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RandomAccessGate documentation

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This commit is contained in:
Nicholas Ward 2022-08-24 18:03:13 -07:00
parent df15031145
commit 0ac0975d95
1 changed files with 18 additions and 2 deletions
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20
plonky2/src/gates/random_access.rs
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@ -24,9 +24,15 @@ use crate::plonk::vars::{
/// A gate for checking that a particular element of a list matches a given value.
#[derive(Copy, Clone, Debug)]
pub struct RandomAccessGate<F: RichField + Extendable<D>, const D: usize> {
// Number of bits in the index (log2 of the list size).
pub bits: usize,
// How many separate copies are packed into one gate.
pub num_copies: usize,
// Leftover wires are used as global scratch space to store constants.
pub num_extra_constants: usize,
_phantom: PhantomData<F>,
}
@ -41,13 +47,18 @@ impl<F: RichField + Extendable<D>, const D: usize> RandomAccessGate<F, D> {
}
pub fn new_from_config(config: &CircuitConfig, bits: usize) -> Self {
// We can access a list of 2^bits elements.
let vec_size = 1 << bits;
// Need `(2 + vec_size) * num_copies` routed wires
// We need `(2 + vec_size) * num_copies` routed wires.
let max_copies = (config.num_routed_wires / (2 + vec_size)).min(
// Need `(2 + vec_size + bits) * num_copies` wires
// We need `(2 + vec_size + bits) * num_copies` wires in total.
config.num_wires / (2 + vec_size + bits),
);
// Any leftover wires can be used for constants.
let max_extra_constants = config.num_routed_wires - (2 + vec_size) * max_copies;
Self::new(
max_copies,
bits,
@ -55,20 +66,24 @@ impl<F: RichField + Extendable<D>, const D: usize> RandomAccessGate<F, D> {
)
}
// Length of the list being accessed.
fn vec_size(&self) -> usize {
1 << self.bits
}
// For each copy, a wire containing the claimed index of the element.
pub fn wire_access_index(&self, copy: usize) -> usize {
debug_assert!(copy < self.num_copies);
(2 + self.vec_size()) * copy
}
// For each copy, a wire containing the element claimed to be at the index.
pub fn wire_claimed_element(&self, copy: usize) -> usize {
debug_assert!(copy < self.num_copies);
(2 + self.vec_size()) * copy + 1
}
// For each copy, wires containing the entire list.
pub fn wire_list_item(&self, i: usize, copy: usize) -> usize {
debug_assert!(i < self.vec_size());
debug_assert!(copy < self.num_copies);
@ -84,6 +99,7 @@ impl<F: RichField + Extendable<D>, const D: usize> RandomAccessGate<F, D> {
self.start_extra_constants() + i
}
// All above wires are routed.
pub fn num_routed_wires(&self) -> usize {
self.start_extra_constants() + self.num_extra_constants
}