feat: replace bitwise ORs in U256:from_bytes32 with addition (Aztec…

…Protocol#3947)

Addition and OR are the same here due to the lack of overlaps in the bit
representations of the bytes making up each u64. It's then more
efficient to just add them together.

yarn-project/noir-protocol-circuits/src/crates/types/src/utils/uint256.nr

@@ -14,41 +14,42 @@ struct U256 {
 
 impl U256 {
     pub fn from_bytes32(bytes : [u8;32]) -> U256 {
+        // We use addition rather than a bitwise OR as the bitshifts ensure that none of the bytes overlap each other.
         let high_0 = ((bytes[0] as u64) << 56)
-                | ((bytes[1] as u64) << 48)
-                | ((bytes[2] as u64) << 40)
-                | ((bytes[3] as u64) << 32)
-                | ((bytes[4] as u64) << 24)
-                | ((bytes[5] as u64) << 16)
-                | ((bytes[6] as u64) << 8)
-                |  (bytes[7] as u64);
+                + ((bytes[1] as u64) << 48)
+                + ((bytes[2] as u64) << 40)
+                + ((bytes[3] as u64) << 32)
+                + ((bytes[4] as u64) << 24)
+                + ((bytes[5] as u64) << 16)
+                + ((bytes[6] as u64) << 8)
+                +  (bytes[7] as u64);
 
         let high_1 = ((bytes[8] as u64) << 56)
-                | ((bytes[9] as u64) << 48)
-                | ((bytes[10] as u64) << 40)
-                | ((bytes[11] as u64) << 32)
-                | ((bytes[12] as u64) << 24)
-                | ((bytes[13] as u64) << 16)
-                | ((bytes[14] as u64) << 8)
-                |  (bytes[15] as u64);
+                + ((bytes[9] as u64) << 48)
+                + ((bytes[10] as u64) << 40)
+                + ((bytes[11] as u64) << 32)
+                + ((bytes[12] as u64) << 24)
+                + ((bytes[13] as u64) << 16)
+                + ((bytes[14] as u64) << 8)
+                +  (bytes[15] as u64);
 
         let low_0 = ((bytes[16] as u64) << 56)
-                | ((bytes[17] as u64) << 48)
-                | ((bytes[18] as u64) << 40)
-                | ((bytes[19] as u64) << 32)
-                | ((bytes[20] as u64) << 24)
-                | ((bytes[21] as u64) << 16)
-                | ((bytes[22] as u64) << 8)
-                |  (bytes[23] as u64);
+                + ((bytes[17] as u64) << 48)
+                + ((bytes[18] as u64) << 40)
+                + ((bytes[19] as u64) << 32)
+                + ((bytes[20] as u64) << 24)
+                + ((bytes[21] as u64) << 16)
+                + ((bytes[22] as u64) << 8)
+                +  (bytes[23] as u64);
 
         let low_1 = ((bytes[24] as u64) << 56)
-                | ((bytes[25] as u64) << 48)
-                | ((bytes[26] as u64) << 40)
-                | ((bytes[27] as u64) << 32)
-                | ((bytes[28] as u64) << 24)
-                | ((bytes[29] as u64) << 16)
-                | ((bytes[30] as u64) << 8)
-                |  (bytes[31] as u64);
+                + ((bytes[25] as u64) << 48)
+                + ((bytes[26] as u64) << 40)
+                + ((bytes[27] as u64) << 32)
+                + ((bytes[28] as u64) << 24)
+                + ((bytes[29] as u64) << 16)
+                + ((bytes[30] as u64) << 8)
+                +  (bytes[31] as u64);
 
         U256{inner : [high_0, high_1, low_0, low_1]}
     }