Apple II User Manual

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|  TOPIC -- Apple II -- IA Floating point article

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Interface Age, November 1976, pages 103-111.

Floating Point Routines for the 6502*

    by Roy Rankin

Department of Mechanical Engineering, Stanford University

    and Steve Wozniak

Apple Computer Company

*First appeared in Dr. DOBB's Journal of Computer Calisthenics &

Orthodontia, Box 310, Menlo Park, CA 94025

The following floating point routines represent a joint

effort between Steve Wozniak who wrote the basic float-

ing point routines of FADD, FSUB, FMUL, FDIV and

their support routines and myself, Roy Rankin, who

added FIX, FLOAT, LOG, LOG10, and EXP.  The basic

floating point routines are failry Machine dependent, but

the transcendental programs should be very easy to

transport from one machine to another.  The routines

consist of the following math functions

     * LOG         Natural log

     * LOG10       Base 10 log

     * EXP         Exponential

     * FADD        Floating add

     * FSUB        Floating subtraction

     * FMUL        Floating multiplication

     * FDIV        Floating division

     * FIX         Convert floating to fixed

     * FLOAT       Convert fixed to floating

Two additional routines exchange the contents of

exp/mant1 with exp/mant2 and compliments exp/

mant1.  These routines are

SWAP          Exchange the contents of exp/mant 1 with

              exp/mant 2

FCOMPL        Compliment exp/mant 1

Floating point numbers are represented by 4 bytes as

shown in the following

 +- SIGN BIT     +- SIGN BIT

 |  0 = +        |  0 = +

 |  1 = -        |  1 = -

 v               v

|S|             |S| +- PRESUMED DECIMAL POINT

|B|             |B| v

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