The very last section of Numerical Recipes in C is devoted to arbitrary
precision arithmetic.  Their code is based on stuff Knuth wrote and =
other
libraries that they provide.  An on-line version of the book can be =
found at
http://www.nr.com.

You should be able to look at their code a simplify it for the 24-bit =
functions
that you care about.

If you want to carry less baggage, but do more of your own coding, I =
have a
library for arbitrary length arrays of bits at:
http://michael.dipperstein.com/bitlibs/

It includes Increment, Decrement, Shift, And, Or, Xor, and Not =
functions.  I
keep thinking about extending it to include more arithmetic functions.  =
I have
yet to do it, but your welcome to have a go at it.

The code size could be greatly reduced if only 24-bit arrays were =
supported.

-Mike

-----Original Message-----
From: pic microcontroller discussion list =
[mailto:PICLIST@MITVMA.MIT.EDU] On
Behalf Of Andre Miller
Sent: Thursday, April 01, 2004 4:09 AM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [PIC:] Microchip C18, or HI-TECH PICC18?


=20
That's a great idea. Do you perhaps have some sample code to =
demonstrate this?
It will be much appreciated :-)

Say for example I want a 24 bit signed variable, using a struct for =
storage, how
would I:

Decrement that value
Compare it in an 'if' statement?

I can see how I would do it using a pointer to the struct, but wouldn't =
the
storage for the pointer negate the space saved by using a 3 byte =
struct?

Sorry if this is a stupid question, I know C (or I think I do), but are
relatively new to PIC's and the need to save as much RAM as possible. =
Using C on
a PC with 512MB of RAM this is less of an issue ;-).

  _____ =20

Andr=E9 Miller =09

-----Original Message-----
From: pic microcontroller discussion list =
[mailto:PICLIST@MITVMA.MIT.EDU] On
Behalf Of Gerhard Fiedler
Sent: 01 April 2004 01:33 PM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [PIC:] Microchip C18, or HI-TECH PICC18?

>>Have you ever found you needed a 24 bit integer datatype and wished
>>PICC had support for it?
>
> Frequently. There are many cases where 16 bits isn't quite enough but =

> 32
is wasteful.
> Probably less of an issue on the PIC18, but on the 16 series, RAM is
> usually the first thing you run out of.

For me that's "sometimes". In those cases I use 3 byte structs for =
storage and
the built-in 32 bit routines for the calculations. I've never had a =
case where
the additional resources that were needed to do the 32 bit calculations =
(temp
register, instruction cycles) were a problem.

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