On Mar 27, 2013, at 4:47 AM, Peter Bigot wrote:
> is the code actually wrong?
Good question. I can't tell just by looking at it, you can't tell either.
I don't think that is a good thing, especially since there is an "obvious"
translation that looks just as efficient. I'll have to analyze more…
It does look like a newer avr-gcc creates very similar code, so it is probably
some gcc-level optimization rather than something msp430 specific. (Terrific;
I'll try to see which incomprehensibly-defined -f option controls this
optimization. Sigh.)
It looks like it's doing
// mysteriously initialize temp
for() {
if (pwmx + temp < 0)
led_xxx_off;
:
temp = temp + -1;
}
which will be correct, and probably even better on a truly RISCy CPU (no
immediate math, no decrement instruction), but it sure looks weird with a
typical microcontroller instruction set.
BillW
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