Hi! On Thursday, 16. November 2006 02:56, Lubomir Bourdev wrote:
Unfortunately, the CPU itself violates rule 3: a double in a register and the same double written to memory and read back need no longer compare equal - a behavior that is really hard to debug :-(
Well, the world will never be perfect, but that doesn't mean we shouldn't strive for perfection :-) (That seems quite a serious problem though! Can you point me at a document describing this? Which CPUs are affected?)
GCC manual, section 10.8: On 68000 and x86 systems, for instance, you can get paradoxical results if you test the precise values of floating point numbers. For example, you can find that a floating point value which is not a NaN is not equal to itself. This results from the fact that the floating point registers hold a few more bits of precision than fit in a double in memory. Compiled code moves values between memory and floating point registers at its convenience, and moving them into memory truncates them. Better, here: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=323
[...] The disadvantage is that built-in types will rarely be used as GIL channels, which could have performance implications due to abstraction penalty (and I do have data to demonstrate such performance penalty exists)
I would be interested in that, where can I find it? -- Ciao, / / /--/ / / ANS