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    SubjectRe: [RFC] div64_64 support
    > I thought the motivation for div64() was that a 64:32->32 divide could 
    > be done a lot faster on a number of platforms (including the important
    > x86) than a generic 64:64->64 divide, but gcc doesn't handle the
    > devolution automatically -- there is no such libgcc function.

    That there's no such function in libgcc doesn't mean GCC
    cannot handle this; libgcc is a bunch of library functions
    that are really needed for generated code (because you
    really don't want to expand those functions inline
    everywhere) -- you won't find an addsi3 in libgcc either.

    There does exist a divmoddisi4, sort of.

    It used to be defined in three GCC targets, but commented
    out in all three. The NS32k is long gone. For Vax, a
    comment says the machine insn for this isn't used because
    it is just too slow. And the i386 version is disabled
    because it returns the wrong result on overflow (not the
    truncated 64-bit result, required by the implicit cast
    to 32-bit, but the i386 arch traps to the overflow handler).

    The only way to express the semantics you want in (GNU) C
    is to use asm() -- and that's exactly what div64() does :-)

    Blame it on the C language, but not on GCC. Not this time.


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      Last update: 2007-02-27 04:49    [W:0.019 / U:16.572 seconds]
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