Chip Salzenberg writes:
> GCC is warning about a pointer-to-int conversion when
> the likely() and unlikely() macros are used with pointer
> values. So, for architectures where pointers are larger
> than 'int', I suggest this patch.
...
> -#define likely(x) __builtin_expect((x),1)
> -#define unlikely(x) __builtin_expect((x),0)
> +#define likely(x) __builtin_expect((x), 1)
> +#define likely_p(x) __builtin_expect((x) != 0, 1)
> +#define unlikely(x) __builtin_expect((x) ,0)
> +#define unlikely_p(x) __builtin_expect((x) != 0 ,0)
That's ugly, plus the "_p" suffix is kind of a
standard for "predicate". (__builtin_constant_p, etc.)
I'm using these in the procps project:
// tell gcc what to expect: if(unlikely(err)) die(err);
#define likely(x) __builtin_expect(!!(x),1)
#define unlikely(x) __builtin_expect(!!(x),0)
#define expected(x,y) __builtin_expect((x),(y))
That makes a slight change to the meaning, since the
original value is no longer available. I've not
found that to be any trouble at all; if it is then
you could work around it using a statement-expression
with a variable, cast, and/or __typeof__.
Something like this:
#define likely(x) ({ \
__typeof__ (x) _tmp; \
__builtin_expect(!!_tmp,1); \
_tmp; \
})
-
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This archive was generated by hypermail 2b29 : Thu Aug 07 2003 - 22:00:28 EST