@polygon-hermez/vm/src/evm/precompiles/04-identity.ts

An Ethereum VM implementation

import { BN } from 'ethereumjs-util'
import { PrecompileInput } from './types'
import { OOGResult, ExecResult } from '../evm'
const assert = require('assert')

export default function (opts: PrecompileInput): ExecResult {
  assert(opts.data)

  const data = opts.data
  const gasUsed = new BN(opts._common.param('gasPrices', 'identity'))
  gasUsed.iadd(
    new BN(opts._common.param('gasPrices', 'identityWord')).imuln(Math.ceil(data.length / 32))
  )

  if (opts.gasLimit.lt(gasUsed)) {
    return OOGResult(opts.gasLimit)
  }

  // Reduce counters
  opts._VM.vcm.computeFunctionCounters('preIdentity', {
    calldataLength: data.length,
    returnDataLength: opts.outLength.toNumber(),
  })

  return {
    gasUsed,
    returnValue: data,
  }
}