Re: [PATCH] include/asm-ARCH/page.h:get_order() Reorganize and optimize

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• In reply to: Inaky Perez-Gonzalez: "[PATCH] include/asm-ARCH/page.h:get_order() Reorganize and optimize"
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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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• Next message: Lars Marowsky-Bree: "Re: md on shared storage"
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• In reply to: Inaky Perez-Gonzalez: "[PATCH] include/asm-ARCH/page.h:get_order() Reorganize and optimize"
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