Low Density Parity Checks (IDPC) are a method of error detection and correction that are able to achieve near Shannon-limit channel communication. LDPC decoders involve a series of computations between two units, the check node and the bit node. In this paper we propose the use of an approximation unit to perform the check node operation. Additionally, we propose a ROM based look-up table (LUT) as a function approximation technique, to be used with an LDPC decoder. The paper shows that a ROM based LUT achieves better performance than using a piecewise linear approximation method to approximate the LDPC computation function. Furthermore, this paper shows that the ROM LUT method can gradually take over as the selected function approximation technique for computationally intensive demanding VLSI designs as the technology shifts to the nanometer era.