Reducing the cost of floating-point mantissa alignment and normalization in FPGAs

In floating-point datapaths synthesized on FPGAs, the shifters that perform mantissa alignment and normalization consume a disproportionate number of LUTs. Shifters are implemented using several rows of small multiplexers; unfortunately, multiplexerbased logic structures map poorly onto LUTs. FPGAs, meanwhile, contain a large number of multiplexers in the programmable routing network; these multiplexer are placed under static control of the FPGA’s configuration bitstream. In this work, we modify some of the routing multiplexers in the intracluster routing network of a CLB in an FPGA to implement shifters for floating-point mantissa alignment and normalization; the number of CLBs required for these operations is reduced by 67%. If shifting is not required, the routing multiplexers that have been modified can be configured to operate as normal routing multiplexers, so no functionality is sacrificed. The area overhead incurred by these modifications is small, and there is no need to mo...

• Type: Journal
• Year: 2012
• Where: FPGA
• Authors: Yehdhih Ould Mohammed Moctar, Nithin George, Hadi Parandeh-Afshar, Paolo Ienne, Guy G. F. Lemieux, Philip Brisk
• Keywords: Field Programmable Gate Array, FPGA, FPGA 2012, Logic Structures, Programmable Gate Array