Thanks for the helpful information, David. Oddly, -ffloat-store doesn't seem to make any difference:
[c:\projects\threads]gcc -ffloat-store -o thread1 thread1.c -lpthread [c:\projects\threads]thread1 Main: t/1+t = 0.0005609048868329022342546 Thread 0: t/1+t = 0.0005609048868329021258344 Thread 1: t/1+t = 0.0005609048868329021258344 Thread 2: t/1+t = 0.0005609048868329021258344 Thread 3: t/1+t = 0.0005609048868329021258344 -----Original Message----- From: Billinghurst, David (RTATECH) [mailto:[EMAIL PROTECTED] Sent: Sunday, August 03, 2008 10:16 PM To: Richard Stanton Subject: RE: cygwin gcc: Different numerical results in thread vs in main() Try compiling with -ffloat-store then report back. google for "float-store excess precision gcc" to understand why this may help. I don't recommend -ffloat-store as a fix, but it can help diagnose the problem. David > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Richard Stanton > Sent: Monday, 4 August 2008 15:03 > To: cygwin@cygwin.com > Subject: cygwin gcc: Different numerical results in thread vs in > main() > > The following program performs exactly the same calculation 5 times, > once inside main(), and again in 4 thread functions. > Though the calculations are identical, the results are not. > When I compile and run the same program on my Mac, all the results are > identical. By the way, this is using the latest gcc 3.4.4. > > Richard Stanton > > ------------------ > > [c:\projects\threads]thread1 > Main: t/1+t = 0.0005609048868329022342546 > Thread 0: t/1+t = 0.0005609048868329021258344 > Thread 1: t/1+t = 0.0005609048868329021258344 > Thread 2: t/1+t = 0.0005609048868329021258344 > Thread 3: t/1+t = 0.0005609048868329021258344 > > > #include <stdio.h> > #include <pthread.h> > > #define NUM_THREADS 4 > > double t = 0.0005612196776927068104374; > > void * thread_function (void *arg) > { > int i; > int id = *((int *)arg); > > printf("Thread %d: t/1+t = %30.25lf\n", id, t/(1.0+t)); > > return NULL; > } > > > int main() > { > int i; > int arg[NUM_THREADS] = {0,1,2,3}; > pthread_t thread[NUM_THREADS]; > pthread_attr_t attr; > > printf("Main: t/1+t = %30.25lf\n", t/(1.0+t)); > > /* initialize and set the thread attributes */ > pthread_attr_init( &attr ); > pthread_attr_setdetachstate( &attr, PTHREAD_CREATE_JOINABLE ); > > /* creating threads */ > for ( i=0; i<NUM_THREADS; i++ ) { > if ( pthread_create( &thread[i], &attr, thread_function, > (void *)&arg[i] )) { > fprintf(stderr,"Creating thread %d failed!",i); > return 1; > } > } > > /* joining threads (== waiting for them to exit) */ > for ( i=0; i<NUM_THREADS; i++ ) { > if ( pthread_join ( thread[i], NULL ) ) { > fprintf(stderr,"Joing thread %d failed!",i); > return 1; > } > } > > return 0; > } -- Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple Problem reports: http://cygwin.com/problems.html Documentation: http://cygwin.com/docs.html FAQ: http://cygwin.com/faq/
