text: /*****************************************************************************
   * rdo.c: rate-distortion optimization
   *****************************************************************************
   * Copyright (C) 2005-2017 x264 project
   *
   * Authors: Loren Merritt <lorenm@u.washington.edu>
   *          Fiona Glaser <fiona@x264.com>
   *
   * This program is free software; you can redistribute it and/or modify
   * it under the terms of the GNU General Public License as published by
   * the Free Software Foundation; either version 2 of the License, or
   * (at your option) any later version.
   *
   * This program 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 General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with this program; if not, write to the Free Software
   * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02111, USA.
   *
   * This program is also available under a commercial proprietary license.
   * For more information, contact us at licensing@x264.com.
   *****************************************************************************/
  
  /* duplicate all the writer functions, just calculating bit cost
   * instead of writing the bitstream.
   * TODO: use these for fast 1st pass too. */
  
  #define RDO_SKIP_BS 1
  
  /* Transition and size tables for abs<9 MVD and residual coding */
  /* Consist of i_prefix-2 1s, one zero, and a bypass sign bit */
  uint8_t x264_cabac_transition_unary[15][128];
  uint16_t x264_cabac_size_unary[15][128];
  /* Transition and size tables for abs>9 MVD */
  /* Consist of 5 1s and a bypass sign bit */
  static uint8_t cabac_transition_5ones[128];
  static uint16_t cabac_size_5ones[128];
  
  /* CAVLC: produces exactly the same bit count as a normal encode */
  /* this probably still leaves some unnecessary computations */
  #define bs_write1(s,v)     ((s)->i_bits_encoded += 1)
  #define bs_write(s,n,v)    ((s)->i_bits_encoded += (n))
  #define bs_write_ue(s,v)   ((s)->i_bits_encoded += bs_size_ue(v))
  #define bs_write_se(s,v)   ((s)->i_bits_encoded += bs_size_se(v))
  #define bs_write_te(s,v,l) ((s)->i_bits_encoded += bs_size_te(v,l))
  #define x264_macroblock_write_cavlc  static x264_macroblock_size_cavlc
  #include "cavlc.c"
  
  /* CABAC: not exactly the same. x264_cabac_size_decision() keeps track of
   * fractional bits, but only finite precision. */
  #undef  x264_cabac_encode_decision
  #undef  x264_cabac_encode_decision_noup
  #undef  x264_cabac_encode_bypass
  #undef  x264_cabac_encode_terminal
  #define x264_cabac_encode_decision(c,x,v) x264_cabac_size_decision(c,x,v)
  #define x264_cabac_encode_decision_noup(c,x,v) x264_cabac_size_decision_noup(c,x,v)
  #define x264_cabac_encode_terminal(c)     ((c)->f8_bits_encoded += 7)
  #define x264_cabac_encode_bypass(c,v)     ((c)->f8_bits_encoded += 256)
  #define x264_cabac_encode_ue_bypass(c,e,v) ((c)->f8_bits_encoded += (bs_size_ue_big(v+(1<<e)-1)-e)<<8)
  #define x264_macroblock_write_cabac  static x264_macroblock_size_cabac
  #include "cabac.c"
  
  #define COPY_CABAC h->mc.memcpy_aligned( &cabac_tmp.f8_bits_encoded, &h->cabac.f8_bits_encoded, \
          sizeof(x264_cabac_t) - offsetof(x264_cabac_t,f8_bits_encoded) - (CHROMA444 ? 0 : (1024+12)-460) )
  #define COPY_CABAC_PART( pos, size )\
          memcpy( &cb->state[pos], &h->cabac.state[pos], size )
  
  static ALWAYS_INLINE uint64_t cached_hadamard( x264_t *h, int size, int x, int y )
  {
      static const uint8_t hadamard_shift_x[4] = {4,   4,   3,   3};
      static const uint8_t hadamard_shift_y[4] = {4-0, 3-0, 4-1, 3-1};
      static const uint8_t  hadamard_offset[4] = {0,   1,   3,   5};
      int cache_index = (x >> hadamard_shift_x[size]) + (y >> hadamard_shift_y[size])
                      + hadamard_offset[size];
      uint64_t res = h->mb.pic.fenc_hadamard_cache[cache_index];
      if( res )
          return res - 1;
      else
      {
          pixel *fenc = h->mb.pic.p_fenc[0] + x + y*FENC_STRIDE;
          res = h->pixf.hadamard_ac[size]( fenc, FENC_STRIDE );
          h->mb.pic.fenc_hadamard_cache[cache_index] = res + 1;
          return res;
      }
  }
  
  static ALWAYS_INLINE int cached_satd( x264_t *h, int size, int x, int y )
  {
      static const uint8_t satd_shift_x[3] = {3,   2,   2};
      static const uint8_t satd_shift_y[3] = {2-1, 3-2, 2-2};
      static const uint8_t  satd_offset[3] = {0,   8,   16};
      ALIGNED_16( static pixel zero[16] ) = {0};
      int cache_index = (x >> satd_shift_x[size - PIXEL_8x4]) + (y >> satd_shift_y[size - PIXEL_8x4])
                      + satd_offset[size - PIXEL_8x4];
      int res = h->mb.pic.fenc_satd_cache[cache_index];
      if( res )
          return res - 1;
      else
      {
          pixel *fenc = h->mb.pic.p_fenc[0] + x + y*FENC_STRIDE;
          int dc = h->pixf.sad[size]( fenc, FENC_STRIDE, zero, 0 ) >> 1;
          res = h->pixf.satd[size]( fenc, FENC_STRIDE, zero, 0 ) - dc;
          h->mb.pic.fenc_satd_cache[cache_index] = res + 1;
          return res;
      }
  }
  
  /* Psy RD distortion metric: SSD plus "Absolute Difference of Complexities" */
  /* SATD and SA8D are used to measure block complexity. */
  /* The difference between SATD and SA8D scores are both used to avoid bias from the DCT size.  Using SATD */
  /* only, for example, results in overusage of 8x8dct, while the opposite occurs when using SA8D. */
  
  /* FIXME:  Is there a better metric than averaged SATD/SA8D difference for complexity difference? */
  /* Hadamard transform is recursive, so a SATD+SA8D can be done faster by taking advantage of this fact. */
  /* This optimization can also be used in non-RD transform decision. */
  
  static inline int ssd_plane( x264_t *h, int size, int p, int x, int y )
  {
      ALIGNED_16( static pixel zero[16] ) = {0};
      int satd = 0;
      pixel *fdec = h->mb.pic.p_fdec[p] + x + y*FDEC_STRIDE;
      pixel *fenc = h->mb.pic.p_fenc[p] + x + y*FENC_STRIDE;
      if( p == 0 && h->mb.i_psy_rd )
      {
          /* If the plane is smaller than 8x8, we can't do an SA8D; this probably isn't a big problem. */
          if( size <= PIXEL_8x8 )
          {
              uint64_t fdec_acs = h->pixf.hadamard_ac[size]( fdec, FDEC_STRIDE );
              uint64_t fenc_acs = cached_hadamard( h, size, x, y );
              satd = abs((int32_t)fdec_acs - (int32_t)fenc_acs)
                   + abs((int32_t)(fdec_acs>>32) - (int32_t)(fenc_acs>>32));
              satd >>= 1;
          }
          else
          {
              int dc = h->pixf.sad[size]( fdec, FDEC_STRIDE, zero, 0 ) >> 1;
              satd = abs(h->pixf.satd[size]( fdec, FDEC_STRIDE, zero, 0 ) - dc - cached_satd( h, size, x, y ));
          }
          satd = (satd * h->mb.i_psy_rd * h->mb.i_psy_rd_lambda + 128) >> 8;
      }
      return h->pixf.ssd[size](fenc, FENC_STRIDE, fdec, FDEC_STRIDE) + satd;
  }
  
