1. A configurable execution unit comprising operators capable of being dynamically configured at the level of processing multi-bit operand values by an instruction, comprising: one or more dynamically configurable operator modules, the or each module being connectable to receive input operands indicated in an instruction; and a programmable lookup table connectable to receive dynamic configuration information determined from an opcode portion of an instruction and capable of generating operator configuration settings defining an aspect of the function and/or behaviour of said configurable operator module, responsive to said dynamic configuration information in the instruction.