A programmable digital signal processor with 32b floating point arithmetic

Leading zero anticipation and detection-a comparison of methods

“…(2) and (3) can be simplified further when the detection is restricted to only leading zeros or leading ones. For example, when the circuit for detection of leading zeros does not need to consider cases where leading ones might result, then the leading zero indicator can be simplified to Further simplification results for a case which is even more restricted, as described in [8J and [SI.…”

“…(1) is referred to as Kershaw, (the earliest reference), the LZA described by equ. (2) and (3) is referred to as Schmookler, and the LZA described by equ. (4) and (5) is referred to as Britton. Only Kershaw and Schmookler cover both leading zeros and ones, without using any carry signals from the adder.…”

“…The creation of the monotonic string can be accomplished through the use of Manchester carry techniques [2] [31 or through hierarchical or look-ahead techniques [41.…”

“…In Kersaw [2][3], generating the count from a monotonic string is dictated by the use of precharged chains. One small circuit integrates the adder and LZA functions together.…”

“…The earliest description of an LZA known to the authors is by Kershaw, et a1 [2][3] which shows a Manchester carry adder circuit with a second precharged circuit used for the detection of the leftmost significant digit. It works for both leading zeros when the rcsult of a subtraction is positive, and for leading ones when the result is negative.…”