On Tue, Oct 23, 2012 at 11:14 PM, mind entropy <mindentr...@gmail.com>wrote:
> Hi,
>
> I was reading the mspgcc manual (
>
> http://www.eecs.harvard.edu/~konrad/projects/motetrack/mspgcc-manual-20031127.pdf
> )
> and on Pg 39 its written as
>
I believe there is a more up to date version but I'm not usre where it
lives. Perhaps Peter can point to it?
>
> "If you execute
> while ((long) a & 0x80000l);
> the program will hang, unless ’a’ is declared volatile. So, do it!"
>
With optimization a will be put into a register (actually two registers
since it is a long) and loaded once.
If a is declared as a volatile, that tells the toolchain that a can change
out from underneath any assumptions
made about contents. This forces the compiler to reload a into a register
each iteration.
> I did not get it. Why should it hang?
>
> Thanks,
> Gautam.
>
>
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--
Eric B. Decker
Senior (over 50 :-) Researcher
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