pwasm-ewasm-diff.md

EWasm eth interface https://github.com/ewasm/design/blob/master/eth_interface.md

Glosarry:

• pwasm - Parity Wasm
• ewasm - Ethereum Wasm

Notable differences:

Calling into contract

In pwasm, runtime prepares the environment, i.e. allocates memory for and copies input data into this memory, and then calls into _call(*const Descriptor) function. To return the execution result, contract needs to write result's data into a location in the memory designated by the Descriptor.

Descriptor definition looks like this:

struct Descriptor {
  args_ptr: *const u8,
  args_len: usize,
  result_ptr: *const u8,
  result_len: usize,
}

Runtime environment

pwasm publishes some functions that can be commonly found in the libc, namely:

• malloc,
• free,
• memcpy,
• memmemove,
• memset,

Extracting this functions might improve binary size and performance of a contract.

Also, pwasm provides several functions:

• debug, log message into the console,
• panic, traps immediatelly with provided message/payload,

Misc

• pwasm's uses U256 to represent value, whereas ewasm uses u128,
• pwasm's gas expects i32 arguments, whereas ewasm's useGas uses i64,
• pwasm's blockhash might return error (according to signature), ewasm's not.
• at the moment, there is no way to limit amount of gas transfered into a call in pwasm, but it is planned to fix this,
• pwasm's call returns -1 to denote error state,
• pwasm's log accepts topic_count and pointer to array of the topic values, whereas ewasm's log takes pointers to each topic's value separately.
• pwasm's gaslimit returns U256, whereas ewasm uses i64,

few notes

there is no way to limit amount of gas transfered into a call in pwasm

it's not intentionally, will be fixed

pwasm's balance returns H256, wheres ewasm's getBalance returns u128,

U256 to be exact

Fixed, thanks @fckt!