  static inline int ssd_mb( x264_t *h )
  {
      int chroma_size = h->luma2chroma_pixel[PIXEL_16x16];
      int chroma_ssd = ssd_plane(h, chroma_size, 1, 0, 0) + ssd_plane(h, chroma_size, 2, 0, 0);
      chroma_ssd = ((uint64_t)chroma_ssd * h->mb.i_chroma_lambda2_offset + 128) >> 8;
      return ssd_plane(h, PIXEL_16x16, 0, 0, 0) + chroma_ssd;
  }
  
  static int x264_rd_cost_mb( x264_t *h, int i_lambda2 )
  {
      int b_transform_bak = h->mb.b_transform_8x8;
      int i_ssd;
      int i_bits;
      int type_bak = h->mb.i_type;
  
      x264_macroblock_encode( h );
  
      if( h->mb.b_deblock_rdo )
          x264_macroblock_deblock( h );
  
      i_ssd = ssd_mb( h );
  
      if( IS_SKIP( h->mb.i_type ) )
      {
          i_bits = (1 * i_lambda2 + 128) >> 8;
      }
      else if( h->param.b_cabac )
      {
          x264_cabac_t cabac_tmp;
          COPY_CABAC;
          x264_macroblock_size_cabac( h, &cabac_tmp );
          i_bits = ( (uint64_t)cabac_tmp.f8_bits_encoded * i_lambda2 + 32768 ) >> 16;
      }
      else
      {
          x264_macroblock_size_cavlc( h );
          i_bits = ( (uint64_t)h->out.bs.i_bits_encoded * i_lambda2 + 128 ) >> 8;
      }
  
      h->mb.b_transform_8x8 = b_transform_bak;
      h->mb.i_type = type_bak;
  
      return X264_MIN( i_ssd + i_bits, COST_MAX );
  }
  
  /* partition RD functions use 8 bits more precision to avoid large rounding errors at low QPs */
  
  static uint64_t x264_rd_cost_subpart( x264_t *h, int i_lambda2, int i4, int i_pixel )
  {
      uint64_t i_ssd, i_bits;
  
      x264_macroblock_encode_p4x4( h, i4 );
      if( i_pixel == PIXEL_8x4 )
          x264_macroblock_encode_p4x4( h, i4+1 );
      if( i_pixel == PIXEL_4x8 )
          x264_macroblock_encode_p4x4( h, i4+2 );
  
      i_ssd = ssd_plane( h, i_pixel, 0, block_idx_x[i4]*4, block_idx_y[i4]*4 );
      if( CHROMA444 )
      {
          int chromassd = ssd_plane( h, i_pixel, 1, block_idx_x[i4]*4, block_idx_y[i4]*4 )
                        + ssd_plane( h, i_pixel, 2, block_idx_x[i4]*4, block_idx_y[i4]*4 );
          chromassd = ((uint64_t)chromassd * h->mb.i_chroma_lambda2_offset + 128) >> 8;
          i_ssd += chromassd;
      }
  
      if( h->param.b_cabac )
      {
          x264_cabac_t cabac_tmp;
          COPY_CABAC;
          x264_subpartition_size_cabac( h, &cabac_tmp, i4, i_pixel );
          i_bits = ( (uint64_t)cabac_tmp.f8_bits_encoded * i_lambda2 + 128 ) >> 8;
      }
      else
          i_bits = x264_subpartition_size_cavlc( h, i4, i_pixel );
  
      return (i_ssd<<8) + i_bits;
  }
  
  uint64_t x264_rd_cost_part( x264_t *h, int i_lambda2, int i4, int i_pixel )
  {
      uint64_t i_ssd, i_bits;
      int i8 = i4 >> 2;
  
      if( i_pixel == PIXEL_16x16 )
      {
          int i_cost = x264_rd_cost_mb( h, i_lambda2 );
          return i_cost;
      }
  
      if( i_pixel > PIXEL_8x8 )
          return x264_rd_cost_subpart( h, i_lambda2, i4, i_pixel );
  
      h->mb.i_cbp_luma = 0;
  
      x264_macroblock_encode_p8x8( h, i8 );
      if( i_pixel == PIXEL_16x8 )
          x264_macroblock_encode_p8x8( h, i8+1 );
      if( i_pixel == PIXEL_8x16 )
          x264_macroblock_encode_p8x8( h, i8+2 );
  
      int ssd_x = 8*(i8&1);
      int ssd_y = 8*(i8>>1);
      i_ssd = ssd_plane( h, i_pixel, 0, ssd_x, ssd_y );
      int chromapix = h->luma2chroma_pixel[i_pixel];
      int chromassd = ssd_plane( h, chromapix, 1, ssd_x>>CHROMA_H_SHIFT, ssd_y>>CHROMA_V_SHIFT )
                    + ssd_plane( h, chromapix, 2, ssd_x>>CHROMA_H_SHIFT, ssd_y>>CHROMA_V_SHIFT );
      i_ssd += ((uint64_t)chromassd * h->mb.i_chroma_lambda2_offset + 128) >> 8;
  
      if( h->param.b_cabac )
      {
          x264_cabac_t cabac_tmp;
          COPY_CABAC;
          x264_partition_size_cabac( h, &cabac_tmp, i8, i_pixel );
          i_bits = ( (uint64_t)cabac_tmp.f8_bits_encoded * i_lambda2 + 128 ) >> 8;
      }
      else
          i_bits = (uint64_t)x264_partition_size_cavlc( h, i8, i_pixel ) * i_lambda2;
  
      return (i_ssd<<8) + i_bits;
  }
  
  static uint64_t x264_rd_cost_i8x8( x264_t *h, int i_lambda2, int i8, int i_mode, pixel edge[4][32] )
  {
      uint64_t i_ssd, i_bits;
      int plane_count = CHROMA444 ? 3 : 1;
      int i_qp = h->mb.i_qp;
      h->mb.i_cbp_luma &= ~(1<<i8);
      h->mb.b_transform_8x8 = 1;
  
      for( int p = 0; p < plane_count; p++ )
      {
          x264_mb_encode_i8x8( h, p, i8, i_qp, i_mode, edge[p], 1 );
          i_qp = h->mb.i_chroma_qp;
      }
  
      i_ssd = ssd_plane( h, PIXEL_8x8, 0, (i8&1)*8, (i8>>1)*8 );
      if( CHROMA444 )
      {
          int chromassd = ssd_plane( h, PIXEL_8x8, 1, (i8&1)*8, (i8>>1)*8 )
                        + ssd_plane( h, PIXEL_8x8, 2, (i8&1)*8, (i8>>1)*8 );
          chromassd = ((uint64_t)chromassd * h->mb.i_chroma_lambda2_offset + 128) >> 8;
          i_ssd += chromassd;
      }
  
      if( h->param.b_cabac )
      {
          x264_cabac_t cabac_tmp;
          COPY_CABAC;
          x264_partition_i8x8_size_cabac( h, &cabac_tmp, i8, i_mode );
          i_bits = ( (uint64_t)cabac_tmp.f8_bits_encoded * i_lambda2 + 128 ) >> 8;
      }
      else
          i_bits = (uint64_t)x264_partition_i8x8_size_cavlc( h, i8, i_mode ) * i_lambda2;
  
