Dennis wrote:

>So what does this all mean?
>Ok it is quite simple (simple explaination will be given) As you can see
>Andy like myself does not get any code size change, or often very little,
>where Andrew gets a large change. For most of the time Andrew is quite
>correct, a large change can be found with just the first 3 levels of
>optimisation, after this point very little. In his case the code will have
>large numbers of routines and many variables being past between functions.

Wow ... Dennis knows my code without even seeing it!  ;-)

But he is entirely correct -- The example I mention above is for a
nearly-full 16C77 (i.e. just short of 8K of code). Lots and lots of
functions, many of which pass three, even four parameters. As this was my
first large PIC C project, I do not claim to have written all my loops,
etc. in the manner which is best for minimum-size code.  But I am learning.
Said project compiles and runs on the PC ( a sim ) and the PIC, so
portability was way up there on the list of priorities.

I do look at the assembly output quite often and try to recode in C to
minimize size.  I've found, for instance, a good way to "help"  the PIC-C
compiler is to use temp auto variables when doing relatively complex
statements involving pointers on  both sides of the "=" sign. Sometimes the
expression is too complex for the compiler, but even when it isn't, I can
get a lot of speedup by pre-evaluating a variable with, say, a single level
of indirection, and then using said handle to do all subsequent,
double-level-of-indirection references.  This would be the case where
there's a pointer to a pointer to a structure which contains multiple
fields which get operated on "simultaneously."

As I recall, the 1st-3rd (or was it 1st-5th?) levels of optimization made a
big difference, going higher made no difference at all.

PIC-C rocks!  (Thanks Clyde!)


 ___________________________________________
| Andrew E. Kalman, Ph.D.   aek@netcom.com  |
|        standard disclaimers apply         |
|___________________________________________|