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Optimize some exp methods to use ExponentiationGate (#151)

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Daniel Lubarov 2021-08-04 09:55:29 -07:00 committed by GitHub
parent 8b8e4d223d
commit 079baff718
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1 changed files with 14 additions and 13 deletions
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27
src/gadgets/arithmetic.rs
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@ -4,7 +4,6 @@ use crate::field::extension_field::Extendable;
use crate::gates::exponentiation::ExponentiationGate;
use crate::iop::target::Target;
use crate::plonk::circuit_builder::CircuitBuilder;
use crate::util::log2_ceil;
impl<F: Extendable<D>, const D: usize> CircuitBuilder<F, D> {
/// Computes `-x`.
@ -97,12 +96,8 @@ impl<F: Extendable<D>, const D: usize> CircuitBuilder<F, D> {
}
/// Exponentiate `base` to the power of `2^power_log`.
// TODO: Test
pub fn exp_power_of_2(&mut self, mut base: Target, power_log: usize) -> Target {
for _ in 0..power_log {
base = self.square(base);
}
base
pub fn exp_power_of_2(&mut self, base: Target, power_log: usize) -> Target {
self.exp_u64(base, 1 << power_log)
}
// TODO: Test
@ -110,12 +105,12 @@ impl<F: Extendable<D>, const D: usize> CircuitBuilder<F, D> {
pub fn exp_from_bits(
&mut self,
base: Target,
exponent_bits: impl Iterator<Item = impl Borrow<Target>>,
exponent_bits: impl IntoIterator<Item = impl Borrow<Target>>,
) -> Target {
let zero = self.zero();
let gate = ExponentiationGate::new(self.config.clone());
let num_power_bits = gate.num_power_bits;
let mut exp_bits_vec: Vec<Target> = exponent_bits.map(|b| *b.borrow()).collect();
let mut exp_bits_vec: Vec<Target> = exponent_bits.into_iter().map(|b| *b.borrow()).collect();
while exp_bits_vec.len() < num_power_bits {
exp_bits_vec.push(zero);
}
@ -139,10 +134,16 @@ impl<F: Extendable<D>, const D: usize> CircuitBuilder<F, D> {
/// Exponentiate `base` to the power of a known `exponent`.
// TODO: Test
pub fn exp_u64(&mut self, base: Target, exponent: u64) -> Target {
let exp_target = self.constant(F::from_canonical_u64(exponent));
let num_bits = log2_ceil(exponent as usize + 1);
self.exp(base, exp_target, num_bits)
pub fn exp_u64(&mut self, base: Target, mut exponent: u64) -> Target {
let mut exp_bits = Vec::new();
while exponent != 0 {
let bit = exponent & 1;
let bit_target = self.constant(F::from_canonical_u64(bit));
exp_bits.push(bit_target);
exponent >>= 1;
}
self.exp_from_bits(base, exp_bits)
}
/// Computes `x / y`. Results in an unsatisfiable instance if `y = 0`.