      return (i_ssd<<8) + i_bits;
  }
  
  static uint64_t x264_rd_cost_i4x4( x264_t *h, int i_lambda2, int i4, int i_mode )
  {
      uint64_t i_ssd, i_bits;
      int plane_count = CHROMA444 ? 3 : 1;
      int i_qp = h->mb.i_qp;
  
      for( int p = 0; p < plane_count; p++ )
      {
          x264_mb_encode_i4x4( h, p, i4, i_qp, i_mode, 1 );
          i_qp = h->mb.i_chroma_qp;
      }
  
      i_ssd = ssd_plane( h, PIXEL_4x4, 0, block_idx_x[i4]*4, block_idx_y[i4]*4 );
      if( CHROMA444 )
      {
          int chromassd = ssd_plane( h, PIXEL_4x4, 1, block_idx_x[i4]*4, block_idx_y[i4]*4 )
                        + ssd_plane( h, PIXEL_4x4, 2, block_idx_x[i4]*4, block_idx_y[i4]*4 );
          chromassd = ((uint64_t)chromassd * h->mb.i_chroma_lambda2_offset + 128) >> 8;
          i_ssd += chromassd;
      }
  
      if( h->param.b_cabac )
      {
          x264_cabac_t cabac_tmp;
          COPY_CABAC;
          x264_partition_i4x4_size_cabac( h, &cabac_tmp, i4, i_mode );
          i_bits = ( (uint64_t)cabac_tmp.f8_bits_encoded * i_lambda2 + 128 ) >> 8;
      }
      else
          i_bits = (uint64_t)x264_partition_i4x4_size_cavlc( h, i4, i_mode ) * i_lambda2;
  
      return (i_ssd<<8) + i_bits;
  }
  
  static uint64_t x264_rd_cost_chroma( x264_t *h, int i_lambda2, int i_mode, int b_dct )
  {
      uint64_t i_ssd, i_bits;
  
      if( b_dct )
          x264_mb_encode_chroma( h, 0, h->mb.i_chroma_qp );
  
      int chromapix = h->luma2chroma_pixel[PIXEL_16x16];
      i_ssd = ssd_plane( h, chromapix, 1, 0, 0 )
            + ssd_plane( h, chromapix, 2, 0, 0 );
  
      h->mb.i_chroma_pred_mode = i_mode;
  
      if( h->param.b_cabac )
      {
          x264_cabac_t cabac_tmp;
          COPY_CABAC;
          x264_chroma_size_cabac( h, &cabac_tmp );
          i_bits = ( (uint64_t)cabac_tmp.f8_bits_encoded * i_lambda2 + 128 ) >> 8;
      }
      else
          i_bits = (uint64_t)x264_chroma_size_cavlc( h ) * i_lambda2;
  
      return (i_ssd<<8) + i_bits;
  }
  /****************************************************************************
   * Trellis RD quantization
   ****************************************************************************/
  
  #define TRELLIS_SCORE_MAX -1LL // negative marks the node as invalid
  #define TRELLIS_SCORE_BIAS 1LL<<60; // bias so that all valid scores are positive, even after negative contributions from psy
  #define CABAC_SIZE_BITS 8
  #define LAMBDA_BITS 4
  
  /* precalculate the cost of coding various combinations of bits in a single context */
  void x264_rdo_init( void )
  {
      for( int i_prefix = 0; i_prefix < 15; i_prefix++ )
      {
          for( int i_ctx = 0; i_ctx < 128; i_ctx++ )
          {
              int f8_bits = 0;
              uint8_t ctx = i_ctx;
  
              for( int i = 1; i < i_prefix; i++ )
                  f8_bits += x264_cabac_size_decision2( &ctx, 1 );
              if( i_prefix > 0 && i_prefix < 14 )
                  f8_bits += x264_cabac_size_decision2( &ctx, 0 );
              f8_bits += 1 << CABAC_SIZE_BITS; //sign
  
              x264_cabac_size_unary[i_prefix][i_ctx] = f8_bits;
              x264_cabac_transition_unary[i_prefix][i_ctx] = ctx;
          }
      }
      for( int i_ctx = 0; i_ctx < 128; i_ctx++ )
      {
          int f8_bits = 0;
          uint8_t ctx = i_ctx;
  
          for( int i = 0; i < 5; i++ )
              f8_bits += x264_cabac_size_decision2( &ctx, 1 );
          f8_bits += 1 << CABAC_SIZE_BITS; //sign
  
          cabac_size_5ones[i_ctx] = f8_bits;
          cabac_transition_5ones[i_ctx] = ctx;
      }
  }
  
  typedef struct
  {
      uint64_t score;
      int level_idx; // index into level_tree[]
      uint8_t cabac_state[4]; // just contexts 0,4,8,9 of the 10 relevant to coding abs_level_m1
  } trellis_node_t;
  
  typedef struct
  {
      uint16_t next;
      uint16_t abs_level;
  } trellis_level_t;
  
  // TODO:
  // save cabac state between blocks?
  // use trellis' RD score instead of x264_mb_decimate_score?
  // code 8x8 sig/last flags forwards with deadzone and save the contexts at
  //   each position?
  // change weights when using CQMs?
  
  // possible optimizations:
  // make scores fit in 32bit
  // save quantized coefs during rd, to avoid a duplicate trellis in the final encode
  // if trellissing all MBRD modes, finish SSD calculation so we can skip all of
  //   the normal dequant/idct/ssd/cabac
  
  // the unquant_mf here is not the same as dequant_mf:
  // in normal operation (dct->quant->dequant->idct) the dct and idct are not
  // normalized. quant/dequant absorb those scaling factors.
  // in this function, we just do (quant->unquant) and want the output to be
  // comparable to the input. so unquant is the direct inverse of quant,
  // and uses the dct scaling factors, not the idct ones.
  
  #define SIGN(x,y) ((x^(y >> 31))-(y >> 31))
  
  #define SET_LEVEL(ndst, nsrc, l) {\
      if( sizeof(trellis_level_t) == sizeof(uint32_t) )\
          M32( &level_tree[levels_used] ) = pack16to32( nsrc.level_idx, l );\
      else\
          level_tree[levels_used] = (trellis_level_t){ nsrc.level_idx, l };\
      ndst.level_idx = levels_used;\
      levels_used++;\
  }
  
  // encode all values of the dc coef in a block which is known to have no ac
  static NOINLINE
  int trellis_dc_shortcut( int sign_coef, int quant_coef, int unquant_mf, int coef_weight, int lambda2, uint8_t *cabac_state, int cost_sig )
  {
      uint64_t bscore = TRELLIS_SCORE_MAX;
      int ret = 0;
      int q = abs( quant_coef );
      for( int abs_level = q-1; abs_level <= q; abs_level++ )
      {
          int unquant_abs_level = (unquant_mf * abs_level + 128) >> 8;
  
          /* Optimize rounding for DC coefficients in DC-only luma 4x4/8x8 blocks. */
          int d = sign_coef - ((SIGN(unquant_abs_level, sign_coef) + 8)&~15);
          uint64_t score = (uint64_t)d*d * coef_weight;
  
          /* code the proposed level, and count how much entropy it would take */
          if( abs_level )
          {
              unsigned f8_bits = cost_sig;
              int prefix = X264_MIN( abs_level - 1, 14 );
              f8_bits += x264_cabac_size_decision_noup2( cabac_state+1, prefix > 0 );
              f8_bits += x264_cabac_size_unary[prefix][cabac_state[5]];
              if( abs_level >= 15 )
                  f8_bits += bs_size_ue_big( abs_level - 15 ) << CABAC_SIZE_BITS;
              score += (uint64_t)f8_bits * lambda2 >> ( CABAC_SIZE_BITS - LAMBDA_BITS );
          }
  
