Methods and apparatus for fast fourier transforms

(54) METHODS AND APPARATUS FOR FAST FOURIER TRANSFORMS

(75) Inventor: Jonathan E. Greene, Great Barrington, MA (US)

(73) Assignee: Mercury Computer Systems, Inc.,

Chelmsford, MA (US)

( * ) Notice: Subject to any disclaimer, the term of this patent is extended or adjusted under 35 U.S.C. 154(b) by 253 days.

(21) Appl. No.: 09/728,469

(22) Filed: Nov. 30, 2000

Related U.S. Application Data

(60) Provisional application No. 60/192,639, filed on Mar. 27, 2000, and provisional application No. 60/168,027, filed on Nov. 30, 1999.

(51) Int. CI.7 G06F 15/00

(52) U.S. CI 708/404

(58) Field of Search 708/400, 403,

708/404, 405, 406, 408, 409

708/404

A system for calculating fast Fourier transforms includes a non-final stage calculating means for repetitively performing in-place butterfly calculations for n-1 stages as well as a final stage calculating means for performing a final stage of butterfly calculations. The final stage calculating means includes a first loop and a second loop. The first loop performs a portion of the final stage butterfly calculations by iterating on a table of first loop index values consisting of values that bit-reverse into themselves. The first loop also includes control logic to select inputs for groups of butterfly calculations based on the first loop index values. The second loop performs a remaining portion of the final stage butterfly calculations by iterating on a table of second loop index value pairs consisting of two values that bit-reverse into each other. The second loop includes control logic to select inputs for two groups of butterfly calculations based on the two second loop index pair values respectively.

46 Claims, 4 Drawing Sheets