zec
/
halo2
mirror of https://github.com/zcash/halo2.git
1
0
Fork 0
Code Issues Projects Releases Wiki Activity

gadget::utilities: Introduce ternary expression helper.

This commit is contained in:
therealyingtong 2021-11-30 10:39:01 -05:00
parent e0a0a0d509
commit ba75da27bb
1 changed files with 8 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
src/circuit/gadget/utilities.rs
View File

@ -105,6 +105,14 @@ pub fn bool_check<F: FieldExt>(value: Expression<F>) -> Expression<F> {
range_check(value, 2) range_check(value, 2)
} }
/// If `a` then `b`, else `c`. Returns (a * b) + (1 - a) * c.
///
/// `a` must be a boolean-constrained expression.
pub fn ternary<F: FieldExt>(a: Expression<F>, b: Expression<F>, c: Expression<F>) -> Expression<F> {
let one_minus_a = Expression::Constant(F::one()) - a.clone();
a * b + one_minus_a * c
}
/// Takes a specified subsequence of the little-endian bit representation of a field element. /// Takes a specified subsequence of the little-endian bit representation of a field element.
/// The bits are numbered from 0 for the LSB. /// The bits are numbered from 0 for the LSB.
pub fn bitrange_subset<F: FieldExt + PrimeFieldBits>(field_elem: F, bitrange: Range<usize>) -> F { pub fn bitrange_subset<F: FieldExt + PrimeFieldBits>(field_elem: F, bitrange: Range<usize>) -> F {