M-1093 Nov60

This preliminary interoffice memorandum (M-1093), dated November 22, 1960, describes the ARCSINE and ARCCOSINE subroutines developed by Chas. W. Adams Associates, Inc. for the PDP-1 computer, and distributed to the PDP Distribution List.

The document details the input and output specifications for these subroutines:

• Input Argument: The argument's binary point is considered to be immediately to the right of the sign position, ranging from approximately -1.0 to +1.0.
• Output Result: The answer is given in radians, scaled by a factor of 2^-3 (binary point three positions to the right of the sign position), to maintain compatibility with existing sine and cosine subroutines.
• Result Ranges: The arccosine routine yields results from 0 to pi radians, while the arcsine routine yields results from -pi/2 to +pi/2 radians.

The subroutines rely on other dependent routines, including a "modified multiply," square root, and divide subroutines. The memo also outlines the calling sequence (using LIO and JSP instructions) and provides a symbolic assembly language listing for the ARCSIN and ARCCOS subroutines, including calls to necessary sub-routines (like SQROOT and MULTIP) and defined constants.