Messages in this thread | | | From | "Alexander van Heukelum" <> | Subject | Re: [PATCH] asm-generic/bitops/fls64.h | Date | Tue, 13 May 2008 15:24:13 +0200 |
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On Tue, 13 May 2008 16:29:04 +0400, "Nickolay Vinogradov" <nickolay@protei.ru> said: > Alexander van Heukelum пишет: > > > Hi Nickolay, > > > > The change is ok, I guess, but the cast should be a no-op (fls > > takes an int, which is always 32 bit in linux). What is the problem > > you are seeing? Does fls64() return a wrong value in some cases? If > > so, what cpu? Which values? > > > > Why would this be a bug on big endian systems only? There is no > > pointer magic involved, so the compiler should take care of the > > casts in a correct way. > > > > Maybe you see a compiler warning? Which compiler version? > > > > (also note that current (development) kernels now have separate > > versions for 32-bit and 64-bit environments.) > > Because fls() is a macro for asm-arm: > > #define fls(x) \ > ( __builtin_constant_p(x) ? constant_fls(x) : \ > ({ int __r; asm("clz\t%0, %1" : "=r"(__r) : "r"(x) : "cc"); > 32-__r; }) ) > > We can fix it right here: > > diff --git a/include/asm-arm/bitops.h b/include/asm-arm/bitops.h > index 5c60bfc..ce3fb6f 100644 > --- a/include/asm-arm/bitops.h > +++ b/include/asm-arm/bitops.h > @@ -279,7 +279,7 @@ static inline int constant_fls(int x) > > #define fls(x) \ > ( __builtin_constant_p(x) ? constant_fls(x) : \ > - ({ int __r; asm("clz\t%0, %1" : "=r"(__r) : "r"(x) : "cc"); > 32-__r; }) ) > + ({ int __r; asm("clz\t%0, %1" : "=r"(__r) : "r"((__u32)x) : > "cc"); 32-__r; }) ) > #define ffs(x) ({ unsigned long __t = (x); fls(__t & -__t); }) > #define __ffs(x) (ffs(x) - 1) > #define ffz(x) __ffs( ~(x) )
Hmm, indeed.
Maybe: ({ int __r, __x = (x); asm("clz\t%0, %1" : "=r"(__r) : "r"(__x) : "cc"); 32-__r; }) ?
This is a 32-bit machine, right? Doesn't the compiler complain about feeding a long long into a 32-bit register?
Greetings, Alexander -- Alexander van Heukelum heukelum@fastmail.fm
-- http://www.fastmail.fm - I mean, what is it about a decent email service?
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