The present invention provides permutation instructions which can be used in software executed in a programmable processor for solving permutation problems in both cryptography and multimedia. For fast cryptography, bit-level permutations are used, whereas for multimedia, permutations on subwords of typically 8 bits or 16 bits are used. Permutation instructions of the present invention can be used to provide any arbitrary permutation of sixty-four 1-bit subwords in a 64-bit processor, i.e., a processor with 64-bit words, registers and datapaths, for use in fast cryptography. The permutation instructions of the present invention can also be used for permuting subwords greater than 1 bit in size, for use in fast multimedia processing. For example, in addition to being able to permute sixty-four 1-bit subwords in a register, the permutation instructions and underlying functional unit can permute thirty-two 2-bit subwords, sixteen 4-bit subwords, eight 8-bit subwords, four 16-bit subwords, or two 32-bit subwords. The permutation instructions of the present invention can be added as new instructions to the Instruction Set Architecture of a conventional microprocessor, or they can be used in the design of new processors or coprocessors to be efficient for both cryptography and multimedia software.

The method for performing permutations is by constructing a Benes interconnection network. This is done by executing a certain number of stages of the Benes network with permute instructions. The permute instructions are performed by a circuit comprising Benes network stages. Intermediate sequences of bits are defined that an initial sequence of bits from a source register are transformed into. Each intermediate sequence of bits is used as input to a subsequent permutation instruction. Permutation instructions are determined for permuting the initial source sequence of bits into one or more intermediate sequence of bits until a desired sequence is obtained. The intermediate sequences of bits are determined by configuration bits. The permutation instructions form a permutation instruction sequence. At most lg n permutation instructions are used in the permutation instruction sequence.

In an embodiment of the present invention, multibit subwords are permuted by eliminating pass-throughs in the Benes network. In a further embodiment of the invention, the method and system are scaled for performing permutations of 2n bits in which subwords are packed into two or more registers. In this embodiment, at most 4 lg n + 2 instructions are used to permute 2n bits using n-bit words.