# Protocol 006_PsCARTHA Carthage¶

This page contains all the relevant information for protocol 006 Carthage. Each of the main changes is briefly described with links to relevant external documentation and merge requests. There are dedicated sections for all the changes to RPCs and operations. The changelog section contains the most significant commit messages and instructions to regenerate the protocol sources from the Gitlab branch.

Test network Carthagenet is available to test Carthage. See details in Test Networks and instructions to join in How to get Tezos.

The code can be found in the Gitlab branch proto-006 and its full hash is PsCARTHAGazKbHtnKfLzQg3kms52kSRpgnDY982a9oYsSXRLQEb.

This protocol contains several breaking changes with respect to Babylon. Developers are particularly encouraged to carefully read this page and to monitor it for updates.

## Baking Daemon¶

The baking daemon requires direct access to the context of the Tezos node. The daemon for 006 requires the new context introduced by Irmin2. As such bakers that use the default baker need to upgrade to the new storage backend in order to be able to run the 006 baking daemons.

## Smart Contracts¶

The gas limit per block and per operation was increased by 30%. For operations it changed from 800,000 to 1,040,000 and for blocks it changed from 8,000,000 to 10,400,000.

## Baking and Endorsing¶

The formula to calculate baking and endorsing rewards was improved in order to provide more accurate results.

The formula was further modified in order to make it more resistant to certain types of attacks. A full explanation can be found here.

## Accounts¶

The assert that was triggered when a delegated account tried to empty itself was replaced by a proper error message.

## Michelson¶

Protocol 006 contains several improvements to the Michelson smart contract language.

### Optimisation of the CONTRACT instruction¶

The CONTRACT instruction has been optimized to avoid performing a useless disk access in the case its argument is the address of an implicit (aka. tz) account. In this case, this small optimisation saves 132 gas units.

### Comparable pairs in sets and maps¶

Comparability of pairs was added in the Babylon protocol; it is possible in Babylon to use the COMPARE instruction to lexicographically compare two pairs. However, due to a missing case in the type-checker for comparable types, the Babylon implementation of comparable pairs did not allow the use of pairs as elements in sets nor keys in maps and big maps. This is fixed in Carthage.

### Fixing MAPping on maps with side effects¶

The MAP instruction can be used in Michelson to apply a function to each element of a list or each value of a map, producing respectively a list of the same length as the original or a map with the same keys.

During the development of a new unit test suite for the Michelson language, the Runtime Verification team discovered that the Michelson interpreter incorrectly handled side effects in the map case of the MAP instruction. Until Babylon, if the body of the MAP instruction modifies the remaining of the stack, then these changes are reverted when the MAP exits. This behaviour is consistent with neither the Michelson documentation nor the list case; it has been fixed in Carthage.

This change is not backward compatible so we have inspected the current state of the mainnet chain and we have checked that, at time of writing, no contract is affected by this bug. Until the activation of Carthage (or any protocol including this fix), smart contract authors should avoid relying on the bogus behaviour of the MAP instruction on maps by using the ITER instruction instead when they need to perform side effects on the remaining of the stack during an iteration.

### Dead optimisation of the UNPAIR macro¶

The UNPAIR macro is very commonly used in Michelson to destruct pairs. In order to encourage its use, it received a special treatment in Babylon by which its gas cost was artificially decreased. Unfortunately, a small mistake in the unfolding of the UNPAIR macro made this special treatment dead code; the interpreter is looking for the sequence {DUP; CAR; DIP CDR} but the unfolding of UNPAIR is actually {DUP; CAR; DIP {CDR}} (note the extra pair of curly braces around CDR). Moreover, the Babylon gas update has made this peephole optimisation of the UNPAIR macro much less interesting because the gas costs of all stack and pair instructions are much lower than in previous protocols. We plan to promote UNPAIR as a new Michelson instruction in a future protocol proposal.

