Messages in this thread | | | Date | Sun, 31 Aug 2003 15:48:19 -0700 (PDT) | From | Linus Torvalds <> | Subject | Re: [PATCHSET][2.6-test4][0/6]Support for HPET based timer - Take 2 |
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On Sun, 31 Aug 2003, Erik Andersen wrote: > > Been there done that, got the scars to prove it. do_div() is a > macro that acts sortof like the ISO C99 lldiv(3) function.
No.
You missed a very important part of do_div() - it has _totally_ different numerical range than a regular /, % or lldiv() call.
All of /, % and lldiv() work on 64-bit numbers. do_div() DOES NOT!
do_div() very much is all about:
*** 32-bit divisor ***
which also implies that the remainder is 32-bit.
And the fact is, such a division is a lot faster than a full 64-bit division. On a _lot_ of architectures, but notably so on x86.
It is _not_ a 64-bit divide, and that's not only important, it's the whole _reason_d'etre_ for the whole function. See?
So by continually confusing it with a 64-bit divide (either by confusing it with lldiv() or those horrible gcc internal __{div|mod}di3u things), you miss the whole point of the function.
Linus
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