code: func (c *sha256hash) RequiredGas(input []byte) uint64 {
  	return uint64(len(input)+31)/32*params.Sha256PerWordGas + params.Sha256BaseGas
  }
docs: // RequiredGas returns the gas required to execute the pre-compiled contract.
  //
  // This method does not require any overflow checking as the input size gas costs
  // required for anything significant is so high it's impossible to pay for.