[uml-devel] Introducing new bugs with fixups - one safe story

[Blaisorblade <blaisorblade@yahoo.it>]

One nice day a clumsy programmer (let's say me) on a "call for fixing" day 
wrote the following patch (host_kern.c):

-       start = (long long) (page->index << PAGE_CACHE_SHIFT) + from;
+       start = ((long long) page->index) << PAGE_CACHE_SHIFT + from;

to make sure page->index was casted before shifting, to avoid losing 
information. But look below. Does the new line:

        start = ((long long) page->index) << PAGE_CACHE_SHIFT + from;

must be interpreted as:

        start = (((long long) page->index) << PAGE_CACHE_SHIFT) + from;
(what I meant) or as 
        start = ((long long) page->index) << (PAGE_CACHE_SHIFT + from);

?

This message is given as help:

  CC [M]  fs/hostfs/hostfs_kern.o
/home/paolo/Admin/kernel/6/VCS/linux-2.6.git/fs/hostfs/hostfs_kern.c: In 
function `hostfs_commit_write':
/home/paolo/Admin/kernel/6/VCS/linux-2.6.git/fs/hostfs/hostfs_kern.c:504: 
warning: suggest parentheses around + or - inside shift

Luckily, however, the clumsy programmer saw the message and learned The Way 
(tm). And the patch hadn't been merged yet. Another point for GCC.
-- 
Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894)
http://www.user-mode-linux.org/~blaisorblade

		
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