A method for calculating FP (Full Precision) and PP (Partial Precision) values, performed by an ID (Instruction Decode) unit, contains at least the following steps: decoding an instruction request from a compiler; executing a loop m times to generate m microinstructions for calculating first-type data, or n times to generate n microinstructions for calculating second-type data according to the instruction mode of the instruction request, thereby enabling ALGs (Arithmetic Logic Groups) to execute lanes of a thread. m is less than n and the precision of the first-type data is lower than the precision of the second-type data.