          COPY2_IF_LT( bscore, score, ret, abs_level );
      }
      return SIGN(ret, sign_coef);
  }
  
  // encode one value of one coef in one context
  static ALWAYS_INLINE
  int trellis_coef( int j, int const_level, int abs_level, int prefix, int suffix_cost,
                    int node_ctx, int level1_ctx, int levelgt1_ctx, uint64_t ssd, int cost_siglast[3],
                    trellis_node_t *nodes_cur, trellis_node_t *nodes_prev,
                    trellis_level_t *level_tree, int levels_used, int lambda2, uint8_t *level_state )
  {
      uint64_t score = nodes_prev[j].score + ssd;
      /* code the proposed level, and count how much entropy it would take */
      unsigned f8_bits = cost_siglast[ j ? 1 : 2 ];
      uint8_t level1_state = (j >= 3) ? nodes_prev[j].cabac_state[level1_ctx>>2] : level_state[level1_ctx];
      f8_bits += x264_cabac_entropy[level1_state ^ (const_level > 1)];
      uint8_t levelgt1_state;
      if( const_level > 1 )
      {
          levelgt1_state = j >= 6 ? nodes_prev[j].cabac_state[levelgt1_ctx-6] : level_state[levelgt1_ctx];
          f8_bits += x264_cabac_size_unary[prefix][levelgt1_state] + suffix_cost;
      }
      else
          f8_bits += 1 << CABAC_SIZE_BITS;
      score += (uint64_t)f8_bits * lambda2 >> ( CABAC_SIZE_BITS - LAMBDA_BITS );
  
      /* save the node if it's better than any existing node with the same cabac ctx */
      if( score < nodes_cur[node_ctx].score )
      {
          nodes_cur[node_ctx].score = score;
          if( j == 2 || (j <= 3 && node_ctx == 4) ) // init from input state
              M32(nodes_cur[node_ctx].cabac_state) = M32(level_state+12);
          else if( j >= 3 )
              M32(nodes_cur[node_ctx].cabac_state) = M32(nodes_prev[j].cabac_state);
          if( j >= 3 ) // skip the transition if we're not going to reuse the context
              nodes_cur[node_ctx].cabac_state[level1_ctx>>2] = x264_cabac_transition[level1_state][const_level > 1];
          if( const_level > 1 && node_ctx == 7 )
              nodes_cur[node_ctx].cabac_state[levelgt1_ctx-6] = x264_cabac_transition_unary[prefix][levelgt1_state];
          nodes_cur[node_ctx].level_idx = nodes_prev[j].level_idx;
          SET_LEVEL( nodes_cur[node_ctx], nodes_prev[j], abs_level );
      }
      return levels_used;
  }
  
  // encode one value of one coef in all contexts, templated by which value that is.
  // in ctx_lo, the set of live nodes is contiguous and starts at ctx0, so return as soon as we've seen one failure.
  // in ctx_hi, they're contiguous within each block of 4 ctxs, but not necessarily starting at the beginning,
  // so exploiting that would be more complicated.
  static NOINLINE
  int trellis_coef0_0( uint64_t ssd0, trellis_node_t *nodes_cur, trellis_node_t *nodes_prev,
                       trellis_level_t *level_tree, int levels_used )
  {
      nodes_cur[0].score = nodes_prev[0].score + ssd0;
      nodes_cur[0].level_idx = nodes_prev[0].level_idx;
      for( int j = 1; j < 4 && (int64_t)nodes_prev[j].score >= 0; j++ )
      {
          nodes_cur[j].score = nodes_prev[j].score;
          if( j >= 3 )
              M32(nodes_cur[j].cabac_state) = M32(nodes_prev[j].cabac_state);
          SET_LEVEL( nodes_cur[j], nodes_prev[j], 0 );
      }
      return levels_used;
  }
  
  static NOINLINE
  int trellis_coef0_1( uint64_t ssd0, trellis_node_t *nodes_cur, trellis_node_t *nodes_prev,
                       trellis_level_t *level_tree, int levels_used )
  {
      for( int j = 1; j < 8; j++ )
          // this branch only affects speed, not function; there's nothing wrong with updating invalid nodes in coef0.
          if( (int64_t)nodes_prev[j].score >= 0 )
          {
              nodes_cur[j].score = nodes_prev[j].score;
              if( j >= 3 )
                  M32(nodes_cur[j].cabac_state) = M32(nodes_prev[j].cabac_state);
              SET_LEVEL( nodes_cur[j], nodes_prev[j], 0 );
          }
      return levels_used;
  }
  
  #define COEF(const_level, ctx_hi, j, ...)\
      if( !j || (int64_t)nodes_prev[j].score >= 0 )\
          levels_used = trellis_coef( j, const_level, abs_level, prefix, suffix_cost, __VA_ARGS__,\
                                      j?ssd1:ssd0, cost_siglast, nodes_cur, nodes_prev,\
                                      level_tree, levels_used, lambda2, level_state );\
      else if( !ctx_hi )\
          return levels_used;
  
  static NOINLINE
  int trellis_coef1_0( uint64_t ssd0, uint64_t ssd1, int cost_siglast[3],
                       trellis_node_t *nodes_cur, trellis_node_t *nodes_prev,
                       trellis_level_t *level_tree, int levels_used, int lambda2,
                       uint8_t *level_state )
  {
      int abs_level = 1, prefix = 1, suffix_cost = 0;
      COEF( 1, 0, 0, 1, 1, 0 );
      COEF( 1, 0, 1, 2, 2, 0 );
      COEF( 1, 0, 2, 3, 3, 0 );
      COEF( 1, 0, 3, 3, 4, 0 );
      return levels_used;
  }
  
  static NOINLINE
  int trellis_coef1_1( uint64_t ssd0, uint64_t ssd1, int cost_siglast[3],
                       trellis_node_t *nodes_cur, trellis_node_t *nodes_prev,
                       trellis_level_t *level_tree, int levels_used, int lambda2,
                       uint8_t *level_state )
  {
      int abs_level = 1, prefix = 1, suffix_cost = 0;
      COEF( 1, 1, 1, 2, 2, 0 );
      COEF( 1, 1, 2, 3, 3, 0 );
      COEF( 1, 1, 3, 3, 4, 0 );
      COEF( 1, 1, 4, 4, 0, 0 );
      COEF( 1, 1, 5, 5, 0, 0 );
      COEF( 1, 1, 6, 6, 0, 0 );
      COEF( 1, 1, 7, 7, 0, 0 );
      return levels_used;
  }
  
  static NOINLINE
  int trellis_coefn_0( int abs_level, uint64_t ssd0, uint64_t ssd1, int cost_siglast[3],
                       trellis_node_t *nodes_cur, trellis_node_t *nodes_prev,
                       trellis_level_t *level_tree, int levels_used, int lambda2,
                       uint8_t *level_state, int levelgt1_ctx )
  {
      int prefix = X264_MIN( abs_level-1, 14 );
      int suffix_cost = abs_level >= 15 ? bs_size_ue_big( abs_level - 15 ) << CABAC_SIZE_BITS : 0;
      COEF( 2, 0, 0, 4, 1, 5 );
      COEF( 2, 0, 1, 4, 2, 5 );
      COEF( 2, 0, 2, 4, 3, 5 );
      COEF( 2, 0, 3, 4, 4, 5 );
      return levels_used;
  }
  
