Re: [Qemu-devel] [PATCH 2/2] migration/xbzrle: make xbzrle_encode_buffer little easier to read

[Wei Yang <richardw.yang@linux.intel.com>]

On Tue, Jun 11, 2019 at 06:59:26PM +0100, Dr. David Alan Gilbert wrote:
>* Wei Yang (richardw.yang@linux.intel.com) wrote:
>> The encoding process could be described below:
>> 
>>     for [content]
>>         get length of a run
>>         encode this run
>> 
>> By refactoring the code with this logic, it maybe a little easier to
>> understand.
>> 
>> Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
>> ---
>>  migration/xbzrle.c | 153 +++++++++++++++++++++------------------------
>>  1 file changed, 73 insertions(+), 80 deletions(-)
>> 
>> diff --git a/migration/xbzrle.c b/migration/xbzrle.c
>> index 1ba482ded9..25c69708ec 100644
>> --- a/migration/xbzrle.c
>> +++ b/migration/xbzrle.c
>> @@ -14,6 +14,59 @@
>>  #include "qemu/cutils.h"
>>  #include "xbzrle.h"
>>  
>> +static int next_run(uint8_t *old_buf, uint8_t *new_buf, int off, int slen,
>> +                    bool zrun)
>> +{
>> +    uint32_t len = 0;
>> +    long res;
>> +
>> +    res = (slen - off) % sizeof(long);
>> +
>> +    /* first unaligned bytes */
>> +    while (res) {
>> +        uint8_t xor = old_buf[off + len] ^ new_buf[off + len];
>> +
>> +        if (!(zrun ^ !!xor)) {
>> +            break;
>> +        }
>> +        len++;
>> +        res--;
>> +    }
>> +
>> +    if (res) {
>> +        return len;
>> +    }
>> +
>> +    /* word at a time for speed, use of 32-bit long okay */
>> +    while (off + len < slen) {
>> +        /* truncation to 32-bit long okay */
>> +        unsigned long mask = (unsigned long)0x0101010101010101ULL;
>> +        long xor = (*(long *)(old_buf + off + len)) ^
>> +                   (*(long *)(new_buf + off + len));
>> +
>> +        if (zrun && !(zrun ^ !!xor)) {
>
>Are lines like this really making it easier to read?
>

BTW, this line could be simplified to 

        if (!(zrun ^ !!xor)) {

>Juan: Opinion?
>
>Dave
>

-- 
Wei Yang
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