Add comments & improve expression performance

hashes/zkevm/src/keccak/keccak_packed_multi.rs

@@ -141,8 +141,7 @@ pub struct KeccakTable {
     pub input_rlc: Column<Advice>, // RLC of input bytes
     // Byte array input length
     pub input_len: Column<Advice>,
-    // /// RLC of the hash result
-    // pub output_rlc: Column<Advice>, // RLC of hash of input bytes
+    /// Output of the hash function
     pub output: Word<Column<Advice>>,
 }
 

hashes/zkevm/src/keccak/mod.rs

@@ -1180,7 +1180,7 @@ pub fn keccak_phase0<F: Field>(
                 ));
             }
 
-            // The rlc of the hash
+            // Assign the hash result
             let is_final = is_final_block && round == NUM_ROUNDS;
             hash = if is_final {
                 let hash_bytes_le = s

hashes/zkevm/src/util/expression.rs

@@ -135,9 +135,13 @@ pub mod from_bytes {
     pub fn value<F: PrimeField>(bytes: &[u8]) -> F {
         let mut value = F::ZERO;
         let mut multiplier = F::ONE;
-        for byte in bytes.iter() {
-            value += F::from(*byte as u64) * multiplier;
-            multiplier *= F::from(256);
+        let two_pow_64 = F::from_u128(1 << 64);
+        let two_pow_128 = two_pow_64 * two_pow_64;
+        for u128_chunk in bytes.chunks(u128::BITS as usize / u8::BITS as usize) {
+            let mut buffer = [0; 16];
+            buffer[..u128_chunk.len()].copy_from_slice(u128_chunk);
+            value += F::from_u128(u128::from_le_bytes(buffer)) * multiplier;
+            multiplier *= two_pow_128;
         }
         value
     }