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Article #40 (145 is last):
Newsgroups: freenet.sci.comp.atari.library
From: aa384 (Doug Wokoun)
Subject: ATR: chpt.11: Floating Point Package
Date: Mon Dec 25 06:07:41 1989


                                  CHAPTER 11
     
     
                     THE FLOATING POINT ARITHMETIC PACKAGE
     
     
     The routines which do floating point arithmetic are a part of the
     operating system ROM.  The Atari computer uses the 6502's decimal math
     mode.  This mode uses numbers represented in packed Binary Coded
     Decimal (BCD).  This means that each byte of a floating point number
     holds two decimal digits.  The actual method of representing a full
     number is complicated and probably not very important to a programmer.
     However, for those with the knowledge to use it, the format is given
     below.
     
                     Floating point number representation
     
     
               byte 0    xx   excess 64 exponent + sign
                         xx \
                         xx  \
                         xx   > 10 BCD digits
                         xx  /
               byte 7    xx /
     
     
     The decimal point is shifted to left of the MSD and the exponent is
     adjusted accordingly.  Therefore, the decimal point doesn't need to be
     represented.
     
     For programming purposes, floating point numbers can be in ASCII code.
     It takes up to 14 bytes to store a floating point number in this
     manner.  The floating point package has a routine to convert numbers
     between ASCII and floating point.
     
     USE OF THE FLOATING POINT PACKAGE
     
     The floating point package has several routines to convert between
     ASCII and FP and to do the arithmetic functions.  These are the
     important data base variables.
     
                      Floating point data base variables
     
     
     FR0    $00D4,6    (212): 6 byte buffer for floating point number
     FR1    $00E0,6    (224): 6 byte buffer for floating point number
     CIX    $00F2      (242): index for INBUFF address
     INBUFF $00F3,2    (243): 2 byte pointer to ASCII floating point number
     FLPTR  $00FC,2    (252): 2 byte pointer to user buffer for floating
                               point number
     LBUFF  $0580,?   (1408): result buffer for FASC routine
     
     MAKING THE CALL
     
     To do a floating point function, first set the proper pointers and JSR
     to the operation entry point.  Below is a list of the entry points and
     parameters.
     
     ASCII to floating point
     
     Converts ASCII representation pointed to by INBUFF to FP in FR0.
     
      AFP    = $D800
     
      INBUFF = address of ASCII number
     
      CIX    = buffer offset if any
     
      JSR AFP
     
     
     FLOATING POINT TO ASCII
     
     Converts floating Point number  in FR0 to ASCII.  The result will be
     in LBUFF.  INBUFF will point to the ASCII number which will have the
     bit 7 of the last byte set to 1.
     
      FASC   = $D8E6
     
      JSR FASC
     
     INTEGER TO FLOATING POINT CONVERSION.
     
     Converts a 2 byte unsigned integer (0 to 65535) in FR0 to floating
     point in FR0.
     
      IFP    = $D9AA
     
      JSR IFP
     
     FLOATING POINT TO INTEGER CONVERSION.
     
     Converts floating point number in FR0 to 2 byte integer in FR0.
     
      FPI     = $D9D2
     
      JSR FPI
      BCS overflow
     
     ADDITION
     
     Adds floating point numbers in FR0 and FR1 with result in FR0.

      FADD    = $DA66
     
      JSR FADD
      BCS out of range
     
     
     SUBTRACTION
     
     subtracts FR1 from FR0 with the result in FR0.
     
      FSUB    = $DA60
     
      JSR FSUB
      BCS out of range
     
     MULTIPLICATION
     
     Multiplies FR0 by FR1 with the result in FR0.
     
      FMUL    = $DADB
     
      JSR FMUL
      BCS out of range
     
     DIVISION
     
     Divides FR0 by FR1 with result in FR0.
     
      FDIV    = $DB28
     
      JSR FDIV
      BCS out of range or divisor is 0
     
     LOGARITHMS
     
     Puts logarithm of FR0 in FR0
     
      LOG     = $DECD
      LOG10   = $DED1
     
      JSR LOG ;for natural log.
     
     or
     
      JSR LOG10 ;for base 10 log.
      BCS negative number or overflow
     
     
     EXPONENTIATION
     
     Put exponentiation of FR0 in FR0
     
      EXP     = $DDC0

      EXP10   = $DDCC
     
      JSR EXP ;for e ** Z
     
     or
     
      JSR EXP10 ;for 10 ** Z
     
     
     POLYNOMIAL EVALUATION
     
     Puts the result of an n degree polynomial evaluation  of FR0 in FR0.
     
