escape inifinite loop in estimte_gas

ethcore/src/client/client.rs

@@ -1231,12 +1231,12 @@ impl BlockChainClient for Client {
 	}
 
 	fn estimate_gas(&self, t: &SignedTransaction, block: BlockId) -> Result<U256, CallError> {
-		const UPPER_CEILING: u64 = 1_000_000_000_000u64;
-		let (mut upper, env_info)  = {
+		let (mut upper, max_upper, env_info)  = {
 			let mut env_info = self.env_info(block).ok_or(CallError::StatePruned)?;
-			let initial_upper = env_info.gas_limit;
-			env_info.gas_limit = UPPER_CEILING.into();
-			(initial_upper, env_info)
+			let init = env_info.gas_limit;
+			let max = init * U256::from(10);
+			env_info.gas_limit = max;
+			(init, max, env_info)
 		};
 
 		// that's just a copy of the state.
@@ -1257,9 +1257,7 @@ impl BlockChainClient for Client {
 		};
 
 		if !cond(upper)? {
-			// impossible at block gas limit - try `UPPER_CEILING` instead.
-			// TODO: consider raising limit by powers of two.
-			upper = UPPER_CEILING.into();
+			upper = max_upper;
 			if !cond(upper)? {
 				trace!(target: "estimate_gas", "estimate_gas failed with {}", upper);
 				let err = ExecutionError::Internal(format!("Requires higher than upper limit of {}", upper));