forked from zcash/halo2
-
Notifications
You must be signed in to change notification settings - Fork 129
/
lookup.rs
72 lines (66 loc) · 2.81 KB
/
lookup.rs
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
use super::circuit::Expression;
use ff::Field;
pub(crate) mod prover;
pub(crate) mod verifier;
#[derive(Clone, Debug)]
pub(crate) struct Argument<F: Field> {
pub input_expressions: Vec<Expression<F>>,
pub table_expressions: Vec<Expression<F>>,
}
impl<F: Field> Argument<F> {
/// Constructs a new lookup argument.
///
/// `table_map` is a sequence of `(input, table)` tuples.
pub fn new(table_map: Vec<(Expression<F>, Expression<F>)>) -> Self {
let (input_expressions, table_expressions) = table_map.into_iter().unzip();
Argument {
input_expressions,
table_expressions,
}
}
pub(crate) fn required_degree(&self) -> usize {
assert_eq!(self.input_expressions.len(), self.table_expressions.len());
// The first value in the permutation poly should be one.
// degree 2:
// l_0(X) * (1 - z(X)) = 0
//
// The "last" value in the permutation poly should be a boolean, for
// completeness and soundness.
// degree 3:
// l_last(X) * (z(X)^2 - z(X)) = 0
//
// Enable the permutation argument for only the rows involved.
// degree (2 + input_degree + table_degree) or 4, whichever is larger:
// (1 - (l_last(X) + l_blind(X))) * (
// z(\omega X) (a'(X) + \beta) (s'(X) + \gamma)
// - z(X) (\theta^{m-1} a_0(X) + ... + a_{m-1}(X) + \beta) (\theta^{m-1} s_0(X) + ... + s_{m-1}(X) + \gamma)
// ) = 0
//
// The first two values of a' and s' should be the same.
// degree 2:
// l_0(X) * (a'(X) - s'(X)) = 0
//
// Either the two values are the same, or the previous
// value of a' is the same as the current value.
// degree 3:
// (1 - (l_last(X) + l_blind(X))) * (a′(X) − s′(X))⋅(a′(X) − a′(\omega^{-1} X)) = 0
let mut input_degree = 1;
for expr in self.input_expressions.iter() {
input_degree = std::cmp::max(input_degree, expr.degree());
}
let mut table_degree = 1;
for expr in self.table_expressions.iter() {
table_degree = std::cmp::max(table_degree, expr.degree());
}
// In practice because input_degree and table_degree are initialized to
// one, the latter half of this max() invocation is at least 4 always,
// rendering this call pointless except to be explicit in case we change
// the initialization of input_degree/table_degree in the future.
std::cmp::max(
// (1 - (l_last + l_blind)) z(\omega X) (a'(X) + \beta) (s'(X) + \gamma)
4,
// (1 - (l_last + l_blind)) z(X) (\theta^{m-1} a_0(X) + ... + a_{m-1}(X) + \beta) (\theta^{m-1} s_0(X) + ... + s_{m-1}(X) + \gamma)
2 + input_degree + table_degree,
)
}
}