  static NOINLINE
  int trellis_coefn_1( int abs_level, uint64_t ssd0, uint64_t ssd1, int cost_siglast[3],
                       trellis_node_t *nodes_cur, trellis_node_t *nodes_prev,
                       trellis_level_t *level_tree, int levels_used, int lambda2,
                       uint8_t *level_state, int levelgt1_ctx )
  {
      int prefix = X264_MIN( abs_level-1, 14 );
      int suffix_cost = abs_level >= 15 ? bs_size_ue_big( abs_level - 15 ) << CABAC_SIZE_BITS : 0;
      COEF( 2, 1, 1, 4, 2, 5 );
      COEF( 2, 1, 2, 4, 3, 5 );
      COEF( 2, 1, 3, 4, 4, 5 );
      COEF( 2, 1, 4, 5, 0, 6 );
      COEF( 2, 1, 5, 6, 0, 7 );
      COEF( 2, 1, 6, 7, 0, 8 );
      COEF( 2, 1, 7, 7, 0, levelgt1_ctx );
      return levels_used;
  }
  
  static ALWAYS_INLINE
  int quant_trellis_cabac( x264_t *h, dctcoef *dct,
                           udctcoef *quant_mf, udctcoef *quant_bias, const int *unquant_mf,
                           const uint8_t *zigzag, int ctx_block_cat, int lambda2, int b_ac,
                           int b_chroma, int dc, int num_coefs, int idx )
  {
      ALIGNED_ARRAY_N( dctcoef, orig_coefs, [64] );
      ALIGNED_ARRAY_N( dctcoef, quant_coefs, [64] );
      const uint32_t *coef_weight1 = num_coefs == 64 ? x264_dct8_weight_tab : x264_dct4_weight_tab;
      const uint32_t *coef_weight2 = num_coefs == 64 ? x264_dct8_weight2_tab : x264_dct4_weight2_tab;
      const int b_interlaced = MB_INTERLACED;
      uint8_t *cabac_state_sig = &h->cabac.state[ x264_significant_coeff_flag_offset[b_interlaced][ctx_block_cat] ];
      uint8_t *cabac_state_last = &h->cabac.state[ x264_last_coeff_flag_offset[b_interlaced][ctx_block_cat] ];
      int levelgt1_ctx = b_chroma && dc ? 8 : 9;
  
      if( dc )
      {
          if( num_coefs == 16 )
          {
              memcpy( orig_coefs, dct, sizeof(dctcoef)*16 );
              if( !h->quantf.quant_4x4_dc( dct, quant_mf[0] >> 1, quant_bias[0] << 1 ) )
                  return 0;
              h->zigzagf.scan_4x4( quant_coefs, dct );
          }
          else
          {
              memcpy( orig_coefs, dct, sizeof(dctcoef)*num_coefs );
              int nz = h->quantf.quant_2x2_dc( &dct[0], quant_mf[0] >> 1, quant_bias[0] << 1 );
              if( num_coefs == 8 )
                  nz |= h->quantf.quant_2x2_dc( &dct[4], quant_mf[0] >> 1, quant_bias[0] << 1 );
              if( !nz )
                  return 0;
              for( int i = 0; i < num_coefs; i++ )
                  quant_coefs[i] = dct[zigzag[i]];
          }
      }
      else
      {
          if( num_coefs == 64 )
          {
              h->mc.memcpy_aligned( orig_coefs, dct, sizeof(dctcoef)*64 );
              if( !h->quantf.quant_8x8( dct, quant_mf, quant_bias ) )
                  return 0;
              h->zigzagf.scan_8x8( quant_coefs, dct );
          }
          else //if( num_coefs == 16 )
          {
              memcpy( orig_coefs, dct, sizeof(dctcoef)*16 );
              if( !h->quantf.quant_4x4( dct, quant_mf, quant_bias ) )
                  return 0;
              h->zigzagf.scan_4x4( quant_coefs, dct );
          }
      }
  
      int last_nnz = h->quantf.coeff_last[ctx_block_cat]( quant_coefs+b_ac )+b_ac;
      uint8_t *cabac_state = &h->cabac.state[ x264_coeff_abs_level_m1_offset[ctx_block_cat] ];
  
      /* shortcut for dc-only blocks.
       * this doesn't affect the output, but saves some unnecessary computation. */
      if( last_nnz == 0 && !dc )
      {
          int cost_sig = x264_cabac_size_decision_noup2( &cabac_state_sig[0], 1 )
                       + x264_cabac_size_decision_noup2( &cabac_state_last[0], 1 );
          dct[0] = trellis_dc_shortcut( orig_coefs[0], quant_coefs[0], unquant_mf[0], coef_weight2[0], lambda2, cabac_state, cost_sig );
          return !!dct[0];
      }
  
  #if HAVE_MMX && ARCH_X86_64
  #define TRELLIS_ARGS unquant_mf, zigzag, lambda2, last_nnz, orig_coefs, quant_coefs, dct,\
                       cabac_state_sig, cabac_state_last, M64(cabac_state), M16(cabac_state+8)
      if( num_coefs == 16 && !dc )
          if( b_chroma || !h->mb.i_psy_trellis )
              return h->quantf.trellis_cabac_4x4( TRELLIS_ARGS, b_ac );
          else
              return h->quantf.trellis_cabac_4x4_psy( TRELLIS_ARGS, b_ac, h->mb.pic.fenc_dct4[idx&15], h->mb.i_psy_trellis );
      else if( num_coefs == 64 && !dc )
          if( b_chroma || !h->mb.i_psy_trellis )
              return h->quantf.trellis_cabac_8x8( TRELLIS_ARGS, b_interlaced );
          else
              return h->quantf.trellis_cabac_8x8_psy( TRELLIS_ARGS, b_interlaced, h->mb.pic.fenc_dct8[idx&3], h->mb.i_psy_trellis);
      else if( num_coefs == 8 && dc )
          return h->quantf.trellis_cabac_chroma_422_dc( TRELLIS_ARGS );
      else if( dc )
          return h->quantf.trellis_cabac_dc( TRELLIS_ARGS, num_coefs-1 );
  #endif
  
      // (# of coefs) * (# of ctx) * (# of levels tried) = 1024
      // we don't need to keep all of those: (# of coefs) * (# of ctx) would be enough,
      // but it takes more time to remove dead states than you gain in reduced memory.
      trellis_level_t level_tree[64*8*2];
      int levels_used = 1;
      /* init trellis */
      trellis_node_t nodes[2][8];
      trellis_node_t *nodes_cur = nodes[0];
      trellis_node_t *nodes_prev = nodes[1];
      trellis_node_t *bnode;
      for( int j = 1; j < 4; j++ )
          nodes_cur[j].score = TRELLIS_SCORE_MAX;
      nodes_cur[0].score = TRELLIS_SCORE_BIAS;
      nodes_cur[0].level_idx = 0;
      level_tree[0].abs_level = 0;
      level_tree[0].next = 0;
      ALIGNED_4( uint8_t level_state[16] );
      memcpy( level_state, cabac_state, 10 );
      level_state[12] = cabac_state[0]; // packed subset for copying into trellis_node_t
      level_state[13] = cabac_state[4];
      level_state[14] = cabac_state[8];
      level_state[15] = cabac_state[9];
  
      idx &= num_coefs == 64 ? 3 : 15;
  
