How to choose device : CPLD or FPGA ?

In that case, you'll probably need multipliers. They can be done without dedicated multipliers but you need as many adders per multiplier as you have bits.

If that is all it is you might be able to squeeze it into a large CPLD, but it might be easiest to go with an FPGA. Also, try not to do division on either CPLD or FPGA, its much easier to multiply by 1/n rather than divide by n.

Thirdly, if you're thinking about floating point, try changing everything to fixed point. FPGAs dont like floating point and you would really struggle on CPLDs.

Thanks Tricky.

My polynomial equation is of 3rd order and I need to process only one input signal.

CPLDs are very small devices with no dedicated internal rams or multipliers. FPGAs have internal rams and multipliers. CPLDs are very cheap, FPGAs range from cheap to very expensive.

So if you know its a very simple design with no need for any serious maths or storage, stick with a CPLD. Otherwise you will need an FPGA.

As for estimating your LEs, best way is to write the source code and compile it. estimating LEs for designs more complicated than a few gates is dufficult. On the other hand it can be easy to estimate memory and multiplier requirements.