hi Dave: Thanks for your kind reply. 2011/5/20 Dave Hylands <dhylands@xxxxxxxxx>: > Hi lody, > > On Thu, May 19, 2011 at 8:34 PM, loody <miloody@xxxxxxxxx> wrote: >> hi all: >> My platform is 32-bits cpu and I need following calculation in my driver. >> #define longdiv(sr1, sr2, div) (unsigned long )((((unsigned long >> long)(sr1) << 32) ^ (sr2)) / (div)) >> >> my question are: >> 1. why "__udivdi3" has any relationship with above calculation? > > Because you're doing 64 bit arithmetic (unsigned long long) and 64 bit > division is not supported in all kernels. why the name "__udivdi3" has relation to 64-bits arighmetic? Why linker ask for "__udivdi3", it seems there is a common sense for linker that when doing 64-bits calculation it will try to find "__udivdi3", am i right? > >> 2. I know the above calculation is implemented in clibc, but why >> kernel still implement itself? >> why kernel try to make another wheel instead of including what >> clib provided ? > > The kernel doesn't use anything from the C runtime library at all. > > 64-bit division and floating point are 2 things not supported in the > kernel, although they do happen to word on some platforms, they aren't > portable operations. > the 64-bit division seem supported in gcc toolchain, and gcc will take care the platform issue when we cross-compile the gcc, right? It should be safe to static link the 64bits division in gcc. -- Regards, _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
