M-1097 Jan61

This interoffice memorandum (M-1097), dated January 19, 1961, from Digital Equipment Corporation's Computer Division, describes a "Divide Subroutine" for the PDP-1 computer.

The routine, developed by Bolt, Beranek and Newman, provides two main functionalities:

1. Fractional Divide:

   • Handles signed 34-bit dividends, where the high-order part is in the Accumulator (AC) and the low-order part (up to bit 17) is in the In-Out (IO) register.
   • Checks for error conditions such as a zero divisor or a divisor less than or equal to the high-order part of the dividend.

2. Integer Divide:

   • Handles signed 17-bit dividends, which are loaded into the IO register.
   • Checks for a zero divisor.
   • Upon successful completion, the quotient is returned in the AC and the remainder in the IO register.

The document includes the complete assembly language listing for both the fractional and integer divide routines.