Extension of PDP-11 Instruction Set: Floating Point

This interoffice memorandum from December 22, 1969, by Grant Saviers to Bruce Delagi, discusses a proposed method for extending the PDP-11 instruction set to support floating-point operations (Add, Subtract, Multiply, Divide, Float, and Entier). The proposal involves interfacing a floating-point processor to the Unibus and associating six memory (I/O) locations with these functions. By utilizing the 'Move' instruction to pass an address pointer to a three-word table of operand addresses, the processor can execute operations more efficiently, requiring less core than standard memory-to-memory moves. The document includes a hand-translated code example of an arithmetic expression and considers the implications for subexpression optimization and future micro-programmed arithmetic processors.