[FFmpeg-devel] [PATCH] avcodec: add Apple Pixlet decoder

[James Almer]

On 12/19/2016 11:18 AM, Paul B Mahol wrote:
> +static int read_low_coeffs(AVCodecContext *avctx, int16_t *dst, int size)
> +{
> +    PixletContext *ctx = avctx->priv_data;
> +    GetBitContext *b = &ctx->gbit;
> +    unsigned value, cnt1, nbits, j, i = 0;
> +    int rlen, flag = 0, escape;
> +    int64_t rparam = 3;
> +
> +    while (i < size) {
> +        nbits = FFMIN(ff_clz((rparam >> 8) + 3) ^ 0x1F, 14);
> +
> +        cnt1 = get_unary(b, 0, 8);
> +        if (cnt1 < 8) {
> +            value = show_bits(b, nbits);
> +            if (value <= 1) {
> +                skip_bits(b, nbits - 1);
> +                escape = ((1 << nbits) - 1) * cnt1;
> +            } else {
> +                skip_bits(b, nbits);
> +                escape = value + ((1 << nbits) - 1) * cnt1 - 1;
> +            }
> +        } else {
> +            escape = get_bits(b, 16);
> +        }
> +
> +        rlen = -((escape + flag) & 1) | 1;
> +        dst[i++] = rlen * ((escape + flag + 1) >> 1);
> +        rparam += 120 * (escape + flag) - (120 * rparam >> 8);
> +        flag = 0;
> +
> +        if (rparam * 4 > 0xFF || i >= size)
> +            continue;
> +
> +        nbits = ((rparam + 8) >> 5) + (rparam ? ff_clz(rparam) : 32) - 24;
> +        escape = 16383 & ((1 << nbits) - 1);

escape = av_mod_uintp2(16383, nbits);

> +        cnt1 = get_unary(b, 0, 8);
> +        if (cnt1 > 7) {
> +            rlen = get_bits(b, 16);
> +        } else {
> +            value = show_bits(b, nbits);
> +            if (value > 1) {
> +                skip_bits(b, nbits);
> +                rlen = value + escape * cnt1 - 1;
> +            } else {
> +                if (nbits - 1 > 0)
> +                    skip_bits(b, nbits - 1);
> +                rlen = escape * cnt1;
> +            }
> +        }
> +
> +        if (i + rlen > size)
> +            return AVERROR_INVALIDDATA;
> +
> +        for (j = 0; j < rlen; j++)
> +            dst[i++] = 0;
> +
> +        rparam = 0;
> +        flag = rlen < 0xFFFF ? 1 : 0;
> +    }
> +
> +    align_get_bits(b);
> +    return get_bits_count(b) >> 3;
> +}