FUNCTION CALLING MECHANISM WITH EMBEDDED INDEX FOR A HANDLER PROGRAM AND AN EMBEDDED IMMEDIATE VALUE FOR PASSING A PARAMETER

A data processing system 2 is provided which includes an instruction decoder 18 responsive to a handler branch instruction HLB, HBLP which includes an index value field to calculate a handler pointer in dependence upon a handler base address HBA and the index value field and then to branch to that handler pointer position. A handler program 24, 26 at the branch target is then executed following which a return is made to an address following the handler branch instruction using a link address value stored when the handler branch instruction was executed.