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contract ThisExternalAssembly {
uint8 public numcalls;
uint8 public numcallsinternal;
uint8 public numfails;
uint8 public numsuccesses;
address owner;
event logCall(uint8 indexed _numcalls, uint8 indexed _numcallsinternal);
modifier onlyOwner { if (msg.sender != owner) throw; _ }
modifier onlyThis { if (msg.sender != address(this)) throw; _ }
// constructor
function ThisExternalAssembly() {
owner = msg.sender;
}
function failSend() external onlyThis returns (bool) {
// storage change + nested external call
numcallsinternal++;
owner.send(42);
// placeholder for state checks
if (true) throw;
// never happens in this case
return true;
}
function doCall(uint _gas) onlyOwner {
numcalls++;
address addr = address(this);
bytes4 sig = bytes4(sha3("failSend()"));
bool ret;
// work around `solc` safeguards for throws in external calls
// https://ethereum.stackexchange.com/questions/6354/
assembly {
let x := mload(0x40) // read "empty memory" pointer
mstore(x,sig)
ret := call(
_gas, // gas amount
addr, // recipient account
0, // value (no need to pass)
x, // input start location
0x4, // input size - just the sig
x, // output start location
0x1) // output size (bool - 1 byte)
//ret := mload(x) // no return value ever written :/
mstore(0x40,add(x,0x4)) // just in case, roll the tape
}
if (ret) { numsuccesses++; }
else { numfails++; }
// mostly helps with function identification if disassembled
logCall(numcalls, numcallsinternal);
}
// will clean-up :)
function selfDestruct() onlyOwner { selfdestruct(owner); }
function() { throw; }
}