Gas

Each instruction executed in TVM consumes gas. All instructions consume basic gas, which is calculated from the size of the instruction in the bitcode. Some instructions may consume extra gas, which is often not fixed but calculated based on the input data.

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Basic gas usage (per bit of executed code)

Each instruction consumes a fixed amount of 10 gas and 1 gas for each bit of this instruction, not including variable-length operands and references. Examples:

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Cell operations

When any instruction internally finalizes a Builder to a Cell, it consumes 500 gas. When a Cell is loaded as a Slice, it consumes 100 gas for the first access in current smart contract invocation, and 25 gas for each subsequent load from cache. Cells are identified by representation hash, e.g., loading cell with the same hash for the second time will always cost 25 gas. This applies to all instructions that internally operate with cells (including dictionary operations). The only exceptions are:

• BTOS converts a Builder to a Slice without consuming gas for cell operations.
• HASHBU computes hash without consuming gas for converting Builder to a Cell

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Exceptions

TVM consumes 50 gas when any exception is thrown, both explicitly by THROW-like instructions or implicitly during execution of other instructions. This happens before the jump to the exception handler c2.

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Implicit jumps and returns

When the current continuation ends and there is a remaining reference, TVM jumps to it and consumes 10 gas. When there are no instructions to execute and references to jump to, implicit return to c0 occurs, which consumes 5 gas.

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Nested continuations

Calling more than 8 extraordinary continuations in a chain consumes 1 gas for each subsequent continuation.

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Tuple operations

TUPLE, TUPLEVAR, UNTUPLE, UNTUPLEVAR, UNPACKFIRST, UNPACKFIRSTVAR, EXPLODE, EXPLODEVAR consumes 1 gas for each entry been pushed or popped into a tuple. TPUSH, TPOP, SETINDEX, SETINDEXVAR, SETINDEXQ/SETINDEXVARQ consumes len(tuple) gas for the resulting tuple size after push/pop/set. Same applies to instructions operating with c7: SETGLOB/SETGLOBVAR, RANDU256/RAND, SETRAND, ADDRAND.

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Stack operations

TVM consumes 1 gas for each stack element deeper than 32 elements inside the resulting new stack each time stack gets copied: when calling or jumping to a continuation with a non-empty argument number, an initial stack, or both, when extending a continuation stack using SETCONTARGS and similar instructions, when using RUNVM (both for initial and resulting stacks of the vm).

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Extra currency

The first 5 executions of GETEXTRABALANCE consume at most 26 + 200 gas each. The subsequent executions incur the full gas cost of 26 (normal instruction cost) plus gas for loading cells (up to 3300 if the dictionary has maximum depth).

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RUNVM

RUNVM and RUNVMX consume 40 extra gas before starting a VM.

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Cryptography

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CHKSIGNS/CHKSIGNU

CHKSIGNS and CHKSIGNU can be invoked 10 times without extra gas cost. Next checks will cost 4000 gas each.

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HASHEXT

HASHEXT* instructions always consume 1 extra gas for each part of the input. Additionally, the following gas is consumed for each hashed byte: Only the integer part of the gas is consumed; for example, 0-32 bytes of SHA256 cost 0 gas, 33-64 bytes cost 1 gas, and so on.

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RIST255

Instructions consume constant extra gas.

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Other instructions

ECRECOVER consumes 1500 extra gas. SECP256K1_XONLY_PUBKEY_TWEAK_ADD consumes 1250 extra gas. P256_CHKSIGNU and P256_CHKSIGNS consume 3500 extra gas.

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BLS

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Signature verification and aggregation

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G1 group helpers

BLS_G1_MULTIEXP consumes 11375 + 630 * n + (8820 * n) / max(log₂ n, 4) extra gas, where n is the number of (point, scalar) pairs. Instructions BLS_G1_ZERO and BLS_G1_ISZERO do not charge additional gas.

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G2 group helpers

BLS_G2_MULTIEXP consumes 30388 + 1280 * n + (22840 * n) / max(log₂ n, 4) gas, where n is the number of (point, scalar) pairs. Instructions BLS_G2_ZERO and BLS_G2_ISZERO do not charge additional gas.

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Pairing and constants

BLS_PUSHR do not charge additional gas.

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GasLimits structure

TVM has inner structure GasLimits for gas manipulations. Its fields are:

• gas_max: the equivalent of contract’s balance at the start of the compute phase in gas units.
• gas_limit: the amount of gas that can be consumed during the virtual machine execution. At the start of the execution, it equals:
  • minimum of gas_max and the amount of gas that can be bought with the incoming message value (i.e., the amount of TON coins attached to the message) in the case of an internal message;
  • 0 in the case of an external message.
• gas_credit: the amount of free gas that can be spent during the execution before accepting an external message. At the start of the execution, it equals:
  • minimum of gas_max and corresponding value in configuration parameter 20 for masterchain and 21 for basechain in the case of an external message;
  • 0 in the case of an internal message.
• gas_remaining: the amount of available but not spent gas. At the start of the execution, it equals gas_limit + gas_credit. It decreases after each instruction execution by the amount of gas consumed by the instruction.
• gas_base: an auxiliary parameter that is necessary for rebasing and shows the initial value of gas_remaining. At the start of the execution, it equals gas_remaining.

Instructions SETGASLIMIT and ACCEPT change all above values except gas_max:

• SETGASLIMIT sets gas_limit to the minimum of the indicated value and gas_max, gas_credit to zero, gas_base to the new gas_limit, and gas_remaining to gas_remaining + (new gas_base - old gas_base).
• ACCEPT is equivalent to SETGASLIMIT with the new gas limit equal to 2**63 - 1 (the maximum value of a signed 64-bits integer).

The final value (in gas units) that will be deducted from contract’s balance after the execution is gas_base - gas_remaining. Note that this value will be deducted if and only if after the execution gas_credit is zero, i.e. if SETGASLIMIT or ACCEPT was called at least once during the execution in the case of incoming external message. Without condition gas_credit == 0, there will be no commit of the new code and data.