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Subject: Re: do_div considered harmful
Date: Mon, 4 Aug 2003 11:46:52 +0200 (MEST)	[thread overview]
Message-ID: <> (raw)

> Sometimes the slash-star operator comes in handy.

Certainly an improvement. Maybe it will help a little.

But really, do_div is not a C function, it has very
nonintuitive behaviour.
The two bugs are: (i) the name is wrong, it returns a
remainder but the name only talks about dividing, and
(ii) worst of all, it changes its first argument.

> + * uint32_t do_div(uint64_t *n, uint32_t base)

And the comment that you added, copied from elsewhere,
is confusing too. The first parameter is not uint64_t *.
This thing cannot be described in C.

I would still like to replace do_div by DO_DIV_AND_REM
as a big fat warning - this is a macro, read the definition.
And the common case, where no remainder is used, by DO_DIV
#define DO_DIV(a,b)	(void) DO_DIV_AND_REM(a,b)


[Perhaps DO_DIV64, to also indicate a type.]

[The same problem happens with sector_div. I recall having
to fix sector_div calls in scsi code. These functions are
bugs waiting to happen. Nobody expects that after
	res = func(a,b);
the value of a has changed.]

             reply	other threads:[~2003-08-04  9:46 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2003-08-04  9:46 Andries.Brouwer [this message]
  -- strict thread matches above, loose matches on Subject: below --
2003-08-04  5:31 do_div considered harmful Steve French
2003-08-04  2:03 Andries.Brouwer
2003-08-04  2:29 ` Andrew Morton
2003-08-04  5:54 ` Linus Torvalds

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