Bill Davidsen wrote:
> Philippe De Muyter wrote:
>> On Tue, Feb 06, 2007 at 10:41:30PM +0200, Ahmed S. Darwish wrote:
>>> On Tue, Feb 06, 2007 at 09:52:17AM -0800, Joe Perches wrote:
>>>> On Tue, 2007-02-06 at 18:04 +0200, Ahmed S. Darwish wrote:
>>>>> A patch to use ARRAY_SIZE macro already defined in kernel.h
>>>>> Signed-off-by: Ahmed S. Darwish <[email protected]>
>>> [...]
>>>>> - int nelem = sizeof(procfsentries)/sizeof(procfsentries[0]);
>>>>> + int nelem = ARRAY_SIZE(procfsentries);
>>>>> int i;
>>>>>
>>>>> for (i=0; i < nelem; i++) {
>>>> For these patches, perhaps you can eliminate the temporary
>>>> variable and change the loop to the more common form of
>>>>
>>>> for (i = 0; i < ARRAY_SIZE(array); i++) {
>>> Thanks, I think it's better too. Here's the modified patch.
>>>
>>> A patch to use ARRAY_SIZE macro when appropriate.
>>>
>>> Signed-off-by: Ahmed S. Darwish <[email protected]>
>>> ---
>>> diff --git a/drivers/isdn/capi/capi.c b/drivers/isdn/capi/capi.c
>>> index d22c022..87fe89c 100644
>>> --- a/drivers/isdn/capi/capi.c
>>> +++ b/drivers/isdn/capi/capi.c
>>> @@ -1456,10 +1456,9 @@ static struct procfsentries {
>>>
>>> static void __init proc_init(void)
>>> {
>>> - int nelem = sizeof(procfsentries)/sizeof(procfsentries[0]);
>>> int i;
>>>
>>> - for (i=0; i < nelem; i++) {
>>> + for (i = 0; i < ARRAY_SIZE(procfsentries); i++) {
>>> struct procfsentries *p = procfsentries + i;
>>> p->procent = create_proc_entry(p->name, p->mode, NULL);
>>> if (p->procent) p->procent->read_proc = p->read_proc;
>>> @@ -1468,10 +1467,9 @@ static void __init proc_init(void)
>>>
>>> static void __exit proc_exit(void)
>>> {
>>> - int nelem = sizeof(procfsentries)/sizeof(procfsentries[0]);
>>> int i;
>>>
>>> - for (i=nelem-1; i >= 0; i--) {
>>> + for (i = ARRAY_SIZE(procfsentries) - 1; i >= 0; i--) {
>>
>> I would write such decrementing loops as :
>>
>> for (i = ARRAY_SIZE(procfsentries); --i >= 0; ) {
>>
>> Long time ago, that produced better code. I did not check recently
>> though.
>
> Why would you write "--i >= 0" instead of just "i--"? The size of an
> array can't be negative.
>
In my opinion, the first way of writing it is the way to go. I've not
seen it put like the 2nd or 3rd way anywhere in the kernel (of course I
haven't read all of the code), and while it's correct, it's less
readable. I don't think gcc would generate different code between
variant 1 and 2, and anyway, this is called once at module init/exit
time, so whether you save 10 cycles there or not is totally insignificant.
--Kai
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