diff options
Diffstat (limited to 'libevmasm/ConstantOptimiser.cpp')
| -rw-r--r-- | libevmasm/ConstantOptimiser.cpp | 57 |
1 files changed, 55 insertions, 2 deletions
diff --git a/libevmasm/ConstantOptimiser.cpp b/libevmasm/ConstantOptimiser.cpp index a1dfd21c..0c093ebf 100644 --- a/libevmasm/ConstantOptimiser.cpp +++ b/libevmasm/ConstantOptimiser.cpp @@ -203,8 +203,13 @@ AssemblyItems ComputeMethod::findRepresentation(u256 const& _value) u256 powerOfTwo = u256(1) << bits; u256 upperPart = _value >> bits; bigint lowerPart = _value & (powerOfTwo - 1); - if (abs(powerOfTwo - lowerPart) < lowerPart) + if ((powerOfTwo - lowerPart) < lowerPart) + { lowerPart = lowerPart - powerOfTwo; // make it negative + upperPart++; + } + if (upperPart == 0) + continue; if (abs(lowerPart) >= (powerOfTwo >> 8)) continue; @@ -212,7 +217,7 @@ AssemblyItems ComputeMethod::findRepresentation(u256 const& _value) if (lowerPart != 0) newRoutine += findRepresentation(u256(abs(lowerPart))); newRoutine += AssemblyItems{u256(bits), u256(2), Instruction::EXP}; - if (upperPart != 1 && upperPart != 0) + if (upperPart != 1) newRoutine += findRepresentation(upperPart) + AssemblyItems{Instruction::MUL}; if (lowerPart > 0) newRoutine += AssemblyItems{Instruction::ADD}; @@ -232,6 +237,54 @@ AssemblyItems ComputeMethod::findRepresentation(u256 const& _value) } } +bool ComputeMethod::checkRepresentation(u256 const& _value, AssemblyItems const& _routine) +{ + // This is a tiny EVM that can only evaluate some instructions. + vector<u256> stack; + for (AssemblyItem const& item: _routine) + { + switch (item.type()) + { + case Operation: + { + if (stack.size() < size_t(item.arguments())) + return false; + u256* sp = &stack.back(); + switch (item.instruction()) + { + case Instruction::MUL: + sp[-1] = sp[0] * sp[-1]; + break; + case Instruction::EXP: + if (sp[-1] > 0xff) + return false; + sp[-1] = boost::multiprecision::pow(sp[0], unsigned(sp[-1])); + break; + case Instruction::ADD: + sp[-1] = sp[0] + sp[-1]; + break; + case Instruction::SUB: + sp[-1] = sp[0] - sp[-1]; + break; + case Instruction::NOT: + sp[0] = ~sp[0]; + break; + default: + return false; + } + stack.resize(stack.size() + item.deposit()); + break; + } + case Push: + stack.push_back(item.data()); + break; + default: + return false; + } + } + return stack.size() == 1 && stack.front() == _value; +} + bigint ComputeMethod::gasNeeded(AssemblyItems const& _routine) { size_t numExps = count(_routine.begin(), _routine.end(), Instruction::EXP); |