EVM Precompiled Contracts

Precompiles in Solidity is a native way to speed up general but expensive functions and interacts with something outside the VM. For example, ECRecover precompiled smart contracts definitely boost public key recovery functions because of execution almost on the hardware level. From another side, the Plasm Network includes dispatch precompiled smart contracts, that permit Solidity developers to interact with other Plasm runtime modules.
The ECRecover precompile
The ECRecover is a standard Solidity precompiled smart contract available at the address 0x01. It is used in most contracts to improve ECDSA performance during recovering signature signer account.
The Dispatch precompile
On standard Plasm Parachain runtime Dispatch smart-contract available at the address:
0x0000000000000000000000000000000000000006
Internally, this contract just decodes input data as Call structure
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let call = T::Call::decode(&mut &input[..]).map_err(|_| ExitError::Other("decode failed".into()))?;
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and then executes it as a transaction from smart contract origin.
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let origin = T::AddressMapping::into_account_id(context.caller);
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match call.dispatch(Some(origin).into()) {
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...
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That  means each EVM smart contract could call any available method of runtime using Solidity standard call() function to the precompiled contract address.
Solidity SCALE codec
The difficulty for Solidity developers is that the SCALE codec isn't available for Solidity. As a  result, they should encode call parameters manually that could be complex and expensive.
But for calling standard or trivial methods it's not a big problem. For example, call Balances::transfer() for 5FHneW46xGXgs5mUiveU4sbTyGBzmstUspZC92UhjJM694ty and 42 looks like:
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0x0400008eaf04151687736326c9fea17e25fc5287613693c912909cb226aa4794f26a48a8
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Where 0x04 is a module index, following 0x00 is a method index in the module and next is address and balance parameters. If your contract should constantly transfer the same amount to the same destination, then a constant call string could be used.

Ethereum Contract on Dusty Network

FAQ for EVM smart contract deployment

Last modified 7mo ago

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Contents

The ECRecover precompile

The Dispatch precompile

Solidity SCALE codec