feat(blockifier): Add get_syscall_gas_cost to versioned constants impl

crates/blockifier/src/versioned_constants.rs

@@ -20,6 +20,7 @@ use starknet_api::execution_resources::GasAmount;
 use starknet_api::transaction::fields::GasVectorComputationMode;
 use strum::IntoEnumIterator;
 use thiserror::Error;
+use crate::utils::u64_from_usize;
 
 use crate::execution::deprecated_syscalls::hint_processor::SyscallCounter;
 use crate::execution::execution_utils::poseidon_hash_many_cost;
@@ -330,6 +331,28 @@ impl VersionedConstants {
             GasVectorComputationMode::NoL2Gas => &self.deprecated_l2_resource_gas_costs,
         }
     }
+
+    /// Calculates a syscall's gas costs from the os resources
+    pub fn get_syscall_gas_cost(&self, syscall_selector: &SyscallSelector) -> u64 {
+        let gas_costs = &self.os_constants.gas_costs;
+        let execution_resources = &self
+            .os_resources
+            .execute_syscalls
+            .get(syscall_selector)
+            .expect("Fetching the execution resources of a syscall should not fail.");
+        let n_steps = u64_from_usize(execution_resources.n_steps);
+        let n_memory_holes = u64_from_usize(execution_resources.n_memory_holes);
+        let mut total_builtin_gas_cost: u64 = 0;
+        for (builtin, amount) in &execution_resources.builtin_instance_counter {
+            let builtin_cost = gas_costs.get_builtin_gas_cost(builtin).unwrap_or_else(|err| panic!("Failed to get gas cost: {}", err));
+            total_builtin_gas_cost += builtin_cost * u64_from_usize(*amount);
+        }
+
+
+        std::cmp::max(n_steps * gas_costs.step_gas_cost
+            + n_memory_holes * gas_costs.memory_hole_gas_cost
+            + total_builtin_gas_cost, gas_costs.syscall_base_gas_cost)
+    }
 }
 
 #[derive(Clone, Debug, Default, Deserialize, Eq, PartialEq)]

crates/blockifier/src/versioned_constants_test.rs

@@ -167,3 +167,17 @@ fn test_all_jsons_in_enum() {
 fn test_latest_no_panic() {
     VersionedConstants::latest_constants();
 }
+
+#[test]
+fn test_correct_syscall_gas_cost_calculation() {
+    const EXPECTED_CALL_CONTRACT_GAS_COST : u64 = 87650;
+    const EXPECTED_SECP256K1MUL_GAS_COST : u64 = 8143650;
+    const EXPECTED_SHA256PROCESSBLOCK_GAS_COST : u64 = 841095;
+
+
+    let versioned_constants = VersionedConstants::latest_constants().clone();
+
+    assert_eq!(versioned_constants.get_syscall_gas_cost(&SyscallSelector::CallContract), EXPECTED_CALL_CONTRACT_GAS_COST);
+    assert_eq!(versioned_constants.get_syscall_gas_cost(&SyscallSelector::Secp256k1Mul), EXPECTED_SECP256K1MUL_GAS_COST);
+    assert_eq!(versioned_constants.get_syscall_gas_cost(&SyscallSelector::Sha256ProcessBlock), EXPECTED_SHA256PROCESSBLOCK_GAS_COST);
+}