For some fun I ran the equation though Proton+ the compiler I use

With T1, ZCal, T2 and T2Cal as WORD vars (unsigned longs, int16)and Y as a
FLOAT

The code space with the equation like this

y = (T1 - ((ZCal * T2) / T2Cal)) / T2Cal = 774 words

Compiling to a 18f452 reduced the code to 618 words

By splitting the equation into smaller sections (a very simple trick to save
code) like this

   y = ZCal * T2
   y = y / T2Cal
   y = (T1 - y)/ T2Cal

   with the 16f877 = 601 words
   with the 18f452 = 497 words

But if you did some scaling  (depends on the numbers you are working with)
and changed Y to a DWORD (32 bit unsigned)
the results with the same formula

   16f877 = 230 words
   18f452 =  229 words


 Tim



-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Martijn van Aartrijk
Sent: 05 June 2003 13:11
To: PICLIST@MITVMA.MIT.EDU
Subject: [PIC]: How to optimize?


Hello all,

I have this irritanting calculation which I must do on my PIC16F877, and
I'm using CCS PIC C (PCM). Trouble is, this calculation alone takes up
4% of my code space, and I want it reduced. Unfortunately, my PIC asm
isn't too good and I don't really know where to begin. I was hoping some
of you might be able to help.

The calculation includes a few calibration values (end on -Cal) and have
to do with some timing intervals.

y = (T1 - ((ZCal * T2) / T2Cal) / T2Cal;

In itself, no real shocking formula. Point is, T1, ZCal, T2 and T2Cal
are unsigned longs (int16), so their product is an int32. Result y is a
float. As you can see, the compiler generates an incredible lot of code
to handle all the int32, int16 and float stuff. So my question is: does
anyone know how to handle this more efficiently? I've been trying to
rewrite the equation but it doesn't seem to get any better.

Thanks a lot!
Martijn

PS. Yes, this is a repost, but I'm still stuck with the problem. Sorry.

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