Greetings! I think its a matter of when the registers are written to memory. Apparently the m68k can optimize in such a way that many intermediate results are held in registers before having to be written out. There is no -ffloat-store on x86. The difference is perhaps related to the paucity of registers on x86, and the fact that m68k registers are *96* bits wide, AFAICR, instead of 80. But in general, one does get more precision on x86 FPU calculations than the strictly 64bit SSE2, for example.
Take care, Raymond Toy <[EMAIL PROTECTED]> writes: > >>>>> "Camm" == Camm Maguire <[EMAIL PROTECTED]> writes: > > Camm> Greetings! > Camm> Rick Younie <[EMAIL PROTECTED]> writes: > > >> Camm Maguire wrote: > >> > Greetings! I have one Debian machine (m68k) which is producing very > >> > small numerical discrepancies on the results of the two floating > point > >> > intensive tests in rtest8.mac: > >> > >> Hi, > >> > >> That rang a bell. There's this in the gcc man page: > >> > >> -ffloat-store > >> Do not store floating point variables in registers. This pre- > >> vents undesirable excess precision on machines such as the 68000 > >> where the floating registers (of the 68881) keep more precision > >> than a double is supposed to have. > >> > >> For most programs, the excess precision does only good, but a > >> few programs rely on the precise definition of IEEE floating > >> point. Use `-ffloat-store' for such programs. > > Camm> That did it -- thanks! As Richard Fateman observed, its quite > Camm> surprising the magnitude of the difference was so large. Apparently > Camm> m68k has the more accurate answer, right? In any case, I'm adding > Camm> -ffloat-store to gcl's compile flags on m68k to avoid testing > Camm> problems. > > But does gcl on x86 also do a -ffloat-store? x86 also keeps extra > precision, so I would have expected similar issues on x86. > > Ray > > > _______________________________________________ > Gcl-devel mailing list > [EMAIL PROTECTED] > http://mail.gnu.org/mailman/listinfo/gcl-devel > > -- Camm Maguire [EMAIL PROTECTED] ========================================================================== "The earth is but one country, and mankind its citizens." -- Baha'u'llah
