Add SHR Opcode for Constantinople

Author: cburgdorf

eth/vm/forks/constantinople/opcodes.py

@@ -27,6 +27,11 @@
         mnemonic=mnemonics.SHL,
         gas_cost=constants.GAS_VERYLOW,
     ),
+    opcode_values.SHR: as_opcode(
+        logic_fn=arithmetic.shr,
+        mnemonic=mnemonics.SHR,
+        gas_cost=constants.GAS_VERYLOW,
+    ),
 }
 
 CONSTANTINOPLE_OPCODES = merge(

eth/vm/logic/arithmetic.py

@@ -191,3 +191,17 @@ def shl(computation):
         result = (value << shift_length) & constants.UINT_256_MAX
 
     computation.stack_push(result)
+
+
+def shr(computation):
+    """
+    Bitwise right shift
+    """
+    shift_length, value = computation.stack_pop(num_items=2, type_hint=constants.UINT256)
+
+    if shift_length >= 256:
+        result = 0
+    else:
+        result = (value >> shift_length) & constants.UINT_256_MAX
+
+    computation.stack_push(result)

eth/vm/mnemonics.py

@@ -14,6 +14,7 @@
 EXP = 'EXP'
 SIGNEXTEND = 'SIGNEXTEND'
 SHL = 'SHL'
+SHR = 'SHR'
 #
 # Comparisons
 #

eth/vm/opcode_values.py

@@ -30,6 +30,7 @@
 NOT = 0x19
 BYTE = 0x1a
 SHL = 0x1b
+SHR = 0x1c
 
 
 #

tests/core/opcodes/test_opcodes.py

@@ -183,3 +183,85 @@ def test_shl(vm_class, val1, val2, expected):
     result = computation.stack_pop(type_hint=constants.UINT256)
 
     assert encode_hex(pad32(int_to_big_endian(result))) == expected
+
+
+@pytest.mark.parametrize(
+    # Cases: https://github.com/ethereum/EIPs/blob/master/EIPS/eip-145.md#shr-logical-shift-right
+    'vm_class, val1, val2, expected',
+    (
+        (
+            ConstantinopleVM,
+            '0x0000000000000000000000000000000000000000000000000000000000000001',
+            '0x00',
+            '0x0000000000000000000000000000000000000000000000000000000000000001',
+        ),
+        (
+            ConstantinopleVM,
+            '0x0000000000000000000000000000000000000000000000000000000000000001',
+            '0x01',
+            '0x0000000000000000000000000000000000000000000000000000000000000000',
+        ),
+        (
+            ConstantinopleVM,
+            '0x8000000000000000000000000000000000000000000000000000000000000000',
+            '0x01',
+            '0x4000000000000000000000000000000000000000000000000000000000000000',
+        ),
+        (
+            ConstantinopleVM,
+            '0x8000000000000000000000000000000000000000000000000000000000000000',
+            '0xff',
+            '0x0000000000000000000000000000000000000000000000000000000000000001',
+        ),
+        (
+            ConstantinopleVM,
+            '0x8000000000000000000000000000000000000000000000000000000000000000',
+            '0x0100',
+            '0x0000000000000000000000000000000000000000000000000000000000000000',
+        ),
+        (
+            ConstantinopleVM,
+            '0x8000000000000000000000000000000000000000000000000000000000000000',
+            '0x0101',
+            '0x0000000000000000000000000000000000000000000000000000000000000000',
+        ),
+        (
+            ConstantinopleVM,
+            '0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff',
+            '0x00',
+            '0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff',
+        ),
+        (
+            ConstantinopleVM,
+            '0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff',
+            '0x01',
+            '0x7fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff',
+        ),
+        (
+            ConstantinopleVM,
+            '0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff',
+            '0xff',
+            '0x0000000000000000000000000000000000000000000000000000000000000001',
+        ),
+        (
+            ConstantinopleVM,
+            '0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff',
+            '0x0100',
+            '0x0000000000000000000000000000000000000000000000000000000000000000',
+        ),
+        (
+            ConstantinopleVM,
+            '0x0000000000000000000000000000000000000000000000000000000000000000',
+            '0x01',
+            '0x0000000000000000000000000000000000000000000000000000000000000000',
+        ),
+    )
+)
+def test_shr(vm_class, val1, val2, expected):
+    computation = prepare_computation(vm_class)
+    computation.stack_push(decode_hex(val1))
+    computation.stack_push(decode_hex(val2))
+    computation.opcodes[opcode_values.SHR](computation)
+
+    result = computation.stack_pop(type_hint=constants.UINT256)
+    assert encode_hex(pad32(int_to_big_endian(result))) == expected