1 files changed, 53 insertions, 0 deletions
diff --git a/core/vm/gas.go b/core/vm/gas.go
new file mode 100644
index 0000000..bd8b4f1
--- /dev/null
+++ b/core/vm/gas.go
@@ -0,0 +1,53 @@
+// Copyright 2015 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package vm
+
+import (
+	"math/big"
+)
+
+// Gas costs
+const (
+	GasQuickStep   uint64 = 2
+	GasFastestStep uint64 = 3
+	GasFastStep    uint64 = 5
+	GasMidStep     uint64 = 8
+	GasSlowStep    uint64 = 10
+	GasExtStep     uint64 = 20
+)
+
+// calcGas returns the actual gas cost of the call.
+//
+// The cost of gas was changed during the homestead price change HF.
+// As part of EIP 150 (TangerineWhistle), the returned gas is gas - base * 63 / 64.
+func callGas(isEip150 bool, availableGas, base uint64, callCost *big.Int) (uint64, error) {
+	if isEip150 {
+		availableGas = availableGas - base
+		gas := availableGas - availableGas/64
+		// If the bit length exceeds 64 bit we know that the newly calculated "gas" for EIP150
+		// is smaller than the requested amount. Therefor we return the new gas instead
+		// of returning an error.
+		if !callCost.IsUint64() || gas < callCost.Uint64() {
+			return gas, nil
+		}
+	}
+	if !callCost.IsUint64() {
+		return 0, errGasUintOverflow
+	}
+
+	return callCost.Uint64(), nil
+}