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From: "jb at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug fortran/29549] matmul slow for complex matrices Date: Sat, 04 Nov 2006 20:34:00 -0000 [thread overview] Message-ID: <20061104203449.8736.qmail@sourceware.org> (raw) In-Reply-To: <bug-29549-1719@http.gcc.gnu.org/bugzilla/> ------- Comment #2 from jb at gcc dot gnu dot org 2006-11-04 20:34 ------- I did some experimenting, and it seems the C version of a trivial matrix multiply program is much slower than the same program written in Fortran? Switch the commented declarations and c[i][j] = 0 in the loop to get the float version. #include <stdio.h> #include <complex.h> #include <sys/time.h> #include <time.h> int main(void) { const int n = 300; complex float a[n][n], b[n][n], c[n][n]; //float a[n][n], b[n][n], c[n][n]; int i, j, k, tc; struct timeval tv, tv2; float res; tc = 0; gettimeofday (&tv, NULL); for (i = 0; i < n; i++) { for (j = 0; j < n; j++) { c[i][j] = 0.0 + 0.0*I; //c[i][j] = 0.0; for (k = 0; k < n; k++) { // printf("i %i, j %i, k %i\n", i, j, k); c[i][j] = c[i][j] + a[i][k] * b[k][j]; tc++; } } } gettimeofday (&tv2, NULL); res = tv2.tv_sec - tv.tv_sec + (tv2.tv_usec - tv.tv_usec) / 1000000.0; printf ("gemm time: %f\n", res); printf ("trip count: %i\n", tc); } Fortran version: program mymatmul implicit none integer, parameter :: n = 300 real, dimension(n,n) :: rr, ri complex, dimension(n,n) :: a,b,c real :: t1, t2 integer :: i, j, k call random_number (rr) call random_number (ri) a = cmplx (rr, ri) call random_number (rr) call random_number (ri) b = cmplx (rr, ri) call cpu_time (t1) do j = 1, n do i = 1, n c(i,j) = cmplx (0., 0.) do k = 1, n c(i,j) = c(i,j) + a(i,k) * b(k,j) end do end do end do call cpu_time (t2) write (*,'(F8.4)') t2-t1 open (10, file="cmatrix", form='unformatted') write (10) c close (10) end program mymatmul Fortran version with real instead of complex: program mymatmul implicit none integer, parameter :: n = 300 real, dimension(n,n) :: a,b,c real :: t1, t2 integer :: i, j, k, tc call random_number (a) call random_number (b) call cpu_time (t1) tc = 0 do j = 1, n do i = 1, n c(i,j) = 0. do k = 1, n c(i,j) = c(i,j) + a(i,k) * b(k,j) tc = tc + 1 end do end do end do call cpu_time (t2) write (*,'(F8.4)') t2-t1 write (*, *) 'Trip count: ', tc open (10, file="rmatrix", form='unformatted') write (10) c close (10) end program mymatmul And my results: C version, complex: -O2 2.0 s -ffast-math 0.9 gfortran -O2: 0.32 float: -O2 0.6 s fast math makes no difference! gfortran -O2 -g 0.07 -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29549
next prev parent reply other threads:[~2006-11-04 20:34 UTC|newest] Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top 2006-10-22 15:58 [Bug fortran/29549] New: " tobias dot burnus at physik dot fu-berlin dot de 2006-11-04 14:15 ` [Bug fortran/29549] " jb at gcc dot gnu dot org 2006-11-04 20:34 ` jb at gcc dot gnu dot org [this message] 2006-11-04 21:24 ` jb at gcc dot gnu dot org 2006-11-04 22:17 ` jb at gcc dot gnu dot org 2008-02-10 19:20 ` jb at gcc dot gnu dot org 2008-02-10 22:48 ` tkoenig at gcc dot gnu dot org 2008-02-16 18:50 ` fxcoudert at gcc dot gnu dot org 2008-02-16 19:01 ` fxcoudert at gcc dot gnu dot org 2008-02-16 21:59 ` rguenth at gcc dot gnu dot org 2008-02-16 22:33 ` jb at gcc dot gnu dot org 2008-02-19 19:34 ` jb at gcc dot gnu dot org 2008-02-25 19:22 ` jb at gcc dot gnu dot org 2008-02-25 19:28 ` jb at gcc dot gnu dot org 2008-02-26 21:15 ` jb at gcc dot gnu dot org
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