High-sticky calculation in pipelined fused multiply/add circuitry

摘要

Arithmetic processing circuits in a circuit in a floating point processor having a fused multiply/ADD circuitry. In order to avoid waiting cycles in the normalizer of the floating point arithmetic, control logic calculates in an extremely early state of the overall Multiply/Add processing. Parts of the intermediate add result are significant and have to be selected in the pre-normalizer multiplexer to be fed to the normalizer by counting the leading zero bits (LAB) of the addend in a dedicated circuit right at the beginning of the pipe. LAB is added to the shift amount (SA) that is calculated to align the addend and is then compared with the width of the incrementer. If the sum of (SA+LAB) is larger than the width of the incrementer, which is a constant value, then no significant bits are in the high-part of the intermediate result, and the pre-normalizer multiplexer selects the data from a second predetermined position, otherwise from a first predetermined position.