      // coefs are processed in reverse order, because that's how the abs value is coded.
      // last_coef and significant_coef flags are normally coded in forward order, but
      // we have to reverse them to match the levels.
      // in 4x4 blocks, last_coef and significant_coef use a separate context for each
      // position, so the order doesn't matter, and we don't even have to update their contexts.
      // in 8x8 blocks, some positions share contexts, so we'll just have to hope that
      // cabac isn't too sensitive.
      int i = last_nnz;
  #define TRELLIS_LOOP(ctx_hi)\
      for( ; i >= b_ac; i-- )\
      {\
          /* skip 0s: this doesn't affect the output, but saves some unnecessary computation. */\
          if( !quant_coefs[i] )\
          {\
              /* no need to calculate ssd of 0s: it's the same in all nodes.\
               * no need to modify level_tree for ctx=0: it starts with an infinite loop of 0s.
               * subtracting from one score is equivalent to adding to the rest. */\
              if( !ctx_hi )\
              {\
                  int sigindex = !dc && num_coefs == 64 ? x264_significant_coeff_flag_offset_8x8[b_interlaced][i] :\
                                 b_chroma && dc && num_coefs == 8 ? x264_coeff_flag_offset_chroma_422_dc[i] : i;\
                  uint64_t cost_sig0 = x264_cabac_size_decision_noup2( &cabac_state_sig[sigindex], 0 )\
                                     * (uint64_t)lambda2 >> ( CABAC_SIZE_BITS - LAMBDA_BITS );\
                  nodes_cur[0].score -= cost_sig0;\
              }\
              for( int j = 1; j < (ctx_hi?8:4); j++ )\
                  SET_LEVEL( nodes_cur[j], nodes_cur[j], 0 );\
              continue;\
          }\
  \
          int sign_coef = orig_coefs[zigzag[i]];\
          int abs_coef = abs( sign_coef );\
          int q = abs( quant_coefs[i] );\
          int cost_siglast[3]; /* { zero, nonzero, nonzero-and-last } */\
          XCHG( trellis_node_t*, nodes_cur, nodes_prev );\
          for( int j = ctx_hi; j < 8; j++ )\
              nodes_cur[j].score = TRELLIS_SCORE_MAX;\
  \
          if( i < num_coefs-1 || ctx_hi )\
          {\
              int sigindex  = !dc && num_coefs == 64 ? x264_significant_coeff_flag_offset_8x8[b_interlaced][i] :\
                              b_chroma && dc && num_coefs == 8 ? x264_coeff_flag_offset_chroma_422_dc[i] : i;\
              int lastindex = !dc && num_coefs == 64 ? x264_last_coeff_flag_offset_8x8[i] :\
                              b_chroma && dc && num_coefs == 8 ? x264_coeff_flag_offset_chroma_422_dc[i] : i;\
              cost_siglast[0] = x264_cabac_size_decision_noup2( &cabac_state_sig[sigindex], 0 );\
              int cost_sig1   = x264_cabac_size_decision_noup2( &cabac_state_sig[sigindex], 1 );\
              cost_siglast[1] = x264_cabac_size_decision_noup2( &cabac_state_last[lastindex], 0 ) + cost_sig1;\
              if( !ctx_hi )\
                  cost_siglast[2] = x264_cabac_size_decision_noup2( &cabac_state_last[lastindex], 1 ) + cost_sig1;\
          }\
          else\
          {\
              cost_siglast[0] = cost_siglast[1] = cost_siglast[2] = 0;\
          }\
  \
          /* there are a few cases where increasing the coeff magnitude helps,\
           * but it's only around .003 dB, and skipping them ~doubles the speed of trellis.\
           * could also try q-2: that sometimes helps, but also sometimes decimates blocks\
           * that are better left coded, especially at QP > 40. */\
          uint64_t ssd0[2], ssd1[2];\
          for( int k = 0; k < 2; k++ )\
          {\
              int abs_level = q-1+k;\
              int unquant_abs_level = (((dc?unquant_mf[0]<<1:unquant_mf[zigzag[i]]) * abs_level + 128) >> 8);\
              int d = abs_coef - unquant_abs_level;\
              /* Psy trellis: bias in favor of higher AC coefficients in the reconstructed frame. */\
              if( h->mb.i_psy_trellis && i && !dc && !b_chroma )\
              {\
                  int orig_coef = (num_coefs == 64) ? h->mb.pic.fenc_dct8[idx][zigzag[i]] : h->mb.pic.fenc_dct4[idx][zigzag[i]];\
                  int predicted_coef = orig_coef - sign_coef;\
                  int psy_value = abs(unquant_abs_level + SIGN(predicted_coef, sign_coef));\
                  int psy_weight = coef_weight1[zigzag[i]] * h->mb.i_psy_trellis;\
                  ssd1[k] = (uint64_t)d*d * coef_weight2[zigzag[i]] - psy_weight * psy_value;\
              }\
              else\
              /* FIXME: for i16x16 dc is this weight optimal? */\
                  ssd1[k] = (uint64_t)d*d * (dc?256:coef_weight2[zigzag[i]]);\
              ssd0[k] = ssd1[k];\
              if( !i && !dc && !ctx_hi )\
              {\
                  /* Optimize rounding for DC coefficients in DC-only luma 4x4/8x8 blocks. */\
                  d = sign_coef - ((SIGN(unquant_abs_level, sign_coef) + 8)&~15);\
                  ssd0[k] = (uint64_t)d*d * coef_weight2[zigzag[i]];\
              }\
          }\
  \
          /* argument passing imposes some significant overhead here. gcc's interprocedural register allocation isn't up to it. */\
          switch( q )\
          {\
          case 1:\
              ssd1[0] += (uint64_t)cost_siglast[0] * lambda2 >> ( CABAC_SIZE_BITS - LAMBDA_BITS );\
              levels_used = trellis_coef0_##ctx_hi( ssd0[0]-ssd1[0], nodes_cur, nodes_prev, level_tree, levels_used );\
              levels_used = trellis_coef1_##ctx_hi( ssd0[1]-ssd1[0], ssd1[1]-ssd1[0], cost_siglast, nodes_cur, nodes_prev, level_tree, levels_used, lambda2, level_state );\
              goto next##ctx_hi;\
          case 2:\
              levels_used = trellis_coef1_##ctx_hi( ssd0[0], ssd1[0], cost_siglast, nodes_cur, nodes_prev, level_tree, levels_used, lambda2, level_state );\
              levels_used = trellis_coefn_##ctx_hi( q, ssd0[1], ssd1[1], cost_siglast, nodes_cur, nodes_prev, level_tree, levels_used, lambda2, level_state, levelgt1_ctx );\
              goto next1;\
          default:\
              levels_used = trellis_coefn_##ctx_hi( q-1, ssd0[0], ssd1[0], cost_siglast, nodes_cur, nodes_prev, level_tree, levels_used, lambda2, level_state, levelgt1_ctx );\
              levels_used = trellis_coefn_##ctx_hi( q, ssd0[1], ssd1[1], cost_siglast, nodes_cur, nodes_prev, level_tree, levels_used, lambda2, level_state, levelgt1_ctx );\
              goto next1;\
          }\
          next##ctx_hi:;\
      }\
      /* output levels from the best path through the trellis */\
      bnode = &nodes_cur[ctx_hi];\
      for( int j = ctx_hi+1; j < (ctx_hi?8:4); j++ )\
          if( nodes_cur[j].score < bnode->score )\
              bnode = &nodes_cur[j];
  
