From 55d0f2e340f73eb2bd8cc35f513133d5774f3a51 Mon Sep 17 00:00:00 2001
From: ljedrz <ljedrz@gmail.com>
Date: Thu, 22 Oct 2020 12:09:30 +0200
Subject: [PATCH] perf: reduce allocations in the Neg impl for Vec<Boolean>

Signed-off-by: ljedrz <ljedrz@gmail.com>
---
 gadgets/src/arithmetic/neg.rs | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/gadgets/src/arithmetic/neg.rs b/gadgets/src/arithmetic/neg.rs
index ba199c8eda..a35f474f46 100644
--- a/gadgets/src/arithmetic/neg.rs
+++ b/gadgets/src/arithmetic/neg.rs
@@ -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