Re: [PATCH v5 1/8] Btrfs: introduce a tree for items that map UUIDs to something

[Stefan Behrens <sbehrens@giantdisaster.de>]

On Fri, 21 Jun 2013 09:11:38 -0700, Zach Brown wrote:
>>>> +	offset = (unsigned long)ptr;
>>>> +	while (sub_item_len > 0) {
>>>> +		u64 data;
>>>> +
>>>> +		read_extent_buffer(eb, &data, offset, sizeof(data));
>>>> +		data = le64_to_cpu(data);
>>>> +		if (data == subid) {
>>>> +			ret = 0;
>>>> +			break;
>>>> +		}
>>>> +		offset += sizeof(data);
>>>> +		sub_item_len--;
>>>> +	}
>>>
>>> This could be cleaned up a bit by comparing an on-stack little-endian
>>> input subid with each little-endian subid in the item with
>>> memcmp_extent_buffer().
>>
>> This would save some CPU cycles for the repeated le64_to_cpu() and for
>> the memcpy(). The number of lines of code is equal for both ways.
> 
> Hmm?  It would be many fewer lines of code.

Are you thinking of something shorter than the following?

offset = (unsigned long)ptr;
subid = cpu_to_le64(subid);
while (sub_item_len > 0) {
	if (memcmp_extent_buffer(eb, &subid, offset,
				 sizeof(subid)) == 0) {
		ret = 0;
		break;
	}
	offset += sizeof(subid);
	sub_item_len--;
}