Identity function

This precompiled contract performs the identity function. In mathematics, an identity function is a function that always returns the same value as its argument. In this context, the contract takes the input data and returns it as is. This precompiled contract resides at the hardcoded Ethereum address 0x0000000000000000000000000000000000000004.

The identity_run function takes two arguments: input data, which it returns unaltered, and gas_limit which defines the maximum computational work the function is allowed to do. A linear gas cost calculation based on the size of the input data and two constants, IDENTITY_BASE (the base cost of the operation) and IDENTITY_PER_WORD (the cost per word), is performed. If the calculated gas cost exceeds the gas_limit, an Error::OutOfGas is returned.

This identity function can be useful in various scenarios such as forwarding data or acting as a data validation check within a contract. Despite its simplicity, it contributes to the flexibility and broad utility of the Ethereum platform.