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perf: reduce allocations in the Neg impl for Vec<Boolean>

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Signed-off-by: ljedrz <ljedrz@gmail.com>
This commit is contained in:
ljedrz 2020-10-22 12:09:30 +02:00
parent 1e25738890
commit 55d0f2e340
1 changed files with 5 additions and 2 deletions
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7
gadgets/src/arithmetic/neg.rs
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@ -22,6 +22,8 @@ use snarkos_models::{
gadgets::{r1cs::ConstraintSystem, utilities::boolean::Boolean},
};
use std::iter;
/// Returns a negated representation of `self` in the constraint system.
pub trait Neg<F: Field>
where
@ -40,8 +42,9 @@ impl<F: Field> Neg<F> for Vec<Boolean> {
let flipped: Self = self.iter().map(|bit| bit.not()).collect();
// add one
let mut one = vec![Boolean::constant(true)];
one.append(&mut vec![Boolean::Constant(false); self.len() - 1]);
let mut one = Vec::with_capacity(self.len());
one.push(Boolean::constant(true));
one.extend(iter::repeat(Boolean::Constant(false)).take(self.len() - 1));
let mut bits = flipped.add_bits(cs.ns(|| "add one"), &one)?;
let _carry = bits.pop(); // we already accounted for overflow above