How to infer rounding and/or saturation into a DSP block

Hi,

I'm inferring most of my filters/equations in DSP blocks from HDL code, which works good. I would like to know if it is possible to infer rounding and/or saturation in the First/Second Round/Saturate stage of the Stratix III DSP block. I did not found any recommended HDL coding style for this part. Does anyone here know how I could do it?

Tool: Quartus II 9.1 SP1

Device: Stratix III (but I think all DSP blocks of the Stratix family are the same?)