[alsa-devel] [PATCH 09/39] firewire-lib: Add sort function for transmitted packet

[Takashi Sakamoto]

Iwai-san,

Thanks for your reviewing.

(Feb 28 2014 15:40), Takashi Iwai wrote:
>> +#define SWAP(tbl, m, n) \
>> +	t = tbl[n].id; \
>> +	tbl[n].id = tbl[m].id; \
>> +	tbl[m].id = t; \
>> +	t = tbl[n].dbc; \
>> +	tbl[n].dbc = tbl[m].dbc; \
>> +	tbl[m].dbc = t; \
>> +	t = tbl[n].payload_size; \
>> +	tbl[n].payload_size = tbl[m].payload_size; \
>> +	tbl[m].payload_size = t;
>
> Why swap() macro can't be used instead?

Because I didn't know the macro... I confirm it in kernel.h. Thank you.

>> +static void packet_sort(struct sort_table *tbl, unsigned int len)
>> +{
>> +	unsigned int i, j, k, t;
>> +
>> +	i = 0;
>> +	do {
>> +		for (j = i + 1; j < len; j++) {
>> +			if (((tbl[i].dbc > tbl[j].dbc) &&
>> +			     (tbl[i].dbc - tbl[j].dbc < DBC_THRESHOLD))) {
>> +				SWAP(tbl, i, j);
>> +			} else if ((tbl[j].dbc > tbl[i].dbc) &&
>> +				   (tbl[j].dbc - tbl[i].dbc >
>> +							DBC_THRESHOLD)) {
>> +				for (k = i; k > 0; k--) {
>> +					if ((tbl[k].dbc > tbl[j].dbc) ||
>> +					    (tbl[j].dbc - tbl[k].dbc >
>> +							DBC_THRESHOLD)) {
>> +						SWAP(tbl, j, k);
>> +					}
>> +					break;
>> +				}
>> +			}
>> +			break;
>> +		}
>> +		i = j;
>> +	} while (i < len);
>> +}
>
> You can use the standard sort() function (available in linux/sort.h).

According to /lib/sort.c, it's for heap sort.

Currently I think I cannot write this algorism as heap sort because data 
consist of cyclic numbers, A simple example is:
[4, 5, 0, 2, 1, 3, 4, 0, 5, 1, 3, 2, 4, 0, 1, 5]
After sorting, this sequence of number should be:
[4, 5, 0, 1, 2, 3, 4, 5, 0, 1, 2, 3, 4, 5, 0, 1]

And we need to use stable sort algorism because there are successive 
elements with the same value.

If you want to see actual example, please see [PATCH 21/39]. A sequence 
of the last four bytes in 'CIP header 1' is data to be sort.

>> +	/* for sorting transmitted packets */
>> +	if (s->direction == AMDTP_IN_STREAM) {
>> +		s->remain_packets = 0;
>> +		s->sort_table = kzalloc(sizeof(struct sort_table) *
>> +					QUEUE_LENGTH, GFP_KERNEL);
>> +		if (s->sort_table == NULL)
>> +			return -ENOMEM;
>> +		s->left_packets = kzalloc(amdtp_stream_get_max_payload(s) *
>> +					  QUEUE_LENGTH / 4, GFP_KERNEL);
>
> NULL check missing?

OK. I forgot it.


Thanks

Takashi Sakamoto
o-takashi at sakamocchi.jp