[FFmpeg-devel] [PATCH 06/25] avcodec/magicyuv: Don't use GetBit API for byte-aligned reads

[Paul B Mahol]

On Sat, Sep 26, 2020 at 12:27:45PM +0200, Andreas Rheinhardt wrote:
> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at gmail.com>
> ---
>  libavcodec/magicyuv.c | 45 +++++++++++++++++++++----------------------
>  1 file changed, 22 insertions(+), 23 deletions(-)

lgtm

> 
> diff --git a/libavcodec/magicyuv.c b/libavcodec/magicyuv.c
> index 6c29efc9f4..f7dfef0eb8 100644
> --- a/libavcodec/magicyuv.c
> +++ b/libavcodec/magicyuv.c
> @@ -270,27 +270,26 @@ static int magy_decode_slice(AVCodecContext *avctx, void *tdata,
>          int sheight = AV_CEIL_RSHIFT(s->slice_height, s->vshift[i]);
>          ptrdiff_t fake_stride = p->linesize[i] * (1 + interlaced);
>          ptrdiff_t stride = p->linesize[i];
> +        const uint8_t *slice = s->buf + s->slices[i][j].start;
>          int flags, pred;
> -        int ret = init_get_bits8(&gb, s->buf + s->slices[i][j].start,
> -                                 s->slices[i][j].size);
> -
> -        if (ret < 0)
> -            return ret;
>  
> -        flags = get_bits(&gb, 8);
> -        pred  = get_bits(&gb, 8);
> +        flags = bytestream_get_byte(&slice);
> +        pred  = bytestream_get_byte(&slice);
>  
>          dst = p->data[i] + j * sheight * stride;
>          if (flags & 1) {
> -            if (get_bits_left(&gb) < 8* width * height)
> +            if (s->slices[i][j].size - 2 < width * height)
>                  return AVERROR_INVALIDDATA;
>              for (k = 0; k < height; k++) {
> -                for (x = 0; x < width; x++)
> -                    dst[x] = get_bits(&gb, 8);
> -
> +                bytestream_get_buffer(&slice, dst, width);
>                  dst += stride;
>              }
>          } else {
> +            int ret = init_get_bits8(&gb, slice, s->slices[i][j].size - 2);
> +
> +            if (ret < 0)
> +                return ret;
> +
>              for (k = 0; k < height; k++) {
>                  for (x = 0; x < width; x++) {
>                      int pix;
> @@ -385,21 +384,25 @@ static int magy_decode_slice(AVCodecContext *avctx, void *tdata,
>      return 0;
>  }
>  
> -static int build_huffman(AVCodecContext *avctx, GetBitContext *gbit, int max)
> +static int build_huffman(AVCodecContext *avctx, const uint8_t *table,
> +                         int table_size, int max)
>  {
>      MagicYUVContext *s = avctx->priv_data;
> +    GetByteContext gb;
>      HuffEntry he[4096];
>      int i = 0, j = 0, k;
>  
> -    while (get_bits_left(gbit) >= 8) {
> -        int b = get_bits(gbit, 1);
> -        int x = get_bits(gbit, 7);
> +    bytestream2_init(&gb, table, table_size);
> +
> +    while (bytestream2_get_bytes_left(&gb) > 0) {
> +        int b = bytestream2_peek_byteu(&gb) &  0x80;
> +        int x = bytestream2_get_byteu(&gb)  & ~0x80;
>          int l = 1;
>  
>          if (b) {
> -            if (get_bits_left(gbit) < 8)
> +            if (bytestream2_get_bytes_left(&gb) <= 0)
>                  break;
> -            l += get_bits(gbit, 8);
> +            l += bytestream2_get_byteu(&gb);
>          }
>          k = j + l;
>          if (k > max || x == 0 || x > 32) {
> @@ -440,7 +443,6 @@ static int magy_decode_frame(AVCodecContext *avctx, void *data,
>      ThreadFrame frame = { .f = data };
>      AVFrame *p = data;
>      GetByteContext gbyte;
> -    GetBitContext gbit;
>      uint32_t first_offset, offset, next_offset, header_size, slice_width;
>      int width, height, format, version, table_size;
>      int ret, i, j;
> @@ -632,11 +634,8 @@ static int magy_decode_frame(AVCodecContext *avctx, void *data,
>      if (table_size < 2)
>          return AVERROR_INVALIDDATA;
>  
> -    ret = init_get_bits8(&gbit, avpkt->data + bytestream2_tell(&gbyte), table_size);
> -    if (ret < 0)
> -        return ret;
> -
> -    ret = build_huffman(avctx, &gbit, s->max);
> +    ret = build_huffman(avctx, avpkt->data + bytestream2_tell(&gbyte),
> +                        table_size, s->max);
>      if (ret < 0)
>          return ret;
>  
> -- 
> 2.25.1
> 
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