From 5dd4ed3e1c5c63137a7994942c09cc31132d310f Mon Sep 17 00:00:00 2001
From: Nicholas Ward <npward@berkeley.edu>
Date: Mon, 1 Nov 2021 11:12:21 -0700
Subject: [PATCH] addressed comments

---
 src/gadgets/arithmetic_u32.rs | 15 +--------------
 src/gadgets/biguint.rs        |  4 ++--
 src/gates/subtraction_u32.rs  |  2 +-
 3 files changed, 4 insertions(+), 17 deletions(-)

diff --git a/src/gadgets/arithmetic_u32.rs b/src/gadgets/arithmetic_u32.rs
index db6d3669..ba076a8f 100644
--- a/src/gadgets/arithmetic_u32.rs
+++ b/src/gadgets/arithmetic_u32.rs
@@ -81,24 +81,11 @@ impl<F: RichField + Extendable<D>, const D: usize> CircuitBuilder<F, D> {
         self.mul_add_u32(a, one, b)
     }
 
-    pub fn add_three_u32(
-        &mut self,
-        a: U32Target,
-        b: U32Target,
-        c: U32Target,
-    ) -> (U32Target, U32Target) {
-        let (init_low, carry1) = self.add_u32(a, b);
-        let (final_low, carry2) = self.add_u32(c, init_low);
-        let (combined_carry, _zero) = self.add_u32(carry1, carry2);
-        (final_low, combined_carry)
-    }
-
-    pub fn add_many_u32(&mut self, to_add: Vec<U32Target>) -> (U32Target, U32Target) {
+    pub fn add_many_u32(&mut self, to_add: &[U32Target]) -> (U32Target, U32Target) {
         match to_add.len() {
             0 => (self.zero_u32(), self.zero_u32()),
             1 => (to_add[0], self.zero_u32()),
             2 => self.add_u32(to_add[0], to_add[1]),
-            3 => self.add_three_u32(to_add[0], to_add[1], to_add[2]),
             _ => {
                 let (mut low, mut carry) = self.add_u32(to_add[0], to_add[1]);
                 for i in 2..to_add.len() {
diff --git a/src/gadgets/biguint.rs b/src/gadgets/biguint.rs
index 81880eef..a524a79b 100644
--- a/src/gadgets/biguint.rs
+++ b/src/gadgets/biguint.rs
@@ -117,7 +117,7 @@ impl<F: RichField + Extendable<D>, const D: usize> CircuitBuilder<F, D> {
                 self.zero_u32()
             };
 
-            let (new_limb, new_carry) = self.add_three_u32(carry.clone(), a_limb, b_limb);
+            let (new_limb, new_carry) = self.add_many_u32(&[carry.clone(), a_limb, b_limb]);
             carry = new_carry;
             combined_limbs.push(new_limb);
         }
@@ -164,7 +164,7 @@ impl<F: RichField + Extendable<D>, const D: usize> CircuitBuilder<F, D> {
         let mut carry = self.zero_u32();
         for i in 0..total_limbs {
             to_add[i].push(carry);
-            let (new_result, new_carry) = self.add_many_u32(to_add[i].clone());
+            let (new_result, new_carry) = self.add_many_u32(&to_add[i].clone());
             combined_limbs.push(new_result);
             carry = new_carry;
         }
diff --git a/src/gates/subtraction_u32.rs b/src/gates/subtraction_u32.rs
index c11c6f0f..afac85be 100644
--- a/src/gates/subtraction_u32.rs
+++ b/src/gates/subtraction_u32.rs
@@ -15,7 +15,7 @@ use crate::plonk::vars::{EvaluationTargets, EvaluationVars, EvaluationVarsBase};
 pub const NUM_U32_SUBTRACTION_OPS: usize = 3;
 
 /// A gate to perform a subtraction on 32-bit limbs: given `x`, `y`, and `borrow`, it returns
-/// the result `x - y - borrow` and, if this underflows, a new `borrow`.
+/// the result `x - y - borrow` and, if this underflows, a new `borrow`. Inputs are not range-checked.
 #[derive(Clone, Debug)]
 pub struct U32SubtractionGate<F: RichField + Extendable<D>, const D: usize> {
     _phantom: PhantomData<F>,