From 9f3da35a8ac3107190f8c85c8cf3ea1a0f8780a4 Mon Sep 17 00:00:00 2001
From: miguelis <miguelis@ucm.es>
Date: Wed, 3 Jul 2024 19:50:10 +0200
Subject: [PATCH]  Update ~-operator to use 254 bits instead of 256

---
 circom_algebra/src/algebra.rs            |  4 ++--
 circom_algebra/src/modular_arithmetic.rs | 12 ++++++------
 constraint_generation/src/execute.rs     |  2 +-
 3 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/circom_algebra/src/algebra.rs b/circom_algebra/src/algebra.rs
index bfddd49e2..bb3a47b46 100644
--- a/circom_algebra/src/algebra.rs
+++ b/circom_algebra/src/algebra.rs
@@ -554,13 +554,13 @@ impl<C: Default + Clone + Display + Hash + Eq> ArithmeticExpression<C> {
     }
 
     // Bit operations
-    pub fn complement_256(
+    pub fn complement_254(
         elem: &ArithmeticExpression<C>,
         field: &BigInt,
     ) -> ArithmeticExpression<C> {
         use ArithmeticExpression::*;
         if let Number { value } = elem {
-            Number { value: modular_arithmetic::complement_256(value, field) }
+            Number { value: modular_arithmetic::complement_254(value, field) }
         } else {
             NonQuadratic
         }
diff --git a/circom_algebra/src/modular_arithmetic.rs b/circom_algebra/src/modular_arithmetic.rs
index 6fdfce35a..4eb9cc728 100644
--- a/circom_algebra/src/modular_arithmetic.rs
+++ b/circom_algebra/src/modular_arithmetic.rs
@@ -92,13 +92,13 @@ pub fn multi_inv(values: &Vec<BigInt>, field: &BigInt) -> Vec<BigInt>{
 
 //Bit operations
 
-// 256 bit complement
-pub fn complement_256(elem: &BigInt, field: &BigInt) -> BigInt {
+// 254 bit complement
+pub fn complement_254(elem: &BigInt, field: &BigInt) -> BigInt {
     let (sign, mut bit_repr) = bit_representation(elem);
-    while bit_repr.len() > 256 {
+    while bit_repr.len() > 254 {
         bit_repr.pop();
     }
-    for _i in bit_repr.len()..256 {
+    for _i in bit_repr.len()..254 {
         bit_repr.push(0);
     }
     for bit in &mut bit_repr {
@@ -252,8 +252,8 @@ mod tests {
             .expect("generating the big int was not possible");
         let big_num = BigInt::parse_bytes("1234".as_bytes(), 10)
             .expect("generating the big int was not possible");
-        let big_num_complement = complement_256(&big_num, &field);
-        let big_num_complement_complement = complement_256(&big_num_complement, &field);
+        let big_num_complement = complement_254(&big_num, &field);
+        let big_num_complement_complement = complement_254(&big_num_complement, &field);
         let big_num_modulus = modulus(&big_num, &field);
         assert_eq!(big_num_complement_complement, big_num_modulus);
     }
diff --git a/constraint_generation/src/execute.rs b/constraint_generation/src/execute.rs
index 51704922c..887d52c38 100644
--- a/constraint_generation/src/execute.rs
+++ b/constraint_generation/src/execute.rs
@@ -2079,7 +2079,7 @@ fn execute_prefix_op(
     let result = match prefix_op {
         BoolNot => AExpr::not(value, field),
         Sub => AExpr::prefix_sub(value, field),
-        Complement => AExpr::complement_256(value, field),
+        Complement => AExpr::complement_254(value, field),
     };
     Result::Ok(result)
 }