Re: What micros do you actually hate to work with?

"Joerg" <notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx> schreef in bericht
news:ZDTWg.13298$6S3.881@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Ok, I have only used '51 family device from Atmel, don't know if there are
16-bitters in store anywhere. But your word "generally" urges me to ask
you how this multiplication by 0.457358479 (Horner + CSD optimized) would
be done in C on a uC without HW multiplier in less than 30 CPU clocks:

A very bad example. This has nothing to do with C or ASM, but shows
an example where you need to solve a problem with minimal resources.
In which case a clever approach is needed. In C, you would have to be
equally clever, so it would look more or less the same. Something like
this perhaps:

register int16 twelve;
register int16 thirteen;

.....

thirteen=twelve;
twelve=>>2;
thirteen+=twelve; // X1=X*2^-2+X
twelve=>>2;
thirteen+=twelve; // X2=X1*2^-2+X
twelve=>>4;
thirteen+=twelve; // X3=X2*2^-4+X

Etcetera.

Would compile to the same assembly code. The compiler will
optimize the shift by a constant to a number of single shifts,
no worries about that.

Generally speaking, asm is dead. Generally, using C will produce
better code in less time. Generally, with less than tiny asm
projects, a C version will give you a smaller footprint.
Generally, using asm is a waste of time and energy and
produces lower quality code.

Now that was a stupid example.

--
Thanks, Frank.
(remove 'q' and '.invalid' when replying by email)






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