On 03/25/2013 11:42 AM, Paolo Bonzini wrote:
>
>>>>> +size_t buffer_find_nonzero_offset(const void *buf, size_t len)
>>>>> +{
>>>>> + VECTYPE *p = (VECTYPE *)buf;
>>>>> + VECTYPE zero = ZERO_SPLAT;
>>>>> + size_t i;
>>>>> +
>>>>> + assert(len % (BUFFER_FIND_NONZERO_OFFSET_UNROLL_FACTOR
>>>>> + * sizeof(VECTYPE)) == 0);
>>>>> + assert(((uintptr_t) buf) % sizeof(VECTYPE) == 0);
>>>>> +
>>>>> + if (*((const long *) buf)) {
>>>>> + return 0;
>>>>> + }
>>>>> +
>>>>> + for (i = 0; i < len / sizeof(VECTYPE);
>>>> Why not put len/sizeof(VECTYPE) in a variable?
>>>
>>> are you afraid that there is a division at each iteration?
>>>
>>> sizeof(VECTYPE) is a power of 2 so i think the compiler will
>>> optimize it
>>> to a >> at compile time.
>> true, but it still is done every iteration.
>
> len is an invariant, the compiler will move it out of the loop
> automatically. Write readable code unless you have good clues
> that it is also slow.
>
I know it does for x86 but I wasn't sure for other platforms.
I'm fine with as is.
Orit
> Paolo
>
