HPB Gas 机制
导读：本文档基于hpb-1.0.2.3 版本，由于在涉及到转账交易和智能合约运算时，都会涉及到Gas费用问题，这篇文章我们主要介绍HPB的Gas 机制。
首先 1 HPB = 1,000,000,000,000,000,000 Wei 就是 1^18， 1 Gwei = 1,000,000,000 Wei。
交易费用 = Gas * Gas Price.
HPB 计量单位转换关系
| 单位 | Wei | Kwei | babbage | femtohpb | mwei | lovelace | picohpb |
|---|---|---|---|---|---|---|---|
| Wei | 1 | 103 | 103 | 103 | 106 | 106 | 106 |
| 单位 | gwei | shannon | nanohpb | nano | szabo | microhpb | micro |
| Wei | 109 | 109 | 109 | 109 | 1012 | 1012 | 1012 |
| 单位 | finney | millihpb | milli | hpb | khpb | grand | mhpb |
| Wei | 1015 | 1015 | 1015 | 1018 | 1021 | 1021 | 1024 |
| 单位 | ghpb | thpb | phpb | ehpb | zhpb | yhpb | nhpb |
| Wei | 1027 | 1030 | 1033 | 1036 | 1039 | 1042 | 1045 |
| 单位 | dhpb | vhpb | uhpb | ||||
| Wei | 1048 | 1051 | 1054 |
Gas如何收取
无智能合约的普通交易
在HPB主网里，交易费用在涉及普通交易和智能合约交易时并不相同，通常来说HPB普通交易的默认Gas Units = 10. Gas price 根据HPB所有节点的竞争而变化，在此版本的源代码里默认是大于1Wei，现实环境中，经验值为 Gas Price = 18Gwei.
智能合约创建交易
基本费用： 默认Gas Units = 53000.
数据费用：交易的data字段，每个字节1个
合约预编译费用：根据预编译函数返回结果，预编译函数评估时，不同的指令集，收取Gas的方法不同。简单指令（如Add，MUL，AND，OR等）收取固定Gas，复杂指令（如内存操作MLOAD，SLOAD）根据使用的内存进行收取。
智能合约运行交易
基本费用： 默认Gas Units = 10.
数据费用：交易的data字段，每个字节1个.
合约预编译费用：根据所调用智能合约类型的不同，Gas计算方法不同，请参照HPB 源代码，如下所示：
// Precompiled contract gas prices
EcrecoverGas uint64 = 3000 // Elliptic curve sender recovery gas price
Sha256BaseGas uint64 = 60 // Base price for a SHA256 operation
Sha256PerWordGas uint64 = 12 // Per-word price for a SHA256 operation
Ripemd160BaseGas uint64 = 600 // Base price for a RIPEMD160 operation
Ripemd160PerWordGas uint64 = 120 // Per-word price for a RIPEMD160 operation
IdentityBaseGas uint64 = 15 // Base price for a data copy operation
IdentityPerWordGas uint64 = 3 // Per-work price for a data copy operation
ModExpQuadCoeffDiv uint64 = 20 // Divisor for the quadratic particle of the big int modular exponentiation
Bn256AddGas uint64 = 500 // Gas needed for an elliptic curve addition
Bn256ScalarMulGas uint64 = 40000 // Gas needed for an elliptic curve scalar multiplication
Bn256PairingBaseGas uint64 = 100000 // Base price for an elliptic curve pairing check
Bn256PairingPerPointGas uint64 = 80000 // Per-point price for an elliptic curve pairing check
const (
MaximumExtraDataSize uint64 = 32 // Maximum size extra data may be after Genesis.
ExpByteGas uint64 = 10 // Times ceil(log256(exponent)) for the EXP instruction.
SloadGas uint64 = 50 // Multiplied by the number of 32-byte words that are copied (round up) for any *COPY operation and added.
CallValueTransferGas uint64 = 9000 // Paid for CALL when the value transfer is non-zero.
CallNewAccountGas uint64 = 25000 // Paid for CALL when the destination address didn't exist prior.
TxGas uint64 = 10 // Per transaction not creating a contract. NOTE: Not payable on data of calls between transactions. //for testnet
TxGasContractCreation uint64 = 53000 // Per transaction that creates a contract. NOTE: Not payable on data of calls between transactions.
TxDataZeroGas uint64 = 1 // Per byte of data attached to a transaction that equals zero. NOTE: Not payable on data of calls between transactions. //for testnet
QuadCoeffDiv uint64 = 512 // Divisor for the quadratic particle of the memory cost equation.
