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From: | Wei Wang |
Subject: | Re: [Qemu-devel] [PATCH v18 05/10] xbitmap: add more operations |
Date: | Thu, 07 Dec 2017 20:01:24 +0800 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 |
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 overflow.
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. Best, Wei
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