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Date: Wed, 21 May 2008 12:48:52 +0200 From: Peter Zijlstra <a.p.zijlstra@...llo.nl> To: Peter 1 Oberparleiter <Peter.Oberparleiter@...ibm.com> Cc: Andrew Morton <akpm@...ux-foundation.org>, Harvey Harrison <harvey.harrison@...il.com>, linux-kernel@...r.kernel.org Subject: Re: [PATCH] consolidate all within() implementations On Wed, 2008-05-21 at 12:33 +0200, Peter 1 Oberparleiter wrote: > Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote on 21.05.2008 12:04:26: > > > +static inline int addr_within_len(const void *addr, const void > *start, > > > + size_t len) > > > +{ > > > + return ((unsigned long) addr >= (unsigned long) start) && > > > + ((unsigned long) addr < ((unsigned long) start + len)); > > > +} > > > > might be my braindamage, but I'd have written it like: > > > > static inline int > > addr_within_len(const void *addr, const void *start, size_t len) > > { > > return (unsigned long)addr - (unsigned long)start < len; > > } > > Definitely another way to put it. In my opinion the intention of the > implementation is more easily understood though when spelling it out > as (a>=b) && (a<c). peter@...py:~/tmp$ cat cmp.c int within_len1(const void *addr, const void *start, unsigned long len) { return (unsigned long)addr - (unsigned long)start < len; } int within1(const void *addr, const void *start, const void *end) { return within_len1(addr, start, (unsigned long)end - (unsigned long)start); } peter@...py:~/tmp$ cat cmp2.c int within_len2(const void *addr, const void *start, unsigned long len) { return ((unsigned long) addr >= (unsigned long) start) && ((unsigned long) addr < ((unsigned long) start + len)); } int within2(const void *addr, const void *start, const void *end) { return ((unsigned long) addr >= (unsigned long) start) && ((unsigned long) addr < ((unsigned long) end)); } peter@...py:~/tmp$ gcc -S -Os cmp*.c peter@...py:~/tmp$ ls -la cmp*.o -rw-r--r-- 1 peter peter 752 2008-05-21 12:43 cmp2.o -rw-r--r-- 1 peter peter 743 2008-05-21 12:43 cmp.o Also look at the .s output and notice mine doesn't have any additional branches ;-) > > static inline int > > addr_within(const void *add, const void *start, const void *end) > > { > > return addr_within_len(addr, start, > > (unsigned long)end - (unsigned long)start); > > } > > For empty ranges (start > end), this produces different (less expected) > results than the previous version. agreed, do we care about those? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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