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To: Inaky Perez-Gonzalez <inaky.perez-gonzalez@intel.com>
Cc: alan@lxorguk.ukuu.org.uk, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] include/asm-ARCH/page.h:get_order() Reorganize and optimize
References: <E18BmqO-0000Za-00@milikk>
From: Falk Hueffner <falk.hueffner@student.uni-tuebingen.de>
Date: 13 Nov 2002 12:45:33 +0100
In-Reply-To: <E18BmqO-0000Za-00@milikk>
Message-ID: <87y97xhew2.fsf@student.uni-tuebingen.de>
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Inaky Perez-Gonzalez <inaky.perez-gonzalez@intel.com> writes:

>     s = --s >> PAGE_SHIFT;

This code has undefined behaviour.

>     if (likely (s) < s)

What is that supposed to do?

BTW, I just noticed

#define likely(x)       __builtin_expect((x),1)

I think this should rather be

#define likely(x)       __builtin_expect((x)!=0,1)

So people can write

if (likely(pointer))

and indeed some people seem to assume that already.

--- linux-2.5.47/include/linux/compiler.h~      2002-11-11 04:28:25.000000000 +0100
+++ linux-2.5.47/include/linux/compiler.h       2002-11-13 12:44:05.000000000 +0100
@@ -10,7 +10,7 @@
 #define __builtin_expect(x, expected_value) (x)
 #endif
 
-#define likely(x)      __builtin_expect((x),1)
+#define likely(x)      __builtin_expect((x)!=0,1)
 #define unlikely(x)    __builtin_expect((x),0)
 
 /* This macro obfuscates arithmetic on a variable address so that gcc

-- 
	Falk
-
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