mirror of https://github.com/zcash/halo2.git
lookup_range_check.rs: Add short range check lookup.
Also introduce a "strict" mode for the full-length lookup, where "true" requires the field element to be within num_words * K bits, whereas "false" does not.
This commit is contained in:
parent
af335ff7de
commit
3840f280d7
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@ -3,8 +3,8 @@
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use crate::spec::lebs2ip;
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use halo2::{
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circuit::Region,
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plonk::{Advice, Column, ConstraintSystem, Error, Fixed, Permutation},
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circuit::{Layouter, Region},
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plonk::{Advice, Column, ConstraintSystem, Error, Fixed, Permutation, Selector},
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poly::Rotation,
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};
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use std::{convert::TryInto, marker::PhantomData};
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@ -13,19 +13,19 @@ use ff::PrimeFieldBits;
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use super::*;
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#[derive(Debug, Clone)]
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#[derive(Eq, PartialEq, Debug, Clone)]
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pub struct LookupRangeCheckConfig<F: FieldExt + PrimeFieldBits, const K: usize> {
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q_lookup: Column<Fixed>,
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running_sum: Column<Advice>,
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pub q_lookup: Selector,
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pub q_lookup_short: Selector,
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pub short_lookup_bitshift: Column<Fixed>,
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pub running_sum: Column<Advice>,
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constants: Column<Fixed>,
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table_idx: Column<Fixed>,
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perm: Permutation,
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_marker: PhantomData<F>,
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}
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impl<F: FieldExt + PrimeFieldBits, const K: usize> LookupRangeCheckConfig<F, K> {
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/// The `q_lookup` column toggles the lookup on or off. It MUST be assigned
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/// outside of this helper at the appropriate offsets.
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///
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/// The `running_sum` advice column breaks the field element into `K`-bit
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/// words. It is used to construct the input expression to the lookup
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/// argument.
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@ -35,21 +35,28 @@ impl<F: FieldExt + PrimeFieldBits, const K: usize> LookupRangeCheckConfig<F, K>
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/// can be loaded outside this helper.
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pub fn configure(
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meta: &mut ConstraintSystem<F>,
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q_lookup: Column<Fixed>,
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running_sum: Column<Advice>,
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constants: Column<Fixed>,
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table_idx: Column<Fixed>,
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perm: Permutation,
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) -> Self {
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let q_lookup = meta.selector();
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let q_lookup_short = meta.selector();
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let short_lookup_bitshift = meta.fixed_column();
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let config = LookupRangeCheckConfig {
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q_lookup,
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q_lookup_short,
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short_lookup_bitshift,
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running_sum,
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constants,
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table_idx,
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perm,
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_marker: PhantomData,
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};
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// Lookup for range checks K bits and above.
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meta.lookup(|meta| {
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let q_lookup = meta.query_fixed(config.q_lookup, Rotation::cur());
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let q_lookup = meta.query_selector(config.q_lookup);
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let z_cur = meta.query_advice(config.running_sum, Rotation::cur());
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let z_next = meta.query_advice(config.running_sum, Rotation::next());
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// z_i = 2^{K}⋅z_{i + 1} + a_i
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@ -60,6 +67,28 @@ impl<F: FieldExt + PrimeFieldBits, const K: usize> LookupRangeCheckConfig<F, K>
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vec![(q_lookup * word, table)]
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});
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// Lookup for range checks up to S bits, where S < K.
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meta.lookup(|meta| {
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let q_lookup_short = meta.query_selector(config.q_lookup_short);
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let word = meta.query_advice(config.running_sum, Rotation::cur());
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let table = meta.query_fixed(config.table_idx, Rotation::cur());
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vec![(q_lookup_short * word, table)]
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});
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// For short lookups, check that the word has been shifted by the correct number of bits.
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meta.create_gate("Short lookup bitshift", |meta| {
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let inv_two_pow_s = meta.query_fixed(config.short_lookup_bitshift, Rotation::cur());
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let word = meta.query_advice(config.running_sum, Rotation::prev());
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let shifted_word = meta.query_advice(config.running_sum, Rotation::cur());
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let two_pow_k = F::from_u64(1 << K);
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// shifted_word = word * 2^{K-s}
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// = word * 2^K * inv_two_pow_s
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vec![inv_two_pow_s.clone() * (word * two_pow_k * inv_two_pow_s - shifted_word)]
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});
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config
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}
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@ -67,7 +96,7 @@ impl<F: FieldExt + PrimeFieldBits, const K: usize> LookupRangeCheckConfig<F, K>
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// Loads the values [0..2^K) into `table_idx`. This is only used in testing
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// for now, since the Sinsemilla chip provides a pre-loaded table in the
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// Orchard context.
