Weddington, Eric wrote:
-----Original Message----- From:
avr-gcc-list-bounces+eweddington=cso.atmel....@nongnu.org
[mailto:avr-gcc-list-bounces+eweddington=cso.atmel....@nongnu. org]
On Behalf Of David VanHorn Sent: Wednesday, February 25, 2009 9:05
AM To: avr-gcc-list@nongnu.org Subject: [avr-gcc-list] Newbie
question
<snip>
467: if ((TIFR & (1<< TOV1))==1) // If we rolled T0
+00000253: B788 IN R24,0x38 In from I/O
location +00000254: 2799 CLR R25 Clear
Register +00000255: 7084 ANDI R24,0x04 Logical
AND with immediate +00000256: 7090 ANDI R25,0x00
Logical AND with immediate +00000257: 9701 SBIW
R24,0x01 Subtract immediate from word +00000258: F421
BRNE PC+0x05 Branch if not equal
Hmm. It seems the compiler is treating this expression as a 16-bit
value. It could be because of the comparison with the constant '1',
which gets automatically treated like an int. Can you see if
typecasting will help?:
if ((TIFR & (uint8_t)(1<<TOV1)) == (uint8_t)1)
If it works, it should save 2 instructions.
(This reply is really to David VanHorn, rather than Eric.)
I'd be surprised if either the original code or your modified code
actually works - since TOV1 is 2, the conditional can never be true.
The code you *really* want is:
if (TIFRx & (1 << TOV1)) {
You also seem to have forgotten to enable optimisation. There is no
point trying to hand-optimise your code if you don't let the compiler do
its job properly! Use "-Os" optimisation unless you have particular
reason to do anything else. Also enable compiler warnings - at a
minimum, use these flags:
-Wall -Wextra -Wunreachable-code
Then the compiler would have told you of your error here.
Also, when posting to the mailing list, it is much more helpful if you
include your actual C code (preferably a minimal compilable snippet) and
a note of your compiler version and command-line flags. That will let
others test your code and give you more help. Some people, such as me,
*like* the challenge of finding ways to get smaller and faster code for
a given function. But I don't like trying to dig C code out of the
comments of an assembling listing.
It's also not very polite to say that the compiler "irritates you no
end" - Eric and many others have spend a great deal of time and effort
writing the compiler and tools so that people like you have high quality
development tools that are free (as in "free speech") and zero cost.
The developers are always happy to listen to constructive criticism, but
your complaints should be well-grounded and politely worded.
As a newbie to C, here's a couple of tips in writing your code - use
plenty of spaces *consistently* in your code, it makes it easier to
read, and easier to search. And *always* write your if's as:
if (xxx) {
foo();
}
or
if (xxx) {
foo();
} else {
bar();
}
Do the same with for and while loops. Once you are a C expert, you'll
occasionally find the short form more appropriate :
if (xxx) foo();
But until you consider yourself an expert, using the brackets will make
your code clearer, your debugging easier, and give you fewer headaches
during code maintenance.
If you are still looking for suggestions to improve the code, post the C
code (including definitions of any globals involved), and I will happily
give more suggestions.
mvh.,
David
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