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exponentiation gadget

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This commit is contained in:
Nicholas Ward 2021-07-28 10:56:12 -07:00
parent 6749a94c52
commit 247fa39386
1 changed files with 33 additions and 3 deletions
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36
src/gadgets/arithmetic.rs
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@ -2,6 +2,7 @@ use std::borrow::Borrow;
use crate::circuit_builder::CircuitBuilder;
use crate::field::extension_field::Extendable;
use crate::gates::exponentiation::ExponentiationGate;
use crate::target::Target;
impl<F: Extendable<D>, const D: usize> CircuitBuilder<F, D> {
@ -193,14 +194,43 @@ impl<F: Extendable<D>, const D: usize> CircuitBuilder<F, D> {
/// Exponentiate `base` to the power of `exponent`, where `exponent < 2^num_bits`.
pub fn exp(&mut self, base: Target, exponent: Target, num_bits: usize) -> Target {
let exponent_bits = self.split_le(exponent, num_bits);
self.exp_from_bits(base, exponent_bits.iter())
let gate = ExponentiationGate::new(exponent_bits.len());
let gate_index = self.add_gate(gate.clone(), vec![]);
self.route(exponent, Target::wire(gate_index, gate.wire_power()));
exponent_bits.iter().enumerate().for_each(|(i, &bit)| {
self.route(bit, Target::wire(gate_index, gate.wire_power_bit(i)));
});
Target::wire(gate_index, gate.wire_output())
}
/// Exponentiate `base` to the power of a known `exponent`.
// TODO: Test
pub fn exp_u64(&mut self, base: Target, exponent: u64) -> Target {
let base_ext = self.convert_to_ext(base);
self.exp_u64_extension(base_ext, exponent).0[0]
let mut exp_bits = Vec::new();
let mut cur_exp = exponent;
while cur_exp > 0 {
exp_bits.push(cur_exp % 2);
cur_exp /= 2;
}
let exp_target = self.constant(F::from_canonical_u64(exponent));
let exp_bits_targets: Vec<_> = exp_bits
.iter()
.map(|b| self.constant(F::from_canonical_u64(*b)))
.collect();
let gate = ExponentiationGate::new(exp_bits.len());
let gate_index = self.add_gate(gate.clone(), vec![]);
self.route(exp_target, Target::wire(gate_index, gate.wire_power()));
exp_bits_targets.iter().enumerate().for_each(|(i, &bit)| {
self.route(bit, Target::wire(gate_index, gate.wire_power_bit(i)));
});
Target::wire(gate_index, gate.wire_output())
}
/// Computes `x / y`. Results in an unsatisfiable instance if `y = 0`.