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Rif: RE: Mathematical function long x long / long

Started by Unknown November 11, 2002

It's simple to show that

A * (B % C) can overflow!

For example if :
A = 214751
B = 10000
C = 30000

214751 * 30000 = 0x1800134d0

Is it right ?

Regards,
Giuliano
"Harrold Spier"

<harrold.spier@al Per: <>,

tium.nl> <>

Cc:

07/11/02 16.39 Oggetto: RE: [motoroladsp]
Mathematical function long x
long / long

Try:

D = A * (B / C) + /* Main part */
(A * (B % C)) / C; /* Correction with remainder */

Harrold -----Original Message-----
From: [mailto:]
Sent: Thursday, November 07, 2002 15:41
To:
Subject: [motoroladsp] Mathematical function long x long / long Does anyone have implemented a mathematical function to perform D = A *
B / C where A,B,C,D are "signed long" ? Obviusly A * B resualt can
exceed long size value. Thanks, Giuliano _____________________________________
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It's simple to show that

D = A * B / C

can overflow no matter how you calculate it if the conditions are
right.
---
A = 0x7FFF FFFF
B = 0x7FFF FFFF
C = 0x1

will never fit in a signed long D, does D have to be a signed long?

Jacob

--- In motoroladsp@y..., giuliano.to@q... wrote:
>
> It's simple to show that
>
> A * (B % C) can overflow!
>
> For example if :
> A = 214751
> B = 10000
> C = 30000
>
> 214751 * 30000 = 0x1800134d0
>
> Is it right ?
>
> Regards,
> Giuliano

> "Harrold
Spier"

> <harrold.spier@al Per:
<giuliano.to@q...>,
> tium.nl>
<motoroladsp@y...>
>
Cc:
> 07/11/02 16.39 Oggetto: RE:
[motoroladsp] Mathematical function long x
> long /
long
>

>
> Try:
>
> D = A * (B / C) + /* Main part */
> (A * (B % C)) / C; /* Correction with
remainder */
>
> Harrold > -----Original Message-----
> From: giuliano.to@q... [mailto:giuliano.to@q...]
> Sent: Thursday, November 07, 2002 15:41
> To: motoroladsp@y...
> Subject: [motoroladsp] Mathematical function long x long / long > Does anyone have implemented a mathematical function to perform D =
A *
> B / C where A,B,C,D are "signed long" ? Obviusly A * B resualt can
> exceed long size value. Thanks, Giuliano > _____________________________________
> Note: If you do a simple "reply" with your email client, only the
author
> of this message will receive your answer. You need to do a "reply
all"
> if you want your answer to be distributed to the entire group.
>
> _____________________________________
> About this discussion group:
>
> To Join: motoroladsp-subscribe@y...
>
> To Post: motoroladsp@y...
>
> To Leave: motoroladsp-unsubscribe@y...
>
> Archives: http://www.yahoogroups.com/group/motoroladsp
>
> More Groups: http://www.dsprelated.com/groups.php3 > ">http://docs.yahoo.com/info/terms/