implement fixed point division

crates/optimism/src/handler_register.rs

@@ -711,20 +711,20 @@ mod tests {
         db.insert_account_info(
             caller,
             AccountInfo {
-                balance: U256::from(10_501),
+                balance: U256::from(151),
                 ..Default::default()
             },
         );
         let mut context = Context::<TestMemOpWiring>::new_with_db(db);
         *context.evm.chain.l1_block_info_mut() = Some(L1BlockInfo {
-            operator_fee_scalar: Some(U256::from(1_000)),
-            operator_fee_constant: Some(U256::from(500)),
+            operator_fee_scalar: Some(U256::from(10_000_000)),
+            operator_fee_constant: Some(U256::from(50)),
             ..Default::default()
         });
         context.evm.inner.env.tx.base.gas_limit = 10;
 
-        // operator fee cost is operator_fee_scalar * gas_limit + operator_fee_constant
-        // 1_000 * 10 + 500 = 10_500
+        // operator fee cost is operator_fee_scalar * gas_limit / 1e6 + operator_fee_constant
+        // 10_000_000 * 10 / 1_000_000 + 50 = 150
         context.evm.inner.env.tx.enveloped_tx = Some(bytes!("FACADE"));
         deduct_caller::<TestMemOpWiring, HoloceneSpec>(&mut context).unwrap();
 

crates/optimism/src/l1block.rs

@@ -24,6 +24,11 @@ const OPERATOR_FEE_SCALAR_OFFSET: usize = 4;
 /// the storage slot of the 8-byte operatorFeeConstant attribute.
 const OPERATOR_FEE_CONSTANT_OFFSET: usize = 8;
 
+/// The fixed point decimal scaling factor associated with the operator fee scalar.
+///
+/// Allows users to use 6 decimal points of precision when specifying the operator_fee_scalar.
+const OPERATOR_FEE_SCALAR_DECIMAL: u64 = 1_000_000;
+
 const L1_BASE_FEE_SLOT: U256 = U256::from_limbs([1u64, 0, 0, 0]);
 const L1_OVERHEAD_SLOT: U256 = U256::from_limbs([5u64, 0, 0, 0]);
 const L1_SCALAR_SLOT: U256 = U256::from_limbs([6u64, 0, 0, 0]);
@@ -211,9 +216,10 @@ impl L1BlockInfo {
             .operator_fee_constant
             .expect("Missing operator fee constant for holocene L1 Block");
 
-        gas_limit
-            .saturating_mul(operator_fee_scalar)
-            .saturating_add(operator_fee_constant)
+        let product = gas_limit.saturating_mul(operator_fee_scalar)
+            / (U256::from(OPERATOR_FEE_SCALAR_DECIMAL));
+
+        product.saturating_add(operator_fee_constant)
     }
 
     /// Calculate the operator fee for executing this transaction.