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fn load(&self, layouter: &mut impl Layouter<F>) -> Result<(), Error> {
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pub fn load(&self, layouter: &mut impl Layouter<F>) -> Result<(), Error> {
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layouter.assign_region(
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|| "table_idx",
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|mut gate| {
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@ -85,19 +114,73 @@ impl<F: FieldExt + PrimeFieldBits, const K: usize> LookupRangeCheckConfig<F, K>
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)
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}
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/// Only the lower `num_words * K` bits of the field element are constrained
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/// by this function. If the field element does not fit into this range, then
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/// the final cumulative sum `z_{num_words}` will be nonzero.
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//
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/// It is up to the caller to constrain `z_{num_words}` == 0` outside this
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/// helper, or otherwise constrain upper bits not covered within the
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/// `num_words * K` range.
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pub fn lookup_range_check(
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/// Range check on an existing cell that is copied into this helper.
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pub fn copy_check(
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&self,
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region: &mut Region<'_, F>,
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offset: usize,
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mut layouter: impl Layouter<F>,
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element: CellValue<F>,
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num_words: usize,
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strict: bool,
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) -> Result<Vec<CellValue<F>>, Error> {
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layouter.assign_region(
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|| format!("{:?} words range check", num_words),
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|mut region| {
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// Copy `element` and initialize running sum `z_0 = element` to decompose it.
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let z_0 = copy(
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&mut region,
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|| "z_0",
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self.running_sum,
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0,
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&element,
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&self.perm,
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)?;
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self.range_check(&mut region, z_0, num_words, strict)
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},
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)
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}
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/// Range check on a value that is witnessed in this helper.
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pub fn witness_check(
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&self,
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mut layouter: impl Layouter<F>,
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value: Option<F>,
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num_words: usize,
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strict: bool,
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) -> Result<(CellValue<F>, Vec<CellValue<F>>), Error> {
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layouter.assign_region(
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|| "Witness element",
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|mut region| {
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let z_0 = {
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let cell = region.assign_advice(
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|| "Witness element",
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self.running_sum,
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0,
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|| value.ok_or(Error::SynthesisError),
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)?;
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CellValue::new(cell, value)
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};
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let zs = self.range_check(&mut region, z_0, num_words, strict)?;
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Ok((z_0, zs))
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},
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)
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}
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/// If `strict` is set to "true", the field element must fit into
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/// `num_words * K` bits. In other words, the the final cumulative sum `z_{num_words}`
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/// must be zero.
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///
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/// If `strict` is set to "false", the final `z_{num_words}` is not constrained.
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///
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/// `element` must have been assigned to `self.running_sum` at offset 0.
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fn range_check(
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&self,
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region: &mut Region<'_, F>,
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element: CellValue<F>,
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num_words: usize,
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strict: bool,
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) -> Result<Vec<CellValue<F>>, Error> {
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// `num_words` must fit into a single field element.
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assert!(num_words * K <= F::CAPACITY as usize);
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@ -126,17 +209,7 @@ impl<F: FieldExt + PrimeFieldBits, const K: usize> LookupRangeCheckConfig<F, K>
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}
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};
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// Copy `element` and initialize running sum `z_0 = element` to decompose it.
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let z_0 = copy(
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region,
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|| "z_0",
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self.running_sum,
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offset,
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&element,
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&self.perm,
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)?;
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let mut zs = vec![z_0];
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let mut zs = vec![element];
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// Assign cumulative sum such that
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// z_i = 2^{K}⋅z_{i + 1} + a_i
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@ -144,21 +217,24 @@ impl<F: FieldExt + PrimeFieldBits, const K: usize> LookupRangeCheckConfig<F, K>
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//
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// For `element` = a_0 + 2^10 a_1 + ... + 2^{120} a_{12}}, initialize z_0 = `element`.
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// If `element` fits in 130 bits, we end up with z_{13} = 0.
