Re: gzip use of memcpy

[Jim Meyering]

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 <address@hidden>
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