      // keep 2 versions of the main quantization loop, depending on which subsets of the node_ctxs are live
      // node_ctx 0..3, i.e. having not yet encountered any coefs that might be quantized to >1
      TRELLIS_LOOP(0);
  
      if( bnode == &nodes_cur[0] )
      {
          /* We only need to zero an empty 4x4 block. 8x8 can be
             implicitly emptied via zero nnz, as can dc. */
          if( num_coefs == 16 && !dc )
              memset( dct, 0, 16 * sizeof(dctcoef) );
          return 0;
      }
  
      if( 0 ) // accessible only by goto, not fallthrough
      {
          // node_ctx 1..7 (ctx0 ruled out because we never try both level0 and level2+ on the same coef)
          TRELLIS_LOOP(1);
      }
  
      int level = bnode->level_idx;
      for( i = b_ac; i <= last_nnz; i++ )
      {
          dct[zigzag[i]] = SIGN(level_tree[level].abs_level, dct[zigzag[i]]);
          level = level_tree[level].next;
      }
  
      return 1;
  }
  
  /* FIXME: This is a gigantic hack.  See below.
   *
   * CAVLC is much more difficult to trellis than CABAC.
   *
   * CABAC has only three states to track: significance map, last, and the
   * level state machine.
   * CAVLC, by comparison, has five: coeff_token (trailing + total),
   * total_zeroes, zero_run, and the level state machine.
   *
   * I know of no paper that has managed to design a close-to-optimal trellis
   * that covers all five of these and isn't exponential-time.  As a result, this
   * "trellis" isn't: it's just a QNS search.  Patches welcome for something better.
   * It's actually surprisingly fast, albeit not quite optimal.  It's pretty close
   * though; since CAVLC only has 2^16 possible rounding modes (assuming only two
   * roundings as options), a bruteforce search is feasible.  Testing shows
   * that this QNS is reasonably close to optimal in terms of compression.
   *
   * TODO:
   *  Don't bother changing large coefficients when it wouldn't affect bit cost
   *  (e.g. only affecting bypassed suffix bits).
   *  Don't re-run all parts of CAVLC bit cost calculation when not necessary.
   *  e.g. when changing a coefficient from one non-zero value to another in
   *  such a way that trailing ones and suffix length isn't affected. */
  static ALWAYS_INLINE
  int quant_trellis_cavlc( x264_t *h, dctcoef *dct,
                           const udctcoef *quant_mf, const int *unquant_mf,
                           const uint8_t *zigzag, int ctx_block_cat, int lambda2, int b_ac,
                           int b_chroma, int dc, int num_coefs, int idx, int b_8x8 )
  {
      ALIGNED_16( dctcoef quant_coefs[2][16] );
      ALIGNED_16( dctcoef coefs[16] ) = {0};
      const uint32_t *coef_weight1 = b_8x8 ? x264_dct8_weight_tab : x264_dct4_weight_tab;
      const uint32_t *coef_weight2 = b_8x8 ? x264_dct8_weight2_tab : x264_dct4_weight2_tab;
      int delta_distortion[16];
      int64_t score = 1ULL<<62;
      int i, j;
      const int f = 1<<15;
      int nC = b_chroma && dc ? 3 + (num_coefs>>2)
                              : ct_index[x264_mb_predict_non_zero_code( h, !b_chroma && dc ? (idx - LUMA_DC)*16 : idx )];
  
      /* Code for handling 8x8dct -> 4x4dct CAVLC munging.  Input/output use a different
       * step/start/end than internal processing. */
      int step = 1;
      int start = b_ac;
      int end = num_coefs - 1;
      if( b_8x8 )
      {
          start = idx&3;
          end = 60 + start;
          step = 4;
      }
      idx &= 15;
  
      lambda2 <<= LAMBDA_BITS;
  
      /* Find last non-zero coefficient. */
      for( i = end; i >= start; i -= step )
          if( (unsigned)(dct[zigzag[i]] * (dc?quant_mf[0]>>1:quant_mf[zigzag[i]]) + f-1) >= 2*f )
              break;
  
      if( i < start )
          goto zeroblock;
  
      /* Prepare for QNS search: calculate distortion caused by each DCT coefficient
       * rounding to be searched.
       *
       * We only search two roundings (nearest and nearest-1) like in CABAC trellis,
       * so we just store the difference in distortion between them. */
      int last_nnz = b_8x8 ? i >> 2 : i;
      int coef_mask = 0;
      int round_mask = 0;
      for( i = b_ac, j = start; i <= last_nnz; i++, j += step )
      {
          int coef = dct[zigzag[j]];
          int abs_coef = abs(coef);
          int sign = coef < 0 ? -1 : 1;
          int nearest_quant = ( f + abs_coef * (dc?quant_mf[0]>>1:quant_mf[zigzag[j]]) ) >> 16;
          quant_coefs[1][i] = quant_coefs[0][i] = sign * nearest_quant;
          coefs[i] = quant_coefs[1][i];
          if( nearest_quant )
          {
              /* We initialize the trellis with a deadzone halfway between nearest rounding
               * and always-round-down.  This gives much better results than initializing to either
               * extreme.
               * FIXME: should we initialize to the deadzones used by deadzone quant? */
              int deadzone_quant = ( f/2 + abs_coef * (dc?quant_mf[0]>>1:quant_mf[zigzag[j]]) ) >> 16;
              int unquant1 = (((dc?unquant_mf[0]<<1:unquant_mf[zigzag[j]]) * (nearest_quant-0) + 128) >> 8);
              int unquant0 = (((dc?unquant_mf[0]<<1:unquant_mf[zigzag[j]]) * (nearest_quant-1) + 128) >> 8);
              int d1 = abs_coef - unquant1;
              int d0 = abs_coef - unquant0;
              delta_distortion[i] = (d0*d0 - d1*d1) * (dc?256:coef_weight2[zigzag[j]]);
  
              /* Psy trellis: bias in favor of higher AC coefficients in the reconstructed frame. */
              if( h->mb.i_psy_trellis && j && !dc && !b_chroma )
              {
                  int orig_coef = b_8x8 ? h->mb.pic.fenc_dct8[idx>>2][zigzag[j]] : h->mb.pic.fenc_dct4[idx][zigzag[j]];
                  int predicted_coef = orig_coef - coef;
                  int psy_weight = coef_weight1[zigzag[j]];
                  int psy_value0 = h->mb.i_psy_trellis * abs(predicted_coef + unquant0 * sign);
                  int psy_value1 = h->mb.i_psy_trellis * abs(predicted_coef + unquant1 * sign);
                  delta_distortion[i] += (psy_value0 - psy_value1) * psy_weight;
              }
  
              quant_coefs[0][i] = sign * (nearest_quant-1);
              if( deadzone_quant != nearest_quant )
                  coefs[i] = quant_coefs[0][i];
              else
                  round_mask |= 1 << i;
          }
          else
              delta_distortion[i] = 0;
          coef_mask |= (!!coefs[i]) << i;
      }
  
      /* Calculate the cost of the starting state. */
      h->out.bs.i_bits_encoded = 0;
      if( !coef_mask )
          bs_write_vlc( &h->out.bs, x264_coeff0_token[nC] );
      else
          x264_cavlc_block_residual_internal( h, ctx_block_cat, coefs + b_ac, nC );
      score = (int64_t)h->out.bs.i_bits_encoded * lambda2;
  
      /* QNS loop: pick the change that improves RD the most, apply it, repeat.
       * coef_mask and round_mask are used to simplify tracking of nonzeroness
       * and rounding modes chosen. */
      while( 1 )
      {
          int64_t iter_score = score;
          int iter_distortion_delta = 0;
          int iter_coef = -1;
          int iter_mask = coef_mask;
          int iter_round = round_mask;
          for( i = b_ac; i <= last_nnz; i++ )
          {
              if( !delta_distortion[i] )
                  continue;
  
