mirror of
https://github.com/logos-storage/plonky2.git
synced 2026-01-09 17:23:08 +00:00
100 lines
3.6 KiB
Rust
100 lines
3.6 KiB
Rust
use crate::circuit_builder::CircuitBuilder;
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use crate::field::extension_field::Extendable;
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use crate::field::field::Field;
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use crate::gates::base_sum::{BaseSplitGenerator, BaseSumGate};
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use crate::generator::{SimpleGenerator, WitnessGenerator};
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use crate::target::Target;
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use crate::util::{ceil_div_usize, log2_strict};
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use crate::wire::Wire;
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use crate::witness::PartialWitness;
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impl<F: Extendable<D>, const D: usize> CircuitBuilder<F, D> {
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/// Split the given element into a list of targets, where each one represents a
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/// base-B limb of the element, with little-endian ordering.
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pub(crate) fn split_le_base<const B: usize>(
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&mut self,
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x: Target,
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num_limbs: usize,
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) -> Vec<Target> {
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let gate = self.add_gate(BaseSumGate::<B>::new(num_limbs), vec![]);
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let sum = Target::wire(gate, BaseSumGate::<B>::WIRE_SUM);
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self.route(x, sum);
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Target::wires_from_range(
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gate,
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BaseSumGate::<B>::WIRE_LIMBS_START..BaseSumGate::<B>::WIRE_LIMBS_START + num_limbs,
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)
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}
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/// Asserts that `x`'s bit representation has at least `trailing_zeros` trailing zeros.
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pub(crate) fn assert_trailing_zeros<const B: usize>(&mut self, x: Target, trailing_zeros: u32) {
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let num_limbs = num_limbs(64, B);
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let num_limbs_to_check = num_limbs_to_check(trailing_zeros, B);
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let limbs = self.split_le_base::<B>(x, num_limbs);
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assert!(
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num_limbs_to_check < self.config.num_routed_wires,
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"Not enough routed wires."
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);
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for i in 0..num_limbs_to_check {
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self.assert_zero(limbs[i]);
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}
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}
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pub(crate) fn reverse_bits<const B: usize>(&mut self, x: Target, num_limbs: usize) -> Target {
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let gate = self.add_gate(BaseSumGate::<B>::new(num_limbs), vec![]);
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let sum = Target::wire(gate, BaseSumGate::<B>::WIRE_SUM);
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self.route(x, sum);
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Target::wire(gate, BaseSumGate::<B>::WIRE_REVERSED_SUM)
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}
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}
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/// Returns `k` such that any number with `k` trailing zeros in base `base` has at least
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/// `n` trailing zeros in base 2.
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#[allow(unconditional_panic)]
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const fn num_limbs_to_check(n: u32, base: usize) -> usize {
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if base % 2 == 1 {
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// Dirty trick to panic if the base is odd.
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// TODO: replace with `assert_eq!(base % 2, 0, "Base should be even.")` when stable.
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[][0]
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} else {
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ceil_div_usize(n as usize, base.trailing_zeros() as usize)
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}
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}
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fn num_limbs(n_log: u32, base: usize) -> usize {
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((n_log as f64) * 2.0_f64.log(base as f64)).ceil() as usize
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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use crate::circuit_data::CircuitConfig;
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use crate::field::crandall_field::CrandallField;
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#[test]
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fn test_split_base() {
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type F = CrandallField;
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let config = CircuitConfig::large_config();
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let mut builder = CircuitBuilder::<F, 4>::new(config);
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let x = F::from_canonical_usize(0b110100000); // 416 = 1532 in base 6.
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let xt = builder.constant(x);
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let limbs = builder.split_le_base::<6>(xt, 24);
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let one = builder.one();
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let two = builder.two();
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let three = builder.constant(F::from_canonical_u64(3));
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let five = builder.constant(F::from_canonical_u64(5));
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builder.assert_equal(limbs[0], two);
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builder.assert_equal(limbs[1], three);
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builder.assert_equal(limbs[2], five);
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builder.assert_equal(limbs[3], one);
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builder.assert_trailing_zeros::<6>(xt, 4);
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builder.assert_trailing_zeros::<4>(xt, 5);
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builder.assert_trailing_zeros::<12>(xt, 5);
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let data = builder.build();
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let proof = data.prove(PartialWitness::new());
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}
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}
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