Apple II User Manual

FSUB subroutine (address $F468)

Purpose: To subtract two floating point numbers.

Entry: The minuend is in FP1 and the subtrahend is in FP2.  Both should be

normalized to retain maximum precision prior to calling FSUB.

Uses: FCOMPL, ALGNSWP, FADD, ADD, NORM, RTLOG.

Exit: The normalized difference is in FP1 with the mantissa truncated to 24

bits.  FP2 holds either the minued or the negated subtrahend, whichever is

of greater magnitude.  E is altered but SIGN and SCR are not.  the A-REG is

altered and the X-REG is cleared.  The Y-REG is not disturbed.

Cautions: An exit to location S3F5 is taken if the result is less than

-2^128 or greater than +2^128-1.  or if the subtrahend is -2^128.

Example: Prior to calling FSUB, FP1 contains +7 (minuend) and FP2 contalns

-5 (subtrahend).

      _____    _____    _____    _____

     |     |  |     |  |     |  |     |

FP1: | $82 |  | $70 |  |  0  |  |  0  |   (+12)

     |_____|  |_____|  |_____|  |_____|

       X1       M1

      _____    _____    _____    _____

     |     |  |     |  |     |  |     |

FP2: | $82 |  | $B0 |  |  0  |  |  0  |   (- 5)

     |_____|  |_____|  |_____|  |_____|

       X2       M2

After calling FSUB, FP1 contains +12 and FP2 contains +7.

      _____    _____    _____    _____

     |     |  |     |  |     |  |     |

FP1: | $83 |  | $60 |  |  0  |  |  0  |   (+12)

     |_____|  |_____|  |_____|  |_____|

       X1       M1

FMUL subroutine (address $F48C)

Purpose: To multiply floating point numbers.

Entry: The multiplicand and multiplier must reside in FP1 and FP2

respectively.  Both should be normalized prior to calling FMUL to retain

maximum precision.

Uses: MD1, MD2, RTLOG1, ADD, MDEND.

Exit: The signed normalized floating point product is left in FP1.  M1 is