Re: [FFmpeg-devel] [PATCH 1/3] avcodec/hcadec: Don't use GetBit-API for byte-aligned reads

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

Andreas Rheinhardt:
> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
> ---
>  libavcodec/hcadec.c | 80 ++++++++++++++++++++++-----------------------
>  1 file changed, 39 insertions(+), 41 deletions(-)
> 
> diff --git a/libavcodec/hcadec.c b/libavcodec/hcadec.c
> index 4e84942bb9..73ff62139d 100644
> --- a/libavcodec/hcadec.c
> +++ b/libavcodec/hcadec.c
> @@ -23,6 +23,7 @@
>  #include "libavutil/tx.h"
>  
>  #include "avcodec.h"
> +#include "bytestream.h"
>  #include "codec_internal.h"
>  #include "get_bits.h"
>  #include "internal.h"
> @@ -106,7 +107,7 @@ static inline unsigned ceil2(unsigned a, unsigned b)
>  static av_cold int decode_init(AVCodecContext *avctx)
>  {
>      HCAContext *c = avctx->priv_data;
> -    GetBitContext *gb = &c->gb;
> +    GetByteContext gb0, *const gb = &gb0;
>      int8_t r[16] = { 0 };
>      float scale = 1.f / 8.f;
>      unsigned b, chunk;
> @@ -118,41 +119,42 @@ static av_cold int decode_init(AVCodecContext *avctx)
>      if (avctx->ch_layout.nb_channels <= 0 || avctx->ch_layout.nb_channels > 16)
>          return AVERROR(EINVAL);
>  
> -    ret = init_get_bits8(gb, avctx->extradata, avctx->extradata_size);
> -    if (ret < 0)
> -        return ret;
> -    skip_bits_long(gb, 32);
> -    version = get_bits(gb, 16);
> -    skip_bits_long(gb, 16);
> +    if (avctx->extradata_size < 36)
> +        return AVERROR_INVALIDDATA;
> +    bytestream2_init(gb, avctx->extradata, avctx->extradata_size);
> +
> +    bytestream2_skipu(gb, 4);
> +    version = bytestream2_get_be16(gb);
> +    bytestream2_skipu(gb, 2);
>  
>      c->ath_type = version >= 0x200 ? 0 : 1;
>  
> -    if (get_bits_long(gb, 32) != MKBETAG('f', 'm', 't', 0))
> +    if (bytestream2_get_be32u(gb) != MKBETAG('f', 'm', 't', 0))
>          return AVERROR_INVALIDDATA;
> -    skip_bits_long(gb, 32);
> -    skip_bits_long(gb, 32);
> -    skip_bits_long(gb, 32);
> +    bytestream2_skipu(gb, 4);
> +    bytestream2_skipu(gb, 4);
> +    bytestream2_skipu(gb, 4);
>  
> -    chunk = get_bits_long(gb, 32);
> +    chunk = bytestream2_get_be32u(gb);
>      if (chunk == MKBETAG('c', 'o', 'm', 'p')) {
> -        skip_bits_long(gb, 16);
> -        skip_bits_long(gb, 8);
> -        skip_bits_long(gb, 8);
> -        c->track_count = get_bits(gb, 8);
> -        c->channel_config = get_bits(gb, 8);
> -        c->total_band_count = get_bits(gb, 8);
> -        c->base_band_count = get_bits(gb, 8);
> -        c->stereo_band_count = get_bits(gb, 8);
> -        c->bands_per_hfr_group = get_bits(gb, 8);
> +        bytestream2_skipu(gb, 2);
> +        bytestream2_skipu(gb, 1);
> +        bytestream2_skipu(gb, 1);
> +        c->track_count         = bytestream2_get_byteu(gb);
> +        c->channel_config      = bytestream2_get_byteu(gb);
> +        c->total_band_count    = bytestream2_get_byteu(gb);
> +        c->base_band_count     = bytestream2_get_byteu(gb);
> +        c->stereo_band_count   = bytestream2_get_byte (gb);
> +        c->bands_per_hfr_group = bytestream2_get_byte (gb);
>      } else if (chunk == MKBETAG('d', 'e', 'c', 0)) {
> -        skip_bits_long(gb, 16);
> -        skip_bits_long(gb, 8);
> -        skip_bits_long(gb, 8);
> -        c->total_band_count = get_bits(gb, 8) + 1;
> -        c->base_band_count = get_bits(gb, 8) + 1;
> -        c->track_count = get_bits(gb, 4);
> -        c->channel_config = get_bits(gb, 4);
> -        if (!get_bits(gb, 8))
> +        bytestream2_skipu(gb, 2);
> +        bytestream2_skipu(gb, 1);
> +        bytestream2_skipu(gb, 1);
> +        c->total_band_count = bytestream2_get_byteu(gb) + 1;
> +        c->base_band_count  = bytestream2_get_byteu(gb) + 1;
> +        c->track_count      = bytestream2_peek_byteu(gb) >> 4;
> +        c->channel_config   = bytestream2_get_byteu(gb) & 0xF;
> +        if (!bytestream2_get_byteu(gb))
>              c->base_band_count = c->total_band_count;
>          c->stereo_band_count = c->total_band_count - c->base_band_count;
>          c->bands_per_hfr_group = 0;
> @@ -163,24 +165,20 @@ static av_cold int decode_init(AVCodecContext *avctx)
>          return AVERROR_INVALIDDATA;
>  
>  
> -    while (get_bits_left(gb) >= 32) {
> -        chunk = get_bits_long(gb, 32);
> +    while (bytestream2_get_bytes_left(gb) >= 4) {
> +        chunk = bytestream2_get_be32u(gb);
>          if (chunk == MKBETAG('v', 'b', 'r', 0)) {
> -            skip_bits_long(gb, 16);
> -            skip_bits_long(gb, 16);
> +            bytestream2_skip(gb, 2 + 2);
>          } else if (chunk == MKBETAG('a', 't', 'h', 0)) {
> -            c->ath_type = get_bits(gb, 16);
> +            c->ath_type = bytestream2_get_be16(gb);
>          } else if (chunk == MKBETAG('r', 'v', 'a', 0)) {
> -            skip_bits_long(gb, 32);
> +            bytestream2_skip(gb, 4);
>          } else if (chunk == MKBETAG('c', 'o', 'm', 'm')) {
> -            skip_bits_long(gb, get_bits(gb, 8) * 8);
> +            bytestream2_skip(gb, bytestream2_get_byte(gb) * 8);
>          } else if (chunk == MKBETAG('c', 'i', 'p', 'h')) {
> -            skip_bits_long(gb, 16);
> +            bytestream2_skip(gb, 2);
>          } else if (chunk == MKBETAG('l', 'o', 'o', 'p')) {
> -            skip_bits_long(gb, 32);
> -            skip_bits_long(gb, 32);
> -            skip_bits_long(gb, 16);
> -            skip_bits_long(gb, 16);
> +            bytestream2_skip(gb, 4 + 4 + 2 + 2);
>          } else if (chunk == MKBETAG('p', 'a', 'd', 0)) {
>              break;
>          } else {

Will apply this patchset later today unless there are objections.

- Andreas
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