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let mut z = z_0;
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let mut z = element;
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let inv_two_pow_k = F::from_u64(1u64 << K).invert().unwrap();
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for (idx, word) in words.into_iter().enumerate() {
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for (idx, word) in words.iter().enumerate() {
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// Enable lookup on this row
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self.q_lookup.enable(region, idx)?;
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// z_next = (z_cur - m_cur) / 2^K
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z = {
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let z_val = z
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.value()
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.zip(word)
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.zip(*word)
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.map(|(z, word)| (z - word) * inv_two_pow_k);
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// Assign z_next
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let z_cell = region.assign_advice(
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|| format!("z_{:?}", idx + 1),
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self.running_sum,
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offset + idx + 1,
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idx + 1,
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|| z_val.ok_or(Error::SynthesisError),
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)?;
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@ -167,21 +243,136 @@ impl<F: FieldExt + PrimeFieldBits, const K: usize> LookupRangeCheckConfig<F, K>
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zs.push(z);
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}
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if strict {
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// Constrain the final `z` to be zero.
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let cell =
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region.assign_fixed(|| "zero", self.constants, words.len(), || Ok(F::zero()))?;
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region.constrain_equal(&self.perm, z.cell(), cell)?;
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}
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Ok(zs)
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}
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/// Short range check on an existing cell that is copied into this helper.
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///
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/// # Panics
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///
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/// Panics if NUM_BITS is equal to or larger than K.
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pub fn copy_short_check(
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&self,
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mut layouter: impl Layouter<F>,
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element: CellValue<F>,
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num_bits: usize,
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) -> Result<(), Error> {
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assert!(num_bits < K);
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layouter.assign_region(
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|| format!("Range check {:?} bits", num_bits),
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|mut region| {
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// Copy `element` to use in the k-bit lookup.
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let element = copy(
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&mut region,
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|| "element",
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self.running_sum,
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0,
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&element,
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&self.perm,
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)?;
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self.short_range_check(&mut region, element, num_bits)
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},
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)
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}
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/// Short range check on value that is witnessed in this helper.
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///
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/// # Panics
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///
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/// Panics if num_bits is larger than K.
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pub fn witness_short_check(
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&self,
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mut layouter: impl Layouter<F>,
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element: Option<F>,
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num_bits: usize,
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) -> Result<CellValue<F>, Error> {
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assert!(num_bits <= K);
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layouter.assign_region(
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|| format!("Range check {:?} bits", num_bits),
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|mut region| {
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// Witness `element` to use in the k-bit lookup.
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let element = {
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let cell = region.assign_advice(
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|| "Witness element",
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self.running_sum,
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0,
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|| element.ok_or(Error::SynthesisError),
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)?;
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CellValue::new(cell, element)
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};
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self.short_range_check(&mut region, element, num_bits)?;
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Ok(element)
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},
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)
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}
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/// Constrain `x` to be a NUM_BITS word.
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///
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/// `element` must have been assigned to `self.running_sum` at offset 0.
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fn short_range_check(
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&self,
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region: &mut Region<'_, F>,
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element: CellValue<F>,
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num_bits: usize,
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) -> Result<(), Error> {
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// Enable lookup for `element`, to constrain it to 10 bits.
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self.q_lookup_short.enable(region, 0)?;
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// Assign 2^{-num_bits} in a fixed column.
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{
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// 2^{-num_bits}
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let inv_two_pow_s = F::from_u64(1 << num_bits).invert().unwrap();
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region.assign_fixed(
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|| format!("2^(-{})", num_bits),
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self.short_lookup_bitshift,
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1,
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|| Ok(inv_two_pow_s),
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)?;
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}
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// Assign shifted `element * 2^{K - num_bits}`
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let shifted = element.value().map(|element| {
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let shift = F::from_u64(1 << (K - num_bits));
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element * shift
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});
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print!("element: {:?}", element.value());
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print!("shifted: {:?}", shifted);
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region.assign_advice(
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|| format!("element * 2^({}-{})", K, num_bits),
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self.running_sum,
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1,
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|| shifted.ok_or(Error::SynthesisError),
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)?;
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// Enable lookup for shifted element, to constrain it to 10 bits.
