[FFmpeg-devel] [PATCH 02/10] crc: add av_crc_bits() to compute CRC on block with bit boundary

[Rostislav Pehlivanov]

On 20 December 2017 at 19:58, Aurelien Jacobs <aurel at gnuage.org> wrote:

> ---
>  libavutil/crc.c | 20 ++++++++++++++++++++
>  libavutil/crc.h | 12 ++++++++++++
>  2 files changed, 32 insertions(+)
>
> diff --git a/libavutil/crc.c b/libavutil/crc.c
> index 8e44a76ec8..cb26a09a20 100644
> --- a/libavutil/crc.c
> +++ b/libavutil/crc.c
> @@ -413,3 +413,23 @@ uint32_t av_crc(const AVCRC *ctx, uint32_t crc,
>
>      return crc;
>  }
> +
> +uint32_t av_crc_bits(const AVCRC *ctx, uint32_t crc,
> +                     const uint8_t *buffer, size_t length)
> +{
> +    size_t byte_length = length >> 3;
> +    int bit_length = length & 7;
> +
> +    crc = av_crc(ctx, crc, buffer, byte_length);
> +
> +    if (bit_length) {
> +        uint8_t bits = buffer[byte_length];
> +        while (bit_length--) {
> +            int8_t mask = (bits ^ crc);
> +            crc = (crc << 1) ^ (ctx[1] & (mask >> 7));
> +            bits <<= 1;
> +        }
> +    }
> +
> +    return crc;
> +}
> diff --git a/libavutil/crc.h b/libavutil/crc.h
> index e57a1af903..bde31f858a 100644
> --- a/libavutil/crc.h
> +++ b/libavutil/crc.h
> @@ -86,6 +86,7 @@ const AVCRC *av_crc_get_table(AVCRCId crc_id);
>  /**
>   * Calculate the CRC of a block.
>   * @param crc CRC of previous blocks if any or initial value for CRC
> + * @param length number of bytes in the given block
>   * @return CRC updated with the data from the given block
>   *
>   * @see av_crc_init() "le" parameter
> @@ -93,6 +94,17 @@ const AVCRC *av_crc_get_table(AVCRCId crc_id);
>  uint32_t av_crc(const AVCRC *ctx, uint32_t crc,
>                  const uint8_t *buffer, size_t length) av_pure;
>
> +/**
> + * Calculate the CRC of a block with bits boundary.
> + * @param crc CRC of previous blocks if any or initial value for CRC
> + * @param length number of bits in the given block
> + * @return CRC updated with the data from the given block
> + *
> + * @see av_crc_init() "le" parameter
> + */
> +uint32_t av_crc_bits(const AVCRC *ctx, uint32_t crc,
> +                     const uint8_t *buffer, size_t length) av_pure;
> +
>  /**
>   * @}
>   */
> --
> 2.15.1
>
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>

Sorry, I didn't see that sbc does fucked up crc on 7 bits.
In that case could you submit a new version of just the sbc patch which
adds this back in the decoder?
If you can point out another CRC, even a non-multimedia one, which does
calculations on a non-byte aligned (but continuous, without skipping bits)
buffer I'd accept this patch though.