Hi Pieter! This could be complete misinformation, or correct but not relevant.
On Thu, Jan 15, 2015 at 12:57 PM, <pbed...@aol.com> wrote: > I wrote a test program in fortran and used gfortran 4.9.2 (tdm64-gcc 4.9.2) > ... > However for extended floating point precision off-diagonal elements of the > identity matrix for thread 0 are <> 0 with the expected magnitude, for > threads 1 to 3 they are a factor 1000 (!) larger and moreover identical to > those of the identity matrix in the double floating point precision > calculation. > ... > Where is the error? I have a vague recollection of a discussion (probably on this list) about start-up code writing the Intel x87 floating-point control word to the floating-point processor. This was maybe something about setting a mode where extended precision (80-bit) was degraded to double precision (64-bit). If any of this is right (and not just a figment of my imagination), there was some talk of the floating-point control word start-up code getting called at thread start-up, so that even if your own initialization code in your main thread wrote the desired floating-point control word (e.g., to enable extended precision), this setting would not apply to other threads because they would get initialized with some default control word (hypothetically setting those threads to non-extended double precision). Again, this is a long shot, but I do seem to recall some discussion of floating-point control word start-up code from a month or two ago. > With regards > Pieter Bedijn - retired scientist and software developer Good luck. K. Frank ------------------------------------------------------------------------------ Dive into the World of Parallel Programming. The Go Parallel Website, sponsored by Intel and developed in partnership with Slashdot Media, is your hub for all things parallel software development, from weekly thought leadership blogs to news, videos, case studies, tutorials and more. Take a look and join the conversation now. http://goparallel.sourceforge.net/ _______________________________________________ Mingw-w64-public mailing list Mingw-w64-public@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/mingw-w64-public