### Error message for EMPTY_BIG_MAP arity¶

The EMPTY_BIG_MAP instruction, which was added in Babylon and can be used to push an empty big_map on the stack, expects two parameters (the types for keys and values). When the instruction is used with another arity, the error message produced in Babylon was unclear because of a missing case in the type checker. This missing case has been added and the error message is clearer in Carthage.

### Typechecking big_map literals¶

The typechecking RPCs typecheck_script and typecheck_data are useful tools for Michelson editors featuring typechecking. The typecheck_data RPC was restricted to non-big_map types for no good reason. This limitation has been removed; it is possible in Carthage to typecheck big_map literals.

### Checking validity of annotations¶

Annotations are enforced to only contain valid JSON.

## Changes to RPCs¶

BREAKING CHANGES: the semantics of the baking_rights RPC and the return values of the block_reward and endorsement_reward RPCs have changed.

Below you can find all the RPC changes.

### Baking_rights¶

In Babylon the argument max_priority causes the RPC to return the rights up to max_priority excluded, for example setting max_priority=0 returns the empty list. In Carthage the value of max_priority is included, for example max_priority=0 returns the rights of priority zero.

### Block_reward¶

This constant is accessed by calling /chains/main/blocks/head/constants, which returns a JSON object where the field block_reward was renamed to baking_reward_per_endorsement and its value was changed from a single value to a list of values.

### Endorsement_reward¶

This constant is accessed by calling /chains/main/blocks/head/constants, which returns a JSON object where the value of the field endorsement_reward was changed from a single value to a list of values.

## Changes to the binary format of operations¶

There are no changes to the binary format of operations.

## Changelog¶

You can see the full git history on the branch proto-006. In order to regenerate a protocol with the same hash as Carthage you can run from this branch:

$./scripts/snapshot_alpha.sh carthage_006 from babylon_005$ ls src/proto_006_PtXXX


### Detailed Changelog¶

• Proto: remove .ocamlformat-ignore and make fmt

Apply the ocamlformat tool to the protocol codebase.

• Protocol/Migration: remove babylon’s vanity nonce

• Protocol/Storage: initialize big_map ids only for genesis

• Protocol/RPC: fix ‘baking_rights’ so that ‘max_priority’ is included

Fix a bug where the ../helpers/baking_rights RPC would exclude the
max_priority baking right from its result.

BREAKING CHANGE: the semantics of the baking_rights RPC has changed

• Protocol/Emmy+: fix baking and endorsement reward formulae

Fix the imprecision in the baking reward formula to make it linear in
the number of endorsements included instead of a step function.

Improve the precision on the endorsement reward computation by
applying the priority malus on the total endorsement reward.

• Protocol/Michelson: fix comparable comb pairs

Allow comb pairs as map keys and set elements, not only as operands of
COMPARE.

• Protocol/Michelson: allow all parameter types when typechecking a literal

Extend the range of the typecheck_data RPC by also allowing big_map
values.

• Protocol/Gas: increase the gas limits per block and operation by 30%

Bump the gas limit for blocks and operations by 30% going from 800000
per operation and 8000000 per block to 104000 per operation and
1040000 per block.

• Protocol/Migration: bump gas limit constants in the context

Update the gas limit constants in the context on protocol transition.

• Protocol/Michelson: remove the peephole optimisation of UNPAIR

Remove an unreachable optimisation. A proper UNPAIR instruction shall

• Protocol/Michelson: handling of the bad arity error for the EMPTY_BIG_MAP instruction

Improve error reporting when checking for the arity of the
EMPTY_BIG_MAP instruction

• Protocol/Michelson: fix the interpretation of the MAP instruction on maps

In the previous implementation, accumulating a value during a MAP on a
map was impossible because the initial stack tail was restored. This
was not the documented behavior of the MAP instruction and it was
inconsistent with the case of mapping over a list.

BREAKING CHANGE: originated contracts that rely on the previous (and
incorrect) semantics might behave incorrectly.

• Protocol/Michelson: improve the performance of the CONTRACT instruction

Add an optimisation that make the instruction cheaper in gas for
implicit contracts (tz1, tz2, tz3) by saving an I/O.