wineport: Add support for ctz().

[Adam Martinson]

On 03/16/2011 08:34 AM, Alexandre Julliard wrote:
> Adam Martinson<amartinson at codeweavers.com>  writes:
>
>> @@ -239,6 +243,19 @@ extern int getopt_long_only (int ___argc, char *const *___argv,
>>   int ffs( int x );
>>   #endif
>>
>> +#if defined(__GNUC__)&&  (GCC_VERSION>= 30406)
>> +    #define ctz(x) __builtin_ctz(x)
>> +#elif defined(__GNUC__)&&  (defined(__i386__) || defined(__x86_64__))
>> +    static inline int ctz( unsigned int x )
>> +    {
>> +        int ret;
>> +        __asm__("bsfl %1, %0" : "=r" (ret) : "r" (x));
>> +        return ret;
>> +    }
>> +#else
>> +    #define ctz(x) (ffs(x)-1)
>> +#endif
> There's no reason to add this. Just use ffs().
>
If I thought ffs() was adequate, I would.  I need this for iterating 
sparse bitsets.

__builtin_ctz() compiles to:
mov    0x8(%ebp),%eax
bsf    %eax,%eax

(ffs()-1) compiles to:
mov    $0xffffffff,%edx
bsf    0x8(%ebp),%eax
cmove  %edx,%eax
add    $0x1,%eax
sub    $0x1,%eax

... Fortunately -O2 catches the add/sub.  So yes, there is a reason, 
ctz() is at least 50% faster.