On Wed, 03 Jul 2013 08:04:59 -0400, Tim Prince <n8tm@xxxxxxx> wrote: > This doesn't look to me like F77, although it contains some F66. Sorry, I write broken Fortran. > > If you are using 32-bit gfortran, the i486 code with x87 instructions is particularly prone to this kind of problem. Did you try -march=native, or, if using an extremely old CPU, -ffloat-store? > > -- > Tim Prince I am using gfortran for x86 and x86_64 and got similar problems on both. Met this problem when I used "-march=native -O4". Problem disappeared with "-march=native -O4 -ffloat-store". Thank you for mentioning "-ffloat-store". This is exactly what I was looking for. BTW, The performance impact is significant. Now I have modified my algorithm so that it does not rely on the precision given by -ffloat-store. Guan
