On Thu, Jul 14, 2022 at 9:13 AM ChiaEn Wu [off-list ref] wrote:

Andy Shevchenko [off-list ref] 於 2022年7月13日 週三 晚上8:07寫道：

quoted

On Wed, Jul 13, 2022 at 12:53 PM ChiaEn Wu [off-list ref] wrote:

quoted

Andy Shevchenko [off-list ref] 於 2022年7月5日 週二 清晨5:14寫道：

quoted

On Mon, Jul 4, 2022 at 7:43 AM ChiaEn Wu [off-list ref] wrote:

Please, once again, remove unneeded context when replying!
^^^^^^^

...

quoted

quoted

quoted

quoted

+               prop_val = (ilog2(roundup_pow_of_two(prop_val)) + 1) >> 1;

Isn't something closer to get_order() or fls()?

I will revise it to "(get_order(prop_va * PAGE_SIZE) + 1) / 2" and
this change is meet your expectations??

Nope. Try again. What about fls()?

I have tried two methods so far, as follows
-------------------------------------------------------------
/*
 * prop_val =  1      -->  1 steps --> b'00
 * prop_val =  2 ~  4 -->  4 steps --> b'01
 * prop_val =  5 ~ 16 --> 16 steps --> b'10
 * prop_val = 17 ~ 64 --> 64 steps --> b'11
*/

So, for 1 --> 0, for 2 --> 1, for 5 --> 2, and for 17 --> 3.
Now, consider x - 1:
0  ( 0 ) --> 0
1  (2^0) --> 1
4  (2^2) --> 2
16 (2^4) --> 3
64 (2^6) --> ? (but let's consider that the range has been checked already)

Since we take the lower limit, it means ffs():

  y = (ffs(x - 1) + 1) / 2;

Does it work for you?

// 1. use fls() and ffs() combination
prop_val = ffs(prop_val) == fls(prop_val) ? fls(prop_val) >> 1 :
(fls(prop_val) + 1) >> 1;

// 2. use one line for-loop, but without fls()
for (i = --prop_val, prop_val = 0; i >> 2 * prop_val != 0; prop_val++);
-------------------------------------------------------------
Do these changes meet your expectations??

No, this is ugly. Yes, I understand that a bit arithmetics is hard...

-- 
With Best Regards,
Andy Shevchenko