Re: [bug-diffutils] Multithreading support?

[Paul Eggert]

Thanks, I think I found a culprit: GCC doesn't optimize 'long long'
words well for x86, for cmp.  I installed this patch, which should
make 'cmp' I/O-bound on your platform:

>From 43c2c0fd6ceedccd5a717ae0de3b1fcf857d27d9 Mon Sep 17 00:00:00 2001
From: Paul Eggert <address@hidden>
Date: Mon, 12 Aug 2013 16:24:01 -0700
Subject: [PATCH] cmp: tune 'cmp a b' for GCC x86
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Performance problem reported by David Balažic in:
http://lists.gnu.org/archive/html/bug-diffutils/2013-08/msg00013.html
* src/system.h (word): Make it size_t, not uintmax_t.
This sped up plain cmp 90% on my tests (GCC 4.8.1, x86).
---
 src/system.h | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/system.h b/src/system.h
index 827df96..f39fff0 100644
--- a/src/system.h
+++ b/src/system.h
@@ -119,10 +119,12 @@ int strcasecmp (char const *, char const *);
 #include "propername.h"
 #include "version.h"
 
-/* Type used for fast comparison of several bytes at a time.  */
+/* Type used for fast comparison of several bytes at a time.
+   This used to be uintmax_t, but changing it to size_t
+   made plain 'cmp' 90% faster (GCC 4.8.1, x86).  */
 
 #ifndef word
-# define word uintmax_t
+# define word size_t
 #endif
 
 /* The integer type of a line number.  Since files are read into main
-- 
1.7.11.7