linux-kernel - Re: [PATCH] avoid negative shifts in radix-tree.c

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Message-ID: <Pine.LNX.4.64N.0708291232130.26167@blysk.ds.pg.gda.pl>
Date:	Wed, 29 Aug 2007 12:39:16 +0100 (BST)
From:	"Maciej W. Rozycki" <macro@...ux-mips.org>
To:	Christoph Hellwig <hch@...radead.org>
cc:	Peter Firefly Lund <firefly@...64.dk>,
	Christoph Lameter <clameter@....com>,
	Momchil Velikov <velco@...ata.bg>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] avoid negative shifts in radix-tree.c

On Mon, 27 Aug 2007, Christoph Hellwig wrote:

> The conceptual change looks fine to me, but the code looks a little odd,
> what about:
> 
> static __init unsigned long __maxindex(unsigned int height)
> {
> 	unsigned int tmp = height * RADIX_TREE_MAP_SHIFT;
> 	int shift = RADIX_TREE_INDEX_BITS - tmp;
> 
> 	if (shift < 0)
> 		return ~0UL;
> 	return ~0UL >> shift;
> }
> 
> instead?

 This patch has been successfully tested on actual hardware (VAXstation 
4000/90).  If nobody objects, I'll push it to Andrew.

  Maciej

Signed-off-by: Maciej W. Rozycki <macro@...ux-mips.org>

patch-vax-2.6.17-rc4-20070111-radix-maxindex-0
diff -up --recursive --new-file linux-vax-2.6.17-rc4-20070111.macro/lib/radix-tree.c linux-vax-2.6.17-rc4-20070111/lib/radix-tree.c
--- linux-vax-2.6.17-rc4-20070111.macro/lib/radix-tree.c	2006-10-31 19:05:50.000000000 +0000
+++ linux-vax-2.6.17-rc4-20070111/lib/radix-tree.c	2007-01-22 01:24:17.000000000 +0000
@@ -825,9 +825,11 @@ radix_tree_node_ctor(void *node, kmem_ca
 static __init unsigned long __maxindex(unsigned int height)
 {
 	unsigned int tmp = height * RADIX_TREE_MAP_SHIFT;
-	unsigned long index = (~0UL >> (RADIX_TREE_INDEX_BITS - tmp - 1)) >> 1;
+	unsigned long index;
 
-	if (tmp >= RADIX_TREE_INDEX_BITS)
+	if (tmp < RADIX_TREE_INDEX_BITS)
+		index = (~0UL >> (RADIX_TREE_INDEX_BITS - tmp - 1)) >> 1;
+	else
 		index = ~0UL;
 	return index;
 }
-
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