Basic code

[Manuel Canales]

Can anybody help me write code to add, substract, multiply and divide using add and substract statements only ??

Thanks

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[Fred Oxenby]

you only need shift,add and XOR to perform add/subtract/multip./divide


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Fred
mailto:[email protected][email protected]</A>
http://www.oxenby.se

[Tom Hanlin]

Hmmm... is this a school assignment? Perhaps you should do it on your own?

I think it should be simple enough to add by adding, and subtract by subtracting,
unless your question left out something important?

Multiplication by addition, well. x * y is the same as x added to itself y times,
is it not? Likewise, x / y is about the same as subtracting y from x until y is
less than x...

I think there are BCD examples of handling this sort of issue in the PBWiz library
from Information Management Systems, if you need working code. See www.infoms.com
for details.

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Tom Hanlin
PowerBASIC Staff

[Buck Buchanan]

Manuel,

I'll leave the writing of the code to you, but here is an example
of adding to achieve multiplying. Let's multiple 126 times 624.

126
x 624
-----

First add 126 4 times.
Now add 1260 2 times.
and now add 12600 6 times.

The addition problem would look something like this:

126
126
126
126
1260
1260
12600
12600
12600
12600
12600
12600
--------
78624
========

Before the days of calculators, this is the way that we had
to multiply on an adding machine... hope that this gets you
started.

Buck

p.s. Geezzz! did I date myself a little or what...

[Buck Buchanan]

The column of numbers in my previous post should be right
justified... I didn't realize that the msg base would move
everything over to the left... grrr! computers and their
formatting.

Buck

[Wayne Diamond]

Buck, use [ code ] and [ /code ] statements (without any spaces) to format with fixed-width fonts, eg:

sweet huh?  [img]http://www.powerbasic.com/support/forums/smile.gif[/img]

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[Steve Hutchesson]

Thats a rather cute technique Buck, I will have to remember that
one for integer multiplication in assembler as multiply is very
slow in integer instructions.

Regards,

[email protected]

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[John Petty]

Hutch
Only looks cute in decimal, shift and add if 1 is how its done in most CPU's unless the have a dedicated flash multiplier.
The only reason the standard instruction would be slow is due to using 2 registers for the result.
Pity Intel doesnt have an instruction which does an integer multiply resulting with a long in EAX



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[Buck Buchanan]

Wayne,

Use " [ code ] and [ /code ] ", you say... hmmm.... very
intuitive. Wonder why I didn't think of that...

Buck

[Lance Edmonds]

Those, and the other UUB formatting options for the BBS, are detailed at http://www.powerbasic.com/support/forums/ubbcode.html which appears in a link next to all "reply" boxes...

Likewise, the smilies legend can be found at: http://www.powerbasic.com/support/forums/smilies.html

I hope this helps!


------------------
Lance
PowerBASIC Support
mailto:[email protected][email protected]</A>

[Steve Hutchesson]

You are probably right John, I do a quick & dirty int multiply
this way,

IntMul proc source :DWORD,multiplier :DWORD
  
    LOCAL var1 :DWORD
  
    fild source         ; load source
    fild multiplier     ; load multiplier
    fmul                ; multiply source by multiplier
    fist var1           ; store result in variable
    mov eax, var1
  
    ret
  
IntMul endp

It translates directly to PowereBASIC inline with no problems.

Still, ther are a lot of the old timer tricks that are worth
knowing so Bucks technique may be of some use when approaching
integer multiply without FP instructions.

Regards,

[email protected]

[/CODE]

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[This message has been edited by Steve Hutchesson (edited March 30, 2001).]