svn commit: r187693 - head/sys/kern
jroberson at jroberson.net
Sun Jan 25 11:16:40 PST 2009
On Sun, 25 Jan 2009, Christoph Mallon wrote:
> Jeff Roberson schrieb:
>> On Sun, 25 Jan 2009, Jeff Roberson wrote:
>>> Author: jeff
>>> Date: Sun Jan 25 18:38:42 2009
>>> New Revision: 187693
>>> URL: http://svn.freebsd.org/changeset/base/187693
>>> - bit has to be fd_mask to work properly on 64bit platforms. Constants
>>> must also be cast even though the result ultimately is promoted
>>> to 64bit.
>>> - Correct a loop index upper bound in selscan().
>> Sorry about that, should've tested my earlier patch for more than a couple
>> of days. I seldom remember c's integer promotion rules as they relate to
>> constants. You'd think they'd make it easy on us and just promote it to
>> the largest type in the expression/lvalue. I'm not sure why they don't.
>> Perhaps the more careful among you knows the answer.
> The rule for operations is quite simple: An operation never cares for the
> type of its user. It only uses the type of the operand(s) to determine its
> result type. So for a = b + c the type of the result of + only depends on the
> types of b and c, but never on a.
> Integer literals have a bit ugly rules what type they are: It depends on the
> base (!) and on the magnitude of the literal.
> If in doubt and you need a specific type (and maybe making it more clear for
> a reader) then cast.
I'm familiar with the rule, what I don't know is the rationale. It
would've been much more convenient if they did care for the user.
In what case does the base matter? If you use a literal large enough the
compiler conveniently complains. However, in this case the shift value
was computed and applied to 1 which overflowed before being assigned to a
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