feat: returndatacopy (#500)

closes #484

cairo/ethereum/cancun/vm/instructions/environment.cairo

@@ -3,6 +3,7 @@ from starkware.cairo.common.registers import get_fp_and_pc
 from starkware.cairo.common.dict_access import DictAccess
 from starkware.cairo.common.math import split_felt
 from starkware.cairo.common.uint256 import uint256_lt
+from starkware.cairo.common.math_cmp import is_le
 
 from ethereum_types.bytes import Bytes32, Bytes32Struct
 from ethereum_types.numeric import U256, U256Struct, Uint, UnionUintU256, UnionUintU256Enum
@@ -14,7 +15,7 @@ from ethereum_types.others import (
 )
 from ethereum.cancun.fork_types import Address, SetAddress, SetAddressStruct, SetAddressDictAccess
 from ethereum.cancun.vm import Evm, EvmImpl, EnvImpl
-from ethereum.cancun.vm.exceptions import ExceptionalHalt, OutOfGasError
+from ethereum.cancun.vm.exceptions import ExceptionalHalt, OutOfGasError, OutOfBoundsRead
 from ethereum.cancun.vm.gas import charge_gas, GasConstants, calculate_gas_extend_memory
 from ethereum.cancun.vm.memory import buffer_read, memory_write, expand_by
 from ethereum.cancun.vm.stack import Stack, push, pop
@@ -278,6 +279,75 @@ func returndatasize{range_check_ptr, evm: Evm}() -> ExceptionalHalt* {
     return ok;
 }
 
+func returndatacopy{range_check_ptr: felt, evm: Evm}() -> ExceptionalHalt* {
+    alloc_locals;
+    // STACK
+    let stack = evm.value.stack;
+    with stack {
+        let (memory_start_index, err) = pop();
+        if (cast(err, felt) != 0) {
+            return err;
+        }
+        let (returndata_start_position, err) = pop();
+        if (cast(err, felt) != 0) {
+            return err;
+        }
+        let (size, err) = pop();
+        if (cast(err, felt) != 0) {
+            return err;
+        }
+    }
+    if (size.value.high != 0) {
+        tempvar err = new ExceptionalHalt(OutOfGasError);
+        return err;
+    }
+
+    let ceil32_size = ceil32(Uint(size.value.low));
+    let (words, _) = divmod(ceil32_size.value, 32);
+    let return_data_copy_gas_cost = GasConstants.GAS_RETURN_DATA_COPY * words;
+    // Calculate memory expansion cost
+    tempvar extensions_tuple = new TupleU256U256(new TupleU256U256Struct(memory_start_index, size));
+    tempvar extensions_list = ListTupleU256U256(new ListTupleU256U256Struct(extensions_tuple, 1));
+    let extend_memory = calculate_gas_extend_memory(evm.value.memory, extensions_list);
+    let err = charge_gas(
+        Uint(GasConstants.GAS_VERY_LOW + return_data_copy_gas_cost + extend_memory.value.cost.value)
+    );
+    if (cast(err, felt) != 0) {
+        return err;
+    }
+
+    let memory = evm.value.memory;
+    // Check if the read on return_data is in bounds
+    // If the start position is greater than 2 ** 128, then it is almost surely out of bounds
+    if (returndata_start_position.value.high != 0) {
+        tempvar err = new ExceptionalHalt(OutOfBoundsRead);
+        return err;
+    }
+    // Check if returndata_start_position and size are each less than 2**128, so that their
+    // sum is less than 2**129, which fits into a felt. We can then be sure that
+    // size.value.low + returndata_start_position.value.low won't wrap around the PRIME.
+    assert [range_check_ptr] = returndata_start_position.value.low;
+    let range_check_ptr = range_check_ptr + 1;
+    assert [range_check_ptr] = size.value.low;
+    let range_check_ptr = range_check_ptr + 1;
+    let is_in_bounds = is_le(
+        size.value.low + returndata_start_position.value.low, evm.value.return_data.value.len
+    );
+    if (is_in_bounds == 0) {
+        tempvar err = new ExceptionalHalt(OutOfBoundsRead);
+        return err;
+    }
+
+    with memory {
+        expand_by(extend_memory.value.expand_by);
+        let value = buffer_read(evm.value.return_data, returndata_start_position, size);
+        memory_write(memory_start_index, value);
+    }
+    EvmImpl.set_pc_stack_memory(Uint(evm.value.pc.value + 1), stack, memory);
+    let ok = cast(0, ExceptionalHalt*);
+    return ok;
+}
+
 // @notice Push the balance of the current address to the stack
 func self_balance{range_check_ptr, poseidon_ptr: PoseidonBuiltin*, evm: Evm}() -> ExceptionalHalt* {
     alloc_locals;

cairo/tests/ethereum/cancun/vm/instructions/test_environment.py

@@ -16,6 +16,7 @@
     codesize,
     gasprice,
     origin,
+    returndatacopy,
     returndatasize,
     self_balance,
 )
@@ -56,6 +57,16 @@
     EvmBuilder().with_gas_left().with_env(environment_empty_state).build()
 )
 
+evm_environment_strategy_with_return_data = (
+    EvmBuilder()
+    .with_memory()
+    .with_gas_left()
+    .with_env(environment_empty_state)
+    .with_return_data()
+    .with_capped_values_stack()
+    .build()
+)
+
 code_access_size_strategy = st.integers(min_value=0, max_value=MAX_CODE_SIZE).map(U256)
 code_start_index_strategy = code_access_size_strategy
 
@@ -194,6 +205,18 @@ def test_returndatasize(self, cairo_run, evm: Evm):
         returndatasize(evm)
         assert evm == cairo_result
 
+    @given(evm=evm_environment_strategy_with_return_data)
+    def test_returndatacopy(self, cairo_run, evm: Evm):
+        try:
+            cairo_result = cairo_run("returndatacopy", evm)
+        except Exception as cairo_error:
+            with strict_raises(type(cairo_error)):
+                returndatacopy(evm)
+            return
+
+        returndatacopy(evm)
+        assert evm == cairo_result
+
     @given(evm=evm_environment_strategy)
     def test_self_balance(self, cairo_run, evm: Evm):
         try:

cairo/tests/utils/evm_builder.py

@@ -92,6 +92,14 @@ def with_stack(self, strategy=stack_strategy(Stack[U256])):
         self._stack = strategy
         return self
 
+    def with_capped_values_stack(self, max_value=2**8 - 1):
+        self._stack = st.lists(
+            st.integers(min_value=0, max_value=max_value).map(U256),
+            min_size=0,
+            max_size=1024,
+        ).map(lambda x: Stack[U256](x))
+        return self
+
     def with_memory(self, strategy=memory_lite):
         self._memory = strategy
         return self
@@ -132,6 +140,10 @@ def with_accessed_storage_keys(
         self._accessed_storage_keys = strategy
         return self
 
+    def with_return_data(self, strategy=st.binary(min_size=0, max_size=1024)):
+        self._return_data = strategy
+        return self
+
     def build(self):
         return st.builds(
             Evm,