On Mon, Aug 08, 2005 at 09:30:18PM +0300, Shachar Shemesh wrote: > Actually, something extremely weird it going on here. The result change, > considerably, when I compile with or without "no-math-errno":
Yeah. The no-math-errno thing seems to trigger quite a few FPU-related optimizations. > >[EMAIL PROTECTED]:/tmp$ gcc -O2 -fno-math-errno -o test -lm test.c && time > >./test > >nan > > > >real 0m7.521s > >user 0m7.517s > >sys 0m0.003s > > Why did the answer turn into "nan"? Because the variable q is garbage when the loop starts, and ends up being either garbage or overflown. Without -fno-math-errno, it's initialised to 0 before the loop begins. If you declare it with double q = 0;, you will get a meaningful answer in the -fno-math-errno case as well. The compiler isn't at fault here because it doesn't have to initialize it for you. -- avva "There's nothing simply good, nor ill alone" -- John Donne ================================================================= To unsubscribe, send mail to [EMAIL PROTECTED] with the word "unsubscribe" in the message body, e.g., run the command echo unsubscribe | mail [EMAIL PROTECTED]