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self.q_lookup_short.enable(region, 1)?;
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Ok(())
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}
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}
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#[cfg(test)]
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mod tests {
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use super::super::{CellValue, UtilitiesInstructions, Var};
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use super::super::Var;
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use super::LookupRangeCheckConfig;
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use crate::primitives::sinsemilla::{INV_TWO_POW_K, K};
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use crate::spec::lebs2ip;
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use ff::PrimeFieldBits;
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use ff::{Field, PrimeFieldBits};
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use halo2::{
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circuit::{layouter::SingleChipLayouter, Layouter},
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dev::MockProver,
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dev::{MockProver, VerifyFailure},
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plonk::{Assignment, Circuit, ConstraintSystem, Error},
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};
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use pasta_curves::{arithmetic::FieldExt, pallas};
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@ -191,27 +382,23 @@ mod tests {
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#[test]
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fn lookup_range_check() {
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struct MyCircuit<F: FieldExt + PrimeFieldBits> {
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num_words: usize,
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_marker: PhantomData<F>,
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}
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impl<F: FieldExt + PrimeFieldBits> UtilitiesInstructions<F> for MyCircuit<F> {
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type Var = CellValue<F>;
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}
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impl<F: FieldExt + PrimeFieldBits> Circuit<F> for MyCircuit<F> {
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type Config = LookupRangeCheckConfig<F, K>;
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fn configure(meta: &mut ConstraintSystem<F>) -> Self::Config {
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let running_sum = meta.advice_column();
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let constants = meta.fixed_column();
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let table_idx = meta.fixed_column();
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let q_lookup = meta.fixed_column();
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let perm = meta.permutation(&[running_sum.into()]);
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let perm = meta.permutation(&[running_sum.into(), constants.into()]);
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LookupRangeCheckConfig::<F, K>::configure(
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meta,
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q_lookup,
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running_sum,
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constants,
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table_idx,
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perm,
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)
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|
@ -227,45 +414,51 @@ mod tests {
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// Load table_idx
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config.load(&mut layouter)?;
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let num_words = 6;
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// Lookup constraining element to be no longer than num_words * K bits.
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let elements_and_expected_final_zs = [
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(F::from_u64((1 << (num_words * K)) - 1), F::zero()), // a word that is within num_words * K bits long
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(F::from_u64(1 << (num_words * K)), F::one()), // a word that is just over num_words * K bits long
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(
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F::from_u64((1 << (self.num_words * K)) - 1),
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F::zero(),
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true,
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), // a word that is within self.num_words * K bits long
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(F::from_u64(1 << (self.num_words * K)), F::one(), false), // a word that is just over self.num_words * K bits long
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];
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for (element, expected_final_z) in elements_and_expected_final_zs.iter() {
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let expected_zs = expected_zs::<F, K>(*element, num_words);
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fn expected_zs<F: FieldExt + PrimeFieldBits, const K: usize>(
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element: F,
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num_words: usize,
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) -> Vec<F> {
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let chunks = {
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element
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.to_le_bits()
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.iter()
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.by_val()
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.take(num_words * K)
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.collect::<Vec<_>>()
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.chunks_exact(K)
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.map(|chunk| F::from_u64(lebs2ip::<K>(chunk.try_into().unwrap())))
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.collect::<Vec<_>>()
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};
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let expected_zs = {
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let inv_two_pow_k = F::from_bytes(&INV_TWO_POW_K).unwrap();
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chunks.iter().fold(vec![element], |mut zs, a_i| {
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// z_{i + 1} = (z_i - a_i) / 2^{K}
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let z = (zs[zs.len() - 1] - a_i) * inv_two_pow_k;
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zs.push(z);
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zs
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})
|
||||
};
|
||||
expected_zs
|
||||
}
|
||||
|
||||
// Load the value to be decomposed into the circuit.
|
||||
let element = self.load_private(
|
||||
layouter.namespace(|| "element"),
|
||||
config.running_sum,
|
||||
for (element, expected_final_z, strict) in elements_and_expected_final_zs.iter() {
|
||||
let expected_zs = expected_zs::<F, K>(*element, self.num_words);
|
||||
|
||||
let (_, zs) = config.witness_check(
|
||||
layouter.namespace(|| format!("Lookup {:?}", self.num_words)),
|
||||
Some(*element),
|
||||
)?;
|
||||
|
||||
// Although this fixed column assignment can be done
|
||||
// within the `lookup_range_check` method, in practice
|
||||
// the information needed to toggle the lookup depends
|
||||
// on some external business logic (e.g. whether the
|
||||
// top bit of `element` is set).
