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eth/vm/logic/arithmetic: handle exp(X,0) == 1. #1217

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Aug 28, 2018
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eth/vm/logic/arithmetic: handle exp(X,0) == 1. #1217

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eth/vm/logic/arithmetic: handle exp(X,0) == 1.
veox Aug 28, 2018
e7b0af9
tests/opcodes: exponentiation: 0^0==1, 0^1==0.
veox Aug 28, 2018
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4 changes: 3 additions & 1 deletion eth/vm/logic/arithmetic.py
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Original file line number Diff line number Diff line change
Expand Up @@ -147,7 +147,9 @@ def exp(computation, gas_per_byte):
bit_size = exponent.bit_length()
byte_size = ceil8(bit_size) // 8

if base == 0:
if exponent == 0:
result = 1
elif base == 0:
result = 0
else:
result = pow(base, exponent, constants.UINT_256_CEILING)
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26 changes: 26 additions & 0 deletions tests/core/opcodes/test_opcodes.py
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Expand Up @@ -123,6 +123,32 @@ def test_mul(vm_class, val1, val2, expected):
assert result == expected


@pytest.mark.parametrize(
'vm_class, base, exponent, expected',
(
(ByzantiumVM, 0, 1, 0,),
(ByzantiumVM, 0, 0, 1,),
(SpuriousDragonVM, 0, 1, 0,),
(SpuriousDragonVM, 0, 0, 1,),
(TangerineWhistleVM, 0, 1, 0,),
(TangerineWhistleVM, 0, 0, 1,),
(HomesteadVM, 0, 1, 0,),
(HomesteadVM, 0, 0, 1,),
(FrontierVM, 0, 1, 0,),
(FrontierVM, 0, 0, 1,),
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Side note: looks like it would be valuable to have a parametrized fixture in conftest that returns all mainnet VMs. Then this would reduce to two cases, and we wouldn't have to remember to update the test on every new fork, like:

@pytest.mark.parametrize(
    'base, exponent, expected',
    (
        (0, 1, 0,),
        (0, 0, 1,),
    )
)
def test_exp(mainnet_vm, base, exponent, expected):
    computation = prepare_computation(mainnet_vm)
    computation.stack_push(exponent)
    computation.stack_push(base)
    computation.opcodes[opcode_values.EXP](computation)
    result = computation.stack_pop(type_hint=constants.UINT256)
    assert result == expected

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Lets wait for the chain-builder to land as it will make this a lot easier to do

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@pipermerriam pipermerriam Aug 30, 2018 •
edited
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chain builder has landed so this should be pretty easy now

)
)
def test_exp(vm_class, base, exponent, expected):
computation = prepare_computation(vm_class)
computation.stack_push(exponent)
computation.stack_push(base)
computation.opcodes[opcode_values.EXP](computation)

result = computation.stack_pop(type_hint=constants.UINT256)

assert result == expected


@pytest.mark.parametrize(
# Testcases from https://github.com/ethereum/EIPs/blob/master/EIPS/eip-145.md#shl-shift-left
'vm_class, val1, val2, expected',
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