Hi Jim
It would be nice to declare the delta inside the function scope.
Index: inflate.c
===================================================================
--- inflate.c (revision 248271)
+++ inflate.c (working copy)
@@ -526,6 +526,7 @@
register unsigned e; /* table entry flag/number of extra bits */
unsigned n, d; /* length and index for copy */
unsigned w; /* current window position */
+ unsigned delta; /* delta between slide+w and slide+d */
struct huft *t; /* pointer to table entry */
unsigned ml, md; /* masks for bl and bd bits */
register ulg b; /* bit buffer */
@@ -593,7 +594,9 @@
do {
n -= (e = (e = WSIZE - ((d &= WSIZE-1) > w ? d : w)) > n ? n :
e);
#if !defined(NOMEMCPY) && !defined(DEBUG)
- if (w - d >= e) /* (this test assumes unsigned
comparison) */
+ /* make the unsigned comparision in positive range. */
+ delta = w > d ? w - d : d - w;
+ if (delta >= e) /* (this test assumes unsigned
comparison) */
{
memcpy(slide + w, slide + d, e);
w += e;
Thanks
Yuxi
> -----Original Message-----
> From: Jim Meyering [mailto:j...@meyering.net]
> Sent: January 11, 2010 12:32 PM
> To: Alain Magloire
> Cc: Yuxi Zhang; bug-gzip@gnu.org
> Subject: Re: gzip use of memcpy
>
> Alain Magloire wrote:
>
> > Bonjour,
> >
> > Our tester (Yuxi) was proposing something along this line
> to check
> > for overlapping.
> >
> > ===email from yuxi===
> > We could do a smart checking here:
> > Unsigned int delta = w > d ? w -d : d -w;
> > if (delta >= e) /* (this test assumes unsigned
> > comparison) */
> > {
> > memcpy(slide + w, slide + d, e);
> > w += e;
> > d += e;
> > }
> > else /* do it slow to avoid memcpy()
> > overlap */
>
> Good idea. Thank you!
> How about the patch below?
> I realize that it introduces a c99-ism (stmt after decl), but
> experience with coreutils has shown that that is no longer a
> problem in practice.
>
> From 17822e2cab5e47d73f224a688be8013c34f990f7 Mon Sep 17 00:00:00 2001
> From: Yuxi Zhang <yzh...@qnx.com>
> Date: Mon, 11 Jan 2010 18:28:30 +0100
> Subject: [PATCH] gzip -d: use memcpy more often
>
> * inflate.c (inflate_codes): Use memcpy (rather than slower
> memcopy-like code) in more cases.
> ---
> inflate.c | 3 ++-
> 1 files changed, 2 insertions(+), 1 deletions(-)
>
> diff --git a/inflate.c b/inflate.c
> index 5b68314..75353e2 100644
> --- a/inflate.c
> +++ b/inflate.c
> @@ -589,7 +589,8 @@ int bl, bd; /* number of bits
> decoded by tl[] and td[] */
> do {
> n -= (e = (e = WSIZE - ((d &= WSIZE-1) > w ? d : w))
> > n ? n : e); #if !defined(NOMEMCPY) && !defined(DEBUG)
> - if (d < w && w - d >= e)
> + unsigned int delta = w > d ? w - d : d - w;
> + if (delta >= e)
> {
> memcpy(slide + w, slide + d, e);
> w += e;
> --
> 1.6.6.511.gf46c4
>
