[FFmpeg-devel] [RFC][PATCH 1/3] lavu: Add av_crc2() and av_crc2_init()

[Michael Niedermayer]

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.*
besides the code added is buggy


[...]
> +    ctx[256] = 1;
> +#if !CONFIG_SMALL
> +    if (ctx_size >= sizeof(AVCRCX) * 1024)
> +        for (i = 0; i < 256; i++)
> +            for (j = 0; j < 3; j++)
> +                ctx[256 *(j + 1) + i] =
> +                    (ctx[256 * j + i] >> 8) ^ ctx[ctx[256 * j + i] & 0xFF];

this is wrong, 64bits are not made of 4 bytes

theres more code thats wrong in the same way

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

The misfortune of the wise is better than the prosperity of the fool.
-- Epicurus
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