Method and apparatus for generating an alignment control vector

Abstract

The data processing system loads three input operands, including two input vectors and a control vector, into vector registers and performs a permutation of the two input vectors as specified by the control vector, and further stores the result of the operation as the output operand in an output register. The control vector consists of sixteen indices, each uniquely identifying a single byte of input data in either of the input registers, and can be specified in the operational code or be the result of a computation previously performed within the vector registers. The control vector is specified by calculating the offset of a selected vector element of the input vector relative to a base address of the input vector and loading each element with an index equal to the relative offset. Alternatively, the generation of the alignment vector is made by performing a look-up within a look-up table. For additional loads from the same vector, the control vector does not change, since the alignment shift amount of the vector from an address boundary does not change. A permutation instruction can then be executed to load and shift the data to realign it in the output register at the vector boundary.