Apple II 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