[FFmpeg-devel] [PATCH] Heavy optimization of IFF decoder

[Ronald S. Bultje]

Hi,

On Tue, Apr 27, 2010 at 3:05 PM, Sebastian Vater
<cdgs.basty at googlemail.com> wrote:
> M?ns Rullg?rd a ?crit :
>> Sebastian Vater <cdgs.basty at googlemail.com> writes:
>>> ?{
>>> ? ? ?GetBitContext gb;
>>> ? ? ?unsigned int i;
>>> ? ? ?const unsigned b = (buf_size * 8) + bps - 1;
>>> + ? ?const unsigned b32 = b & ~3;
>>> ? ? ?init_get_bits(&gb, buf, buf_size * 8);
>>> - ? ?for(i = 0; i < b; i++) {
>>> + ? ?for(i = 0; i < b32; i += 4) {
>>> + ? ? ? ?const uint32_t v = decodeplane8_tab[plane][get_bits(&gb, 4)];
>>> + ? ? ? ?AV_WN32A(dst+i, AV_RN32A(dst+i) | v);
>>> + ? ?}
>>>
>>
>> I suggest using a local variable here, like this:
>>
>> ? ? const uint32_t *lut = decodeplane8_tab[plane];
>> ? ? [...]
>> ? ? uint32_t v = lut[get_bits(...)];
>>
>> I don't trust gcc to do that on its own.
>>
> Didn't change anything, i.e. still 20% slower...what now?

With that, it becomes from 20% slower to 3-4% faster for me. Check
your performance again, or increase the amount of cycles in
decodeplane8() (as Mans suggested earlier in this thread).

Ronald