lkml.org 
[lkml]   [2003]   [Aug]   [31]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCHSET][2.6-test4][0/6]Support for HPET based timer - Take 2

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


-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2009-11-18 23:46    [W:0.060 / U:0.132 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site