gst-nvvideo4linux2/gst-v4l2/nalutils.c

/*
 * Copyright (c) 2023, NVIDIA CORPORATION. All rights reserved.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with this library; if not, write to the
 * Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
 * Boston, MA 02110-1301, USA.
 *
 */

#ifdef HAVE_CONFIG_H
#  include "config.h"
#endif

#include "nalutils.h"

/* Compute Ceil(Log2(v)) */
/* Derived from branchless code for integer log2(v) from:
   <http://graphics.stanford.edu/~seander/bithacks.html#IntegerLog> */
guint
ceil_log2 (guint32 v)
{
  guint r, shift;

  v--;
  r = (v > 0xFFFF) << 4;
  v >>= r;
  shift = (v > 0xFF) << 3;
  v >>= shift;
  r |= shift;
  shift = (v > 0xF) << 2;
  v >>= shift;
  r |= shift;
  shift = (v > 0x3) << 1;
  v >>= shift;
  r |= shift;
  r |= (v >> 1);
  return r + 1;
}

/****** Nal parser ******/

void
init_nal (NalReader * nr, const guint8 * data, guint size)
{
  nr->data = data;
  nr->size = size;
  nr->n_epb = 0;

  nr->byte = 0;
  nr->bits_in_cache = 0;
  /* fill with something other than 0 to detect emulation prevention bytes */
  nr->first_byte = 0xff;
  nr->cache = 0xff;
}

gboolean
_read (NalReader * nr, guint nbits)
{
  if (G_UNLIKELY (nr->byte * 8 + (nbits - nr->bits_in_cache) > nr->size * 8)) {
    GST_DEBUG ("Can not read %u bits, bits in cache %u, Byte * 8 %u, size in "
        "bits %u", nbits, nr->bits_in_cache, nr->byte * 8, nr->size * 8);
    return FALSE;
  }

  while (nr->bits_in_cache < nbits) {
    guint8 byte;
    gboolean check_three_byte;

    check_three_byte = TRUE;
  next_byte:
    if (G_UNLIKELY (nr->byte >= nr->size))
      return FALSE;

    byte = nr->data[nr->byte++];

    /* check if the byte is a emulation_prevention_three_byte */
    if (check_three_byte && byte == 0x03 && nr->first_byte == 0x00 &&
        ((nr->cache & 0xff) == 0)) {
      /* next byte goes unconditionally to the cache, even if it's 0x03 */
      check_three_byte = FALSE;
      nr->n_epb++;
      goto next_byte;
    }
    nr->cache = (nr->cache << 8) | nr->first_byte;
    nr->first_byte = byte;
    nr->bits_in_cache += 8;
  }

  return TRUE;
}

/* Skips the specified amount of bits. This is only suitable to a
   cacheable number of bits */
gboolean
_skip (NalReader * nr, guint nbits)
{
  g_assert (nbits <= 8 * sizeof (nr->cache));

  if (G_UNLIKELY (!_read (nr, nbits)))
    return FALSE;

  nr->bits_in_cache -= nbits;

  return TRUE;
}

/* Generic version to skip any number of bits */
gboolean
_skip_long (NalReader * nr, guint nbits)
{
  /* Leave out enough bits in the cache once we are finished */
  const guint skip_size = 4 * sizeof (nr->cache);
  guint remaining = nbits;

  nbits %= skip_size;
  while (remaining > 0) {
    if (!_skip (nr, nbits))
      return FALSE;
    remaining -= nbits;
    nbits = skip_size;
  }
  return TRUE;
}

guint
_get_pos (const NalReader * nr)
{
  return nr->byte * 8 - nr->bits_in_cache;
}

guint
_get_remaining (const NalReader * nr)
{
  return (nr->size - nr->byte) * 8 + nr->bits_in_cache;
}

