FADD subroutine (address $F46E)

Purpose: To add two numbers in floating point form.

Entry: The two addends are in FP1 and FP2 respectively. For maximum precision, both should be normalized.

Uses: SWPALGN, ADD, NORM, RTLOG.

Exit: The normalized sum is left in FP1. FP2 contains the addend of greatest magnitude. E is altered but sign is not. The A-REG is altered and the X-REG is cleared. The sum mantissa is truncated to 24 bits.

Caution: Overflow may result if the sum is less that -2^128 or greater than +2^128-1. If so, a jump to location $3F5 is executed leaving 0 in X1, and twice the proper sum in the mantissa M1. The sign bit is left in the carry, 0 for positive, 1 for negative.

 

_____

 

 

__________

 

FP1:

0

X.YYY...

_____

__________

 

X1

 

 

M1

(For carry=0, true sum=+X.YYY x 2^128)

Example: Prior to calling FADD, FP1 contains +12 and FP2 contains -5.

 

_____

 

_____

 

_____

 

 

_____

 

 

 

 

 

 

 

FP1:

$83

$60

0

0

(+12)

_____

_____

_____

_____

 

 

X1

 

 

M1

 

 

 

 

 

 

 

 

 

_____

 

_____

 

_____

 

 

_____

 

 

 

 

 

 

 

FP2:

$82

$B0

0

0

(-5)

_____

_____

_____

_____

 

X2 M2

After calling FADD, FP1 contains +7 (FP2 contains +12).

 

_____

 

_____

 

_____

 

_____

 

 

FP1

$82

$70

0

0

(+7)

_____

_____

_____

_____

 

 

X1

 

M1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 71
Image 71
Apple II manual

II specifications

The Apple II, launched in April 1977, was one of the first highly successful mass-produced microcomputer products. It marked a significant leap in personal computing, setting standards for future developments in the industry. Created by Steve Wozniak and Steve Jobs, the Apple II differentiated itself with its user-friendly design, appealing aesthetics, and robust capabilities.

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