              /* Set up all the variables for this iteration. */
              int cur_round = round_mask ^ (1 << i);
              int round_change = (cur_round >> i)&1;
              int old_coef = coefs[i];
              int new_coef = quant_coefs[round_change][i];
              int cur_mask = (coef_mask&~(1 << i))|(!!new_coef << i);
              int cur_distortion_delta = delta_distortion[i] * (round_change ? -1 : 1);
              int64_t cur_score = cur_distortion_delta;
              coefs[i] = new_coef;
  
              /* Count up bits. */
              h->out.bs.i_bits_encoded = 0;
              if( !cur_mask )
                  bs_write_vlc( &h->out.bs, x264_coeff0_token[nC] );
              else
                  x264_cavlc_block_residual_internal( h, ctx_block_cat, coefs + b_ac, nC );
              cur_score += (int64_t)h->out.bs.i_bits_encoded * lambda2;
  
              coefs[i] = old_coef;
              if( cur_score < iter_score )
              {
                  iter_score = cur_score;
                  iter_coef = i;
                  iter_mask = cur_mask;
                  iter_round = cur_round;
                  iter_distortion_delta = cur_distortion_delta;
              }
          }
          if( iter_coef >= 0 )
          {
              score = iter_score - iter_distortion_delta;
              coef_mask = iter_mask;
              round_mask = iter_round;
              coefs[iter_coef] = quant_coefs[((round_mask >> iter_coef)&1)][iter_coef];
              /* Don't try adjusting coefficients we've already adjusted.
               * Testing suggests this doesn't hurt results -- and sometimes actually helps. */
              delta_distortion[iter_coef] = 0;
          }
          else
              break;
      }
  
      if( coef_mask )
      {
          for( i = b_ac, j = start; i < num_coefs; i++, j += step )
              dct[zigzag[j]] = coefs[i];
          return 1;
      }
  
  zeroblock:
      if( !dc )
      {
          if( b_8x8 )
              for( i = start; i <= end; i+=step )
                  dct[zigzag[i]] = 0;
          else
              memset( dct, 0, 16*sizeof(dctcoef) );
      }
      return 0;
  }
  
  int x264_quant_luma_dc_trellis( x264_t *h, dctcoef *dct, int i_quant_cat, int i_qp, int ctx_block_cat, int b_intra, int idx )
  {
      if( h->param.b_cabac )
          return quant_trellis_cabac( h, dct,
              h->quant4_mf[i_quant_cat][i_qp], h->quant4_bias0[i_quant_cat][i_qp],
              h->unquant4_mf[i_quant_cat][i_qp], x264_zigzag_scan4[MB_INTERLACED],
              ctx_block_cat, h->mb.i_trellis_lambda2[0][b_intra], 0, 0, 1, 16, idx );
  
      return quant_trellis_cavlc( h, dct,
          h->quant4_mf[i_quant_cat][i_qp], h->unquant4_mf[i_quant_cat][i_qp], x264_zigzag_scan4[MB_INTERLACED],
          DCT_LUMA_DC, h->mb.i_trellis_lambda2[0][b_intra], 0, 0, 1, 16, idx, 0 );
  }
  
  static const uint8_t x264_zigzag_scan2x2[4] = { 0, 1, 2, 3 };
  static const uint8_t x264_zigzag_scan2x4[8] = { 0, 2, 1, 4, 6, 3, 5, 7 };
  
  int x264_quant_chroma_dc_trellis( x264_t *h, dctcoef *dct, int i_qp, int b_intra, int idx )
  {
      const uint8_t *zigzag;
      int num_coefs;
      int quant_cat = CQM_4IC+1 - b_intra;
  
      if( CHROMA_FORMAT == CHROMA_422 )
      {
          zigzag = x264_zigzag_scan2x4;
          num_coefs = 8;
      }
      else
      {
          zigzag = x264_zigzag_scan2x2;
          num_coefs = 4;
      }
  
      if( h->param.b_cabac )
          return quant_trellis_cabac( h, dct,
              h->quant4_mf[quant_cat][i_qp], h->quant4_bias0[quant_cat][i_qp],
              h->unquant4_mf[quant_cat][i_qp], zigzag,
              DCT_CHROMA_DC, h->mb.i_trellis_lambda2[1][b_intra], 0, 1, 1, num_coefs, idx );
  
      return quant_trellis_cavlc( h, dct,
          h->quant4_mf[quant_cat][i_qp], h->unquant4_mf[quant_cat][i_qp], zigzag,
          DCT_CHROMA_DC, h->mb.i_trellis_lambda2[1][b_intra], 0, 1, 1, num_coefs, idx, 0 );
  }
  
  int x264_quant_4x4_trellis( x264_t *h, dctcoef *dct, int i_quant_cat,
                              int i_qp, int ctx_block_cat, int b_intra, int b_chroma, int idx )
  {
      static const uint8_t ctx_ac[14] = {0,1,0,0,1,0,0,1,0,0,0,1,0,0};
      int b_ac = ctx_ac[ctx_block_cat];
      if( h->param.b_cabac )
          return quant_trellis_cabac( h, dct,
              h->quant4_mf[i_quant_cat][i_qp], h->quant4_bias0[i_quant_cat][i_qp],
              h->unquant4_mf[i_quant_cat][i_qp], x264_zigzag_scan4[MB_INTERLACED],
              ctx_block_cat, h->mb.i_trellis_lambda2[b_chroma][b_intra], b_ac, b_chroma, 0, 16, idx );
  
      return quant_trellis_cavlc( h, dct,
              h->quant4_mf[i_quant_cat][i_qp], h->unquant4_mf[i_quant_cat][i_qp],
              x264_zigzag_scan4[MB_INTERLACED],
              ctx_block_cat, h->mb.i_trellis_lambda2[b_chroma][b_intra], b_ac, b_chroma, 0, 16, idx, 0 );
  }
  
  int x264_quant_8x8_trellis( x264_t *h, dctcoef *dct, int i_quant_cat,
                              int i_qp, int ctx_block_cat, int b_intra, int b_chroma, int idx )
  {
      if( h->param.b_cabac )
      {
          return quant_trellis_cabac( h, dct,
              h->quant8_mf[i_quant_cat][i_qp], h->quant8_bias0[i_quant_cat][i_qp],
              h->unquant8_mf[i_quant_cat][i_qp], x264_zigzag_scan8[MB_INTERLACED],
              ctx_block_cat, h->mb.i_trellis_lambda2[b_chroma][b_intra], 0, b_chroma, 0, 64, idx );
      }
  
      /* 8x8 CAVLC is split into 4 4x4 blocks */
      int nzaccum = 0;
      for( int i = 0; i < 4; i++ )
      {
          int nz = quant_trellis_cavlc( h, dct,
              h->quant8_mf[i_quant_cat][i_qp], h->unquant8_mf[i_quant_cat][i_qp],
              x264_zigzag_scan8[MB_INTERLACED],
              DCT_LUMA_4x4, h->mb.i_trellis_lambda2[b_chroma][b_intra], 0, b_chroma, 0, 16, idx*4+i, 1 );
          /* Set up nonzero count for future calls */
          h->mb.cache.non_zero_count[x264_scan8[idx*4+i]] = nz;
          nzaccum |= nz;
      }
      STORE_8x8_NNZ( 0, idx, 0 );
      return nzaccum;
  }
  