|
||||
//
|
||||
// Leaving the toggle assignment to the caller gives
|
||||
// them the freedom to define this business logic.
|
||||
let zs = layouter.assign_region(
|
||||
|| "word within range",
|
||||
|mut region| {
|
||||
for idx in 0..num_words {
|
||||
// Assign fixed column to activate lookup.
|
||||
region.assign_fixed(
|
||||
|| format!("lookup on row {}", idx),
|
||||
config.q_lookup,
|
||||
idx,
|
||||
|| Ok(F::one()),
|
||||
)?;
|
||||
}
|
||||
|
||||
config.lookup_range_check(&mut region, 0, element, num_words)
|
||||
},
|
||||
self.num_words,
|
||||
*strict,
|
||||
)?;
|
||||
|
||||
assert_eq!(*expected_zs.last().unwrap(), *expected_final_z);
|
||||
|
@ -276,13 +469,13 @@ mod tests {
|
|||
}
|
||||
}
|
||||
}
|
||||
|
||||
Ok(())
|
||||
}
|
||||
}
|
||||
|
||||
{
|
||||
let circuit: MyCircuit<pallas::Base> = MyCircuit {
|
||||
num_words: 6,
|
||||
_marker: PhantomData,
|
||||
};
|
||||
let prover = MockProver::<pallas::Base>::run(11, &circuit, vec![]).unwrap();
|
||||
|
@ -290,31 +483,150 @@ mod tests {
|
|||
}
|
||||
}
|
||||
|
||||
#[cfg(test)]
|
||||
fn expected_zs<F: FieldExt + PrimeFieldBits, const K: usize>(
|
||||
element: F,
|
||||
num_words: usize,
|
||||
) -> Vec<F> {
|
||||
let chunks = {
|
||||
element
|
||||
.to_le_bits()
|
||||
.iter()
|
||||
.by_val()
|
||||
.take(num_words * K)
|
||||
.collect::<Vec<_>>()
|
||||
.chunks_exact(K)
|
||||
.map(|chunk| F::from_u64(lebs2ip::<K>(chunk.try_into().unwrap())))
|
||||
.collect::<Vec<_>>()
|
||||
};
|
||||
let expected_zs = {
|
||||
let inv_two_pow_k = F::from_bytes(&INV_TWO_POW_K).unwrap();
|
||||
chunks.iter().fold(vec![element], |mut zs, a_i| {
|
||||
// z_{i + 1} = (z_i - a_i) / 2^{K}
|
||||
let z = (zs[zs.len() - 1] - a_i) * inv_two_pow_k;
|
||||
zs.push(z);
|
||||
zs
|
||||
})
|
||||
};
|
||||
expected_zs
|
||||
#[test]
|
||||
fn short_range_check() {
|
||||
struct MyCircuit<F: FieldExt + PrimeFieldBits> {
|
||||
element: Option<F>,
|
||||
num_bits: usize,
|
||||
_marker: PhantomData<F>,
|
||||
}
|
||||
|
||||
impl<F: FieldExt + PrimeFieldBits> Circuit<F> for MyCircuit<F> {
|
||||
type Config = LookupRangeCheckConfig<F, K>;
|
||||
|
||||
fn configure(meta: &mut ConstraintSystem<F>) -> Self::Config {
|
||||
let running_sum = meta.advice_column();
|
||||
let constants = meta.fixed_column();
|
||||
let table_idx = meta.fixed_column();
|
||||
let perm = meta.permutation(&[running_sum.into()]);
|
||||
|
||||
LookupRangeCheckConfig::<F, K>::configure(
|
||||
meta,
|
||||
running_sum,
|
||||
constants,
|
||||
table_idx,
|
||||
perm,
|
||||
)
|
||||
}
|
||||
|
||||
fn synthesize(
|
||||
&self,
|
||||
cs: &mut impl Assignment<F>,
|
||||
config: Self::Config,
|
||||
) -> Result<(), Error> {
|
||||
let mut layouter = SingleChipLayouter::new(cs)?;
|
||||
|
||||
// Load table_idx
|
||||
config.load(&mut layouter)?;
|
||||
|
||||
// Lookup constraining element to be no longer than num_bits.
