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docs: fix coset index little-endian and correct panic conditions #188

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docs: fix coset index little-endian and correct panic conditions #188

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19 changes: 11 additions & 8 deletions src/poly/domain/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -58,7 +58,7 @@ impl<F: PrimeField> Radix2DomainVar<F> {
1 << self.dim
}

/// Returns offset, offset*g, offset*g^2, ..., offset*g^{coset_size}
/// Returns offset, offset*g, offset*g^2, ..., offset*g^{coset_size-1}
pub fn elements(&self) -> Vec<FpVar<F>> {
let mut result = Vec::new();
result.push(self.offset.clone());
Expand All @@ -75,13 +75,14 @@ impl<F: PrimeField> Radix2DomainVar<F> {
}

/// For domain `h<g>` with dimension `n`, `position` represented by
/// `query_pos` in big endian form, returns all points of
/// `query_pos` in little-endian (LSB-first) form, returns all points of
/// `h*g^{position}<g^{2^{n-coset_dim}}>`. The result is the query coset at
/// index `query_pos` for the FRI protocol.
///
/// # Panics
/// This function panics when `query_pos.len() != coset_dim` or
/// `query_pos.len() != self.dim`.
/// This function panics when `query_pos.len() < (self.dim - coset_dim)`.
/// Only the lowest `(self.dim - coset_dim)` bits of `query_pos` are used to
/// determine the coset index; any higher bits are ignored.
pub fn query_position_to_coset_elements(
&self,
query_pos: &[Boolean<F>],
Expand All @@ -93,11 +94,13 @@ impl<F: PrimeField> Radix2DomainVar<F> {
}

/// For domain `h<g>` with dimension `n`, `position` represented by
/// `query_pos` in big endian form, returns all points of
/// `h*g^{position}<g^{n-query_pos.len()}>`
/// `query_pos` in little-endian (LSB-first) form, returns all points of
/// `h*g^{position}<g^{n-query_pos.len()}>`.
///
/// # Panics
/// This function panics when `query_pos.len() < log2_num_cosets`.
/// This function panics when `query_pos.len() < (self.dim - coset_dim)`.
/// Only the lowest `(self.dim - coset_dim)` bits of `query_pos` are used to
/// determine the coset index; any higher bits are ignored.
pub fn query_position_to_coset(
&self,
query_pos: &[Boolean<F>],
Expand All @@ -106,7 +109,7 @@ impl<F: PrimeField> Radix2DomainVar<F> {
let coset_index = truncate_to_coset_index(query_pos, self.dim, coset_dim);
let offset_var = &self.offset * FpVar::Constant(self.gen).pow_le(&coset_index)?;
Ok(Self {
gen: self.gen.pow(&[1 << (self.dim - coset_dim)]), // distance between coset
gen: self.gen.pow(&[1 << (self.dim - coset_dim)]), // spacing between elements within the coset
offset: offset_var,
dim: coset_dim,
})
Expand Down