      PLYEVL  = $DD40
     
      LDX LSB of pointer to list of floating point
          coefficients, ordered high to low.
      LDY MSB of above
      LDA number of coefficients in list
     
      JSR PLYEVL
      BCS overflow
     
     CLEAR FR0
     
     Sets FR0 to all zeroes
     
      ZFR0    = $DA44
     
      JSR ZFR0
     
     CLEAR ZERO PAGE FLOATING POINT NUMBER
     
     Clears user floating point number in page zero.
     
      ZF1     = $DA46
     
      LDX address of zero page FP buffer
     
      JSR ZF1
     
     LOAD FR0 WITH FLOATING POINT NUMBER
     
     Loads FR0 with user FP number in buffer pointed to by 6502 X and Y
     registers or by FLPTR.  After either operation below, FLPTR will point
     to the user FP buffer.
     
      FLD0R   = $DD89
     
      LDX lsb of pointer
      LDY msb
     
      JSR FLD0R
    
     or
     
      FLD0P   = $DD8D
     
      FLPTR   = address of FP number
     
      JSR FLD0P
     
     LOAD FR1 WITH FLOATING POINT NUMBER
     
     Loads FR1 with user FP number in buffer pointed to by 6502 X and Y
     registers or by FLPTR.  After either operation below, FLPTR will point
     to the user FP buffer.
     
      FLD1R   = $DD98
     
      LDX lsb of pointer
      LDY msb
     
      JSR FLD1R
     
     or
     
      FLD1P   = $DD9C
     
      FLPTR   = address of FP number
     
      JSR FLD1P
     
     STORE FR0 IN USER BUFFER
     
     stores the contents of FR0 in user FP buffer pointed to by 6502 X and
     Y registers or by FLPTR.  After either operation below, FLPTR will
     point to the user FP buffer.
     
     
      FST0R   = $DDA7
     
      LDX lsb of pointer
      LDY msb
     
      JSR FST0R
     
     or
     
      FST0P   = $DDAB
     
      FLPTR   = address of FP number
     
      JSR FST0P
     
     MOVE FR0 TO FR1

     
     Moves the contents of FR0 to FR1
     
     
      FMOVE   = $DDB6
     
      JSR FMOVE
     
     
     The usual use sequence of the floating point package might be to:
     
     load FR0 and FR1 with FP numbes from user specified buffers
     
     do the math
     
     then store FR0 in a user buffer.
     
     An alternative might be to:
     
     convert an ASCII representation to FP (the result is automatically in
     FR0).
     
     move FR0 to FR1.
     
     Convert the second ASCII number.
     
     Do the math.
     
     Convert FR0 back to ASCII.
     
     Store the number back into a user buffer.
     
     
     The floating point package uses the following blocks of RAM.
     
     
                      RAM used by floating point package
     
     
          $00D4 - $00FF
          $057E - $05FF
     
     
     If the floating point package is not used the above ram is free.
     
     
     
                   Useful data base variables and OS equates
     
     
     FR0    $00D4,6      (212): system FP buffer
     FR1    $00E0,6      (224): system FP buffer
     CIX    $00F2        (242): INBUFF index
     INBUFF $00F3,2      (243): pointer to ASCII FP buffer
     FLPTR  $00FC,2      (252): pointer to user FP buffer
     LBUFF  $0580       (1408): result buffer for FP to ASCII
     AFP    $D800      (55296): ASCII to FP
     FASC   $D8E6      (55526): FP to ASCII
     IFP    $D9AA      (55722): integer to FP
     FPI    $D9D2      (55762): FP to integer
     ZFR0   $DA44      (55876): clear FR0
     ZF1    $DA46      (55878): clear zero page FP buffer
     FSUB   $DA60      (55904): FR0 - FR1
     FADD   $DA66      (55910): FR0 + FR1
     FMUL   $DADB      (56027): FR0 * FR1
     FDIV   $DB28      (56104): FR0 / FR1
     FLD0R  $DD89      (56713): load FR0 by X,Y pointer
     FLD0P  $DD8D      (56717): load FR0 by FLPTR pointer
     FLD1R  $DD98      (56728): load FR1 by X,Y pointer
     FLD1P  $DD9C      (56732): load FR1 by FLPTR pointer
     FST0R  $DDA7      (56743): store FR0 at buffer by X,Y pointer
     FST1P  $DDAB      (56747): store FR0 at buffer by FLPTR pointer
     FMOVE  $DDB6      (56758): move FR0 to FR1
     EXP    $DDC0      (56768): e exponentiation
     EXP10  $DDCC      (56780): base 10 exponentiation
     PLYEVL $DD40      (56640): polynomial evaluation
     LOG    $DECD      (57037): natural log of FR0
     LOG10  $DED1      (57041): base 10 log of FR0
                                                                           
-- 
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