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Subject: Re: [PATCH v18 05/10] xbitmap: add more operations

On 12/03/2017 09:50 AM, Tetsuo Handa wrote:
Matthew Wilcox wrote:
On Fri, Dec 01, 2017 at 03:09:08PM +0000, Wang, Wei W wrote:
On Friday, December 1, 2017 9:02 PM, Tetsuo Handa wrote:
If start == end is legal,

    for (; start < end; start = (start | (IDA_BITMAP_BITS - 1)) + 1) {

makes this loop do nothing because 10 < 10 is false.
How about "start <= end "?
Don't ask Tetsuo for his opinion, write some userspace code that uses it.

Please be sure to prepare for "end == -1UL" case, for "start < end" will become
true when "start = (start | (IDA_BITMAP_BITS - 1)) + 1" made "start == 0" due to

I think there is one more corner case with this API: searching for bit "1" from [0, ULONG_MAX] while no bit is set in the range, there appear to be no possible value that we can return (returning "end + 1" will be "ULONG_MAX + 1", which is 0) I plan to make the "end" be exclusive of the searching, that is, [start, end), and return "end" if no such bit is found.

For cases like [16, 16), returning 16 doesn't mean bit 16 is 1 or 0, it simply means there is no bits to search in the given range, since 16 is exclusive.

Please let me know if you have a different thought.


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