Method popStorageArrayElement

libsolidity/codegen/ArrayUtils.cpp:493–579

}

void ArrayUtils::popStorageArrayElement(ArrayType const& _type) const
{
	solAssert(_type.location() == DataLocation::Storage, "");
	solAssert(_type.isDynamicallySized(), "");
	if (!_type.isByteArrayOrString() && _type.baseType()->storageBytes() < 32)
		solAssert(_type.baseType()->isValueType(), "Invalid storage size for non-value type.");

	if (_type.isByteArrayOrString())
	{
		m_context << Instruction::DUP1 << Instruction::SLOAD << Instruction::DUP1;
		m_context.callYulFunction(m_context.utilFunctions().extractByteArrayLengthFunction(), 1, 1);
		util::Whiskers code(R"({
			if iszero(length) {
				mstore(0, <panicSelector>)
				mstore(4, <emptyArrayPop>)
				revert(0, 0x24)
			}
			switch gt(length, 31)
			case 0 {
				// short byte array
				// Zero-out the suffix including the least significant byte.
				let mask := sub(exp(0x100, sub(33, length)), 1)
				length := sub(length, 1)
				slot_value := or(and(not(mask), slot_value), mul(length, 2))
			}
			case 1 {
				// long byte array
				mstore(0, ref)
				let slot := keccak256(0, 0x20)
				switch length
				case 32
				{
					let data := sload(slot)
					sstore(slot, 0)
					data := and(data, not(0xff))
					slot_value := or(data, 62)
				}
				default
				{
					let offset_inside_slot := and(sub(length, 1), 0x1f)
					slot := add(slot, div(sub(length, 1), 32))
					let data := sload(slot)

					// Zero-out the suffix of the byte array by masking it.
					// ((1<<(8 * (32 - offset))) - 1)
					let mask := sub(exp(0x100, sub(32, offset_inside_slot)), 1)
					data := and(not(mask), data)
					sstore(slot, data)

					// Reduce the length by 1
					slot_value := sub(slot_value, 2)
				}
			}
			sstore(ref, slot_value)
		})");
		code("panicSelector", util::selectorFromSignatureU256("Panic(uint256)").str());
		code("emptyArrayPop", std::to_string(unsigned(util::PanicCode::EmptyArrayPop)));
		m_context.appendInlineAssembly(code.render(), {"ref", "slot_value", "length"});