|
||||
config.witness_short_check(
|
||||
layouter.namespace(|| format!("Lookup {:?} bits", self.num_bits)),
|
||||
self.element,
|
||||
self.num_bits,
|
||||
)?;
|
||||
|
||||
Ok(())
|
||||
}
|
||||
}
|
||||
|
||||
// Edge case: zero bits
|
||||
{
|
||||
let circuit: MyCircuit<pallas::Base> = MyCircuit {
|
||||
element: Some(pallas::Base::zero()),
|
||||
num_bits: 0,
|
||||
_marker: PhantomData,
|
||||
};
|
||||
let prover = MockProver::<pallas::Base>::run(11, &circuit, vec![]).unwrap();
|
||||
assert_eq!(prover.verify(), Ok(()));
|
||||
}
|
||||
|
||||
// Edge case: K bits
|
||||
{
|
||||
let circuit: MyCircuit<pallas::Base> = MyCircuit {
|
||||
element: Some(pallas::Base::from_u64((1 << K) - 1)),
|
||||
num_bits: K,
|
||||
_marker: PhantomData,
|
||||
};
|
||||
let prover = MockProver::<pallas::Base>::run(11, &circuit, vec![]).unwrap();
|
||||
assert_eq!(prover.verify(), Ok(()));
|
||||
}
|
||||
|
||||
// Element within `num_bits`
|
||||
{
|
||||
let circuit: MyCircuit<pallas::Base> = MyCircuit {
|
||||
element: Some(pallas::Base::from_u64((1 << 6) - 1)),
|
||||
num_bits: 6,
|
||||
_marker: PhantomData,
|
||||
};
|
||||
let prover = MockProver::<pallas::Base>::run(11, &circuit, vec![]).unwrap();
|
||||
assert_eq!(prover.verify(), Ok(()));
|
||||
}
|
||||
|
||||
// Element larger than `num_bits` but within K bits
|
||||
{
|
||||
let circuit: MyCircuit<pallas::Base> = MyCircuit {
|
||||
element: Some(pallas::Base::from_u64(1 << 6)),
|
||||
num_bits: 6,
|
||||
_marker: PhantomData,
|
||||
};
|
||||
let prover = MockProver::<pallas::Base>::run(11, &circuit, vec![]).unwrap();
|
||||
assert_eq!(
|
||||
prover.verify(),
|
||||
Err(vec![VerifyFailure::Lookup {
|
||||
lookup_index: 1,
|
||||
row: 1
|
||||
}])
|
||||
);
|
||||
}
|
||||
|
||||
// Element larger than K bits
|
||||
{
|
||||
let circuit: MyCircuit<pallas::Base> = MyCircuit {
|
||||
element: Some(pallas::Base::from_u64(1 << K)),
|
||||
num_bits: 6,
|
||||
_marker: PhantomData,
|
||||
};
|
||||
let prover = MockProver::<pallas::Base>::run(11, &circuit, vec![]).unwrap();
|
||||
assert_eq!(
|
||||
prover.verify(),
|
||||
Err(vec![
|
||||
VerifyFailure::Lookup {
|
||||
lookup_index: 1,
|
||||
row: 0
|
||||
},
|
||||
VerifyFailure::Lookup {
|
||||
lookup_index: 1,
|
||||
row: 1
|
||||
},
|
||||
])
|
||||
);
|
||||
}
|
||||
|
||||
// Element which is not within `num_bits`, but which has a shifted value within
|
||||
// num_bits
|
||||
{
|
||||
let num_bits = 6;
|
||||
let shifted = pallas::Base::from_u64((1 << num_bits) - 1);
|
||||
// Recall that shifted = element * 2^{K-s}
|
||||
// => element = shifted * 2^{s-K}
|
||||
let element = shifted
|
||||
* pallas::Base::from_u64(1 << (K as u64 - num_bits))
|
||||
.invert()
|
||||
.unwrap();
|
||||
let circuit: MyCircuit<pallas::Base> = MyCircuit {
|
||||
element: Some(element),
|
||||
num_bits: num_bits as usize,
|
||||
_marker: PhantomData,
|
||||
};
|
||||
let prover = MockProver::<pallas::Base>::run(11, &circuit, vec![]).unwrap();
|
||||
assert_eq!(
|
||||
prover.verify(),
|
||||
Err(vec![VerifyFailure::Lookup {
|
||||
lookup_index: 1,
|
||||
row: 0
|
||||
}])
|
||||
);
|
||||
}
|
||||
}
|
||||
}
|
||||
|
|
Loading…
Reference in New Issue