Gas Accounting
The embedded runtime tracks gas consumption to approximate production Neo N3 behavior.
How Gas Works
Every opcode and syscall has an associated gas cost. The runtime deducts gas before executing each instruction. If gas reaches zero, execution halts with an out-of-gas error.
Opcode Gas Costs
Gas costs by opcode category:
| Category | Typical Gas | Notes |
|---|---|---|
| Constants (PUSH*) | 1-2 | PUSHDATA variants cost 2 |
| Flow control (JMP*) | 2 | CALL variants cost 512 |
| Stack operations | 2 | All stack manipulation |
| Slot operations | 2-3 | INITSLOT costs 3 |
| Splice/buffer | 4 | All buffer operations |
| Bitwise/logic | 2-3 | |
| Numeric (basic) | 3 | ADD, SUB, comparisons |
| Numeric (complex) | 5-8 | MUL, DIV, POW, MODPOW |
| Collections | 4 | All compound operations |
| Type operations | 2 | ISNULL, ISTYPE, CONVERT |
| RET | 0 | Free |
Syscall Gas Costs
| Syscall Category | Gas Cost | Notes |
|---|---|---|
| Storage context (GetContext, AsReadOnly) | 1 | Cheap metadata operations |
| Storage read (Get, Find) | 100 | Per-operation |
| Storage write (Put) | 1,000 | Most expensive common operation |
| Storage delete (Delete) | 100 | |
| Iterator (Next, Value) | 1 | |
| Runtime metadata (Platform, GetTime, etc.) | 1 | |
| Runtime.CheckWitness | 200 | Signature verification |
| Runtime.GetRandom | 50 | |
| Runtime.Log / Notify | 1 | |
| Crypto.CheckSig / CheckMultisig | 1,000 | Cryptographic verification |
| Contract.Call | 10 | |
| Contract.Create*Account | 10 |
Current Accuracy
Gas accounting is an embedded-runtime approximation of production Neo N3 costs. Known gaps:
- Dynamic costs for large integer operations are approximated
- Some complex operations use fixed costs instead of size-dependent costs
- Edge cases in exception handling gas effects need spec verification
TIP
For precise gas estimation, deploy to Neo-Express or TestNet and measure actual consumption. The embedded runtime is useful for development feedback but should not be used as the sole source of gas budgeting for mainnet.