Add fractional CALLDATA gas cost (ethereum#75)

Since an FHE-based chain could require relatively big FHE ciphertexts to
be passed as transaction inputs, reduce the CALLDATA gas cost to
`1 / TxFheDataFractionalGas` per byte. Currently, it costs 1/4 gas
per byte. It doesn't matter if a byte is zero or non-zero, the cost is
the same. The `TxFheDataFractionalGas` constant could be changed in the
future as we gain more usage patterns from live networks.

core/state_transition.go

@@ -18,7 +18,6 @@ package core
 
 import (
 	"fmt"
-	"math"
 	"math/big"
 
 	"github.com/ethereum/go-ethereum/common"
@@ -42,8 +41,10 @@ The state transitioning model does all the necessary work to work out a valid ne
 3) Create a new state object if the recipient is \0*32
 4) Value transfer
 == If contract creation ==
-  4a) Attempt to run transaction data
-  4b) If valid, use result as code for the new state object
+
+	4a) Attempt to run transaction data
+	4b) If valid, use result as code for the new state object
+
 == end ==
 5) Run Script section
 6) Derive new state root
@@ -125,28 +126,9 @@ func IntrinsicGas(data []byte, accessList types.AccessList, isContractCreation b
 	}
 	// Bump the required gas by the amount of transactional data
 	if len(data) > 0 {
-		// Zero and non-zero bytes are priced differently
-		var nz uint64
-		for _, byt := range data {
-			if byt != 0 {
-				nz++
-			}
-		}
-		// Make sure we don't exceed uint64 for all data combinations
-		nonZeroGas := params.TxDataNonZeroGasFrontier
-		if isEIP2028 {
-			nonZeroGas = params.TxDataNonZeroGasEIP2028
-		}
-		if (math.MaxUint64-gas)/nonZeroGas < nz {
-			return 0, ErrGasUintOverflow
-		}
-		gas += nz * nonZeroGas
-
-		z := uint64(len(data)) - nz
-		if (math.MaxUint64-gas)/params.TxDataZeroGas < z {
-			return 0, ErrGasUintOverflow
-		}
-		gas += z * params.TxDataZeroGas
+		// We ignore EIP 20228 here. Rationale is that current gas cost calculation is very different.
+		// Please consult EIP 2028 for more information, especially if the current gas calculation is problematic.
+		gas += uint64(len(data)) / params.TxFheDataFractionalGas
 	}
 	if accessList != nil {
 		gas += uint64(len(accessList)) * params.TxAccessListAddressGas
@@ -262,13 +244,13 @@ func (st *StateTransition) preCheck() error {
 // TransitionDb will transition the state by applying the current message and
 // returning the evm execution result with following fields.
 //
-// - used gas:
-//      total gas used (including gas being refunded)
-// - returndata:
-//      the returned data from evm
-// - concrete execution error:
-//      various **EVM** error which aborts the execution,
-//      e.g. ErrOutOfGas, ErrExecutionReverted
+//   - used gas:
+//     total gas used (including gas being refunded)
+//   - returndata:
+//     the returned data from evm
+//   - concrete execution error:
+//     various **EVM** error which aborts the execution,
+//     e.g. ErrOutOfGas, ErrExecutionReverted
 //
 // However if any consensus issue encountered, return the error directly with
 // nil evm execution result.

params/protocol_params.go

@@ -86,6 +86,7 @@ const (
 
 	TxDataNonZeroGasFrontier  uint64 = 68   // Per byte of data attached to a transaction that is not equal to zero. NOTE: Not payable on data of calls between transactions.
 	TxDataNonZeroGasEIP2028   uint64 = 16   // Per byte of non zero data attached to a transaction after EIP 2028 (part in Istanbul)
+	TxFheDataFractionalGas    uint64 = 4    // A byte of data attached to a transaction has fractional cost: 1 / TxFheDataFractionGas (part of an FHE-based chain)
 	TxAccessListAddressGas    uint64 = 2400 // Per address specified in EIP 2930 access list
 	TxAccessListStorageKeyGas uint64 = 1900 // Per storage key specified in EIP 2930 access list