SstoreSetGas uint64 = 20000 // Once per SLOAD operation.
LogDataGas uint64 = 8 // Per byte in a LOG* operation's data.
CallStipend uint64 = 2300 // Free gas given at beginning of call.
Sha3Gas uint64 = 30 // Once per SHA3 operation.
Sha3WordGas uint64 = 6 // Once per word of the SHA3 operation's data.
SstoreResetGas uint64 = 5000 // Once per SSTORE operation if the zeroness changes from zero.
SstoreClearGas uint64 = 5000 // Once per SSTORE operation if the zeroness doesn't change.
SstoreRefundGas uint64 = 15000 // Once per SSTORE operation if the zeroness changes to zero.
JumpdestGas uint64 = 1 // Refunded gas, once per SSTORE operation if the zeroness changes to zero.
EpochDuration uint64 = 30000 // Duration between proof-of-work epochs.
CallGas uint64 = 40 // Once per CALL operation & message call transaction.
CreateDataGas uint64 = 200 //
CallCreateDepth uint64 = 1024 // Maximum depth of call/create stack.
ExpGas uint64 = 10 // Once per EXP instruction
LogGas uint64 = 375 // Per LOG* operation.
CopyGas uint64 = 3 //
StackLimit uint64 = 1024 // Maximum size of VM stack allowed.
TierStepGas uint64 = 0 // Once per operation, for a selection of them.
LogTopicGas uint64 = 375 // Multiplied by the * of the LOG*, per LOG transaction. e.g. LOG0 incurs 0 * c_txLogTopicGas, LOG4 incurs 4 * c_txLogTopicGas.
CreateGas uint64 = 32000 // Once per CREATE operation & contract-creation transaction.
SuicideRefundGas uint64 = 24000 // Refunded following a suicide operation.
MemoryGas uint64 = 3 // Times the address of the (highest referenced byte in memory + 1). NOTE: referencing happens on read, write and in instructions such as RETURN and CALL.
TxDataNonZeroGas uint64 = 1 // Per byte of data attached to a transaction that is not equal to zero. NOTE: Not payable on data of calls between transactions. //for testnet
MaxCodeSize = 24576 // Maximum bytecode to permit for a contract
Gas Price说明
在我们常见的ETH钱包中Gas Price在不同阶段是会有调整，通常来说都是钱包根据网络情况为用户设置，HPB Wallet 也 默认帮助用户设置Gas Price，此版本源代码默认是只要大于1Wei即可以，现阶段的经验值为18Gwei，同样HPB智能合约的Gas Price也遵循同样的机制，现阶段运行智能合约的Gas Price 为 18Gwei。
FAQ
Q1: Gas 如何计算？
A1: 请参照上表中的计算方式.
Q2:一个交易最少消耗多少交易费用？
A2: 首先要确定属于哪一种交易，普通交易还是智能合约交易，然后根据上表中Gas的规定去计算，交易费用=Gas * Gas Price，例如普通交易的Gas为固定值 10 ，没有最大和最小之分，智能合约部分也请参照上面的表去计算，每一种交易都有一个最低的Gas 要求，另外交易费用是手动可设置的，例如用户想交易更快，可以调节参数Gas Price的值。
Q3: 普通交易最多消耗多少Gas？
A3: 普通交易的Gas是固定值 10 .
Q4:智能合约交易最多消耗多少Gas？
A4:智能合约的Gas没有上限 .
Q5: 搭建Dapp需要购买HPB token才能搭建到HPB主网上吗？
A4: Yes.
Q6:Dapp搭建是否需要锁定HPB Token？
A6: 目前的版本不需要锁定，只是在部署过程中和运行中需要一定的交易费用.
Q7:Dapp是否可以搭建在测试平台？
A7: 可以，测试链平台有智能合约功能，现在最新的测试链还没有完全释放出来给社区用，待准备好之后再提供给社区的爱好者使用，同时提供测试链的token。
Q8:交易费用如何分配？
A8:交易费用会奖励给维护HPB主网的出块节点.
Q9:智能合约最少消耗多少交易费用？
A9: 智能合约的交易费用请参考上表中的数字计算，交易费用 = Gas * Gas Price.
另外关于交易费用，请根据公式计算 ，举个例子： 以当前Gas Price = 18Gwei 为例，普通合约运行交易交易费用 = 10 18Gwei，创建智能合约的最低交易费用= 53000 18Gwei，执行智能合约的最低交易费用 = 10 * 18Gwei.