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Date: Sun, 4 Jun 2006 13:18:24 -0700
From: Andrew Morton <akpm@osdl.org>
To: Wu Fengguang <wfg@mail.ustc.edu.cn>
Cc: linux-kernel@vger.kernel.org, nickpiggin@yahoo.com.au
Subject: Re: [minor fix] radixtree: regulate tag get return value
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On Sun, 4 Jun 2006 19:17:54 +0800
Wu Fengguang <wfg@mail.ustc.edu.cn> wrote:

> > test_bit() is (sadly) defined to return 0 or 1.  Did this really make a difference?
> 
> Interesting. I got the following gdb outputs. Note that tag_get()
> returns -1 and root_tag_get() returns 1048576.
> 
> (gdb) n
> 399             while (height > 0) {
> (gdb) n
> 402                     offset = (index >> shift) & RADIX_TREE_MAP_MASK;
> (gdb)
> 403                     if (!tag_get(slot, tag, offset))
> (gdb)
> 404                             tag_set(slot, tag, offset);
> (gdb) p tag_get(slot, tag, offset)
> $14 = 0
> (gdb) n
> 405                     slot = slot->slots[offset];
> (gdb) p tag_get(slot, tag, offset)
> $15 = -1

You trust gdb more than I do ;)  It's doing a pretty tricky thing there.

test_bit() returns (1 & (expr)) - it _has_ to return 0 or 1.