base + not_cur_bit);
constraints.push(computed_intermediate_value - intermediate_values[i]); constraints.push(computed_intermediate_value - intermediate_values[i]);
} }
@ -136,7 +138,7 @@ impl<F: Extendable<D>, const D: usize> SimpleGenerator<F> for ExponentiationGene
fn dependencies(&self) -> Vec<Target> { fn dependencies(&self) -> Vec<Target> {
let local_target = |input| Target::wire(self.gate_index, input); let local_target = |input| Target::wire(self.gate_index, input);
let mut deps = Vec::new(); let mut deps = Vec::with_capacity(self.gate.num_power_bits + 2);
deps.push(local_target(self.gate.wires_base())); deps.push(local_target(self.gate.wires_base()));
deps.push(local_target(self.gate.wires_power())); deps.push(local_target(self.gate.wires_power()));
for i in 0..self.gate.num_power_bits { for i in 0..self.gate.num_power_bits {
@ -230,7 +232,6 @@ mod tests {
power_bits.push(cur_power % 2); power_bits.push(cur_power % 2);
cur_power /= 2; cur_power /= 2;
} }
power_bits = power_bits.iter().cloned().rev().collect::<Vec<_>>();
let num_power_bits = power_bits.len(); let num_power_bits = power_bits.len();