M-1096 Jan61

This interoffice memorandum from January 19, 1961, issued by DEC's Computer Division to the PDP Distribution List, details a "Multiply Subroutine" (M-1096).

The document provides the assembly language listing for this library subroutine, which was developed for the PDP-1 computer by Bolt, Beranek and Newman. The subroutine offers two entry points for multiplication, each designed for different precision requirements:

1. mpy: Performs a full-precision multiplication. When called, it returns the answer as a sign and 34 bits (representing the product), along with an additional sign, stored across the Accumulator (AC) and Input/Output (IO) registers.
2. i-mpy: Performs an integer multiplication. When called, it returns a sign and the low 17 bits of the product in the AC register.

The memo explains the input format (two factors) and the output register usage for each multiplication mode.