guint
_get_epb_count (const NalReader * nr)
{
  return nr->n_epb;
}

#define _READ_BITS(bits) \
gboolean \
_get_bits_uint##bits (NalReader *nr, guint##bits *val, guint nbits) \
{ \
  guint shift; \
  \
  if (!_read (nr, nbits)) \
    return FALSE; \
  \
  /* bring the required bits down and truncate */ \
  shift = nr->bits_in_cache - nbits; \
  *val = nr->first_byte >> shift; \
  \
  *val |= nr->cache << (8 - shift); \
  /* mask out required bits */ \
  if (nbits < bits) \
    *val &= ((guint##bits)1 << nbits) - 1; \
  \
  nr->bits_in_cache = shift; \
  \
  return TRUE; \
} \

_READ_BITS (8);
_READ_BITS (16);
_READ_BITS (32);

#define _PEEK_BITS(bits) \
gboolean \
_peek_bits_uint##bits (const NalReader *nr, guint##bits *val, guint nbits) \
{ \
  NalReader tmp; \
  \
  tmp = *nr; \
  return _get_bits_uint##bits (&tmp, val, nbits); \
}

_PEEK_BITS (8);

gboolean
_get_ue (NalReader * nr, guint32 * val)
{
  guint i = 0;
  guint8 bit;
  guint32 value;

  if (G_UNLIKELY (!_get_bits_uint8 (nr, &bit, 1)))
    return FALSE;

  while (bit == 0) {
    i++;
    if (G_UNLIKELY (!_get_bits_uint8 (nr, &bit, 1)))
      return FALSE;
  }

  if (G_UNLIKELY (i > 31))
    return FALSE;

  if (G_UNLIKELY (!_get_bits_uint32 (nr, &value, i)))
    return FALSE;

  *val = (1 << i) - 1 + value;

  return TRUE;
}

gboolean
_get_se (NalReader * nr, gint32 * val)
{
  guint32 value;

  if (G_UNLIKELY (!_get_ue (nr, &value)))
    return FALSE;

  if (value % 2)
    *val = (value / 2) + 1;
  else
    *val = -(value / 2);

  return TRUE;
}

gboolean
_is_byte_aligned (NalReader * nr)
{
  if (nr->bits_in_cache != 0)
    return FALSE;
  return TRUE;
}

gboolean
_has_more_data (NalReader * nr)
{
  NalReader nr_tmp;
  guint remaining, nbits;
  guint8 rbsp_stop_one_bit, zero_bits;

  remaining = _get_remaining (nr);
  if (remaining == 0)
    return FALSE;

  nr_tmp = *nr;
  nr = &nr_tmp;

  /* The spec defines that more_rbsp_data() searches for the last bit
     equal to 1, and that it is the rbsp_stop_one_bit. Subsequent bits
     until byte boundary is reached shall be zero.

     This means that more_rbsp_data() is FALSE if the next bit is 1
     and the remaining bits until byte boundary are zero. One way to
     be sure that this bit was the very last one, is that every other
     bit after we reached byte boundary are also set to zero.
     Otherwise, if the next bit is 0 or if there are non-zero bits
     afterwards, then then we have more_rbsp_data() */
  if (!_get_bits_uint8 (nr, &rbsp_stop_one_bit, 1))
    return FALSE;
  if (!rbsp_stop_one_bit)
    return TRUE;

  nbits = --remaining % 8;
  while (remaining > 0) {
    if (!_get_bits_uint8 (nr, &zero_bits, nbits))
      return FALSE;
    if (zero_bits != 0)
      return TRUE;
    remaining -= nbits;
    nbits = 8;
  }
  return FALSE;
}

/***********  end of nal parser ***************/

gint
scan_for_start_codes (const guint8 * data, guint size)
{
  GstByteReader br;
  gst_byte_reader_init (&br, data, size);

  /* NALU not empty, so we can at least expect 1 (even 2) bytes following sc */
  return gst_byte_reader_masked_scan_uint32 (&br, 0xffffff00, 0x00000100,
      0, size);
}