[FFmpeg-devel] [RFC][PATCH 1/3] lavu: Add av_crc2() and av_crc2_init()
michaelni at gmx.at
Tue Jan 29 01:04:21 CET 2013
On Mon, Jan 28, 2013 at 07:29:36PM -0300, James Almer wrote:
> On 28/01/13 11:38 AM, Michael Niedermayer wrote:
> > On Mon, Jan 28, 2013 at 04:31:53AM -0300, James Almer wrote:
> >> Functionally the same as av_crc() and av_crc_init(), but
> >> supporting CRCs of up to 64 bits.
> >> Signed-off-by: James Almer <jamrial at gmail.com>
> >> ---
> >> libavutil/crc.c | 75 ++++++++++++------------------------------
> >> libavutil/crc.h | 7 ++++
> >> libavutil/crc_template.c | 85 ++++++++++++++++++++++++++++++++++++++++++++++++
> >> 3 files changed, 112 insertions(+), 55 deletions(-)
> >> create mode 100644 libavutil/crc_template.c
> > thats a huge mess for calculating a crc once for a few bytes of a
> > tta password.
> > something like:
> > for all bytes
> > c ^= (uint64_t)*byte++ << 56;
> > for(i=0; i<8; i++)
> > c = (c << 1) ^ (poly & (((int64_t) c) >> 63));
> > in tta will do the samem, saving all the hundreads of lines of code
> > added to crc.*
> I started that way, adding the calculation in tta, but then figured i might as
> well just add support for CRCs of more than 32 bits to libavutil in case something
> else needs them in the future.
> I'll send a patch later today to get the calculation done within tta.
i wouldnt mind it in libavutil if there was need for it (some speed
relevant code using it) but ATM its quite a lot macro/template mess
to avoid significantly fewer lines in tta*
so yes i think ATM its better in tta
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
Old school: Use the lowest level language in which you can solve the problem
New school: Use the highest level language in which the latest supercomputer
can solve the problem without the user falling asleep waiting.
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