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/*!

 *************************************************************************************

 * \file loopFilter.c

 *

 * \brief

 *    Filter to reduce blocking artifacts on a macroblock level.

 *    The filter strength is QP dependent.

 *

 * \author

 *    Contributors:

 *    - Peter List       Peter.List@t-systems.de:  Original code                                 (13-Aug-2001)

 *    - Jani Lainema     Jani.Lainema@nokia.com:   Some bug fixing, removal of recusiveness      (16-Aug-2001)

 *    - Peter List       Peter.List@t-systems.de:  inplace filtering and various simplifications (10-Jan-2002)

 *    - Anthony Joch     anthony@ubvideo.com:      Simplified switching between filters and

 *                                                 non-recursive default filter.                 (08-Jul-2002)

 *    - Cristina Gomila  cristina.gomila@thomson.net: Simplification of the chroma deblocking

 *                                                    from JVT-E089                              (21-Nov-2002)

 *************************************************************************************

 */

#include <stdlib.h>

#include <string.h>

#include <assert.h>

#include "global.h"

#include "image.h"

#include "mb_access.h"

#include "loopfilter.h"

byte mixedModeEdgeFlag, fieldModeFilteringFlag;

/*********************************************************************************************************/

// NOTE: In principle, the alpha and beta tables are calculated with the formulas below

//       Alpha( qp ) = 0.8 * (2^(qp/6)  -  1)

//       Beta ( qp ) = 0.5 * qp  -  7

// The tables actually used have been "hand optimized" though (by Anthony Joch). So, the

// table values might be a little different to formula-generated values. Also, the first

// few values of both tables is set to zero to force the filter off at low qp’s

static const byte ALPHA_TABLE[52]  = {0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,4,4,5,6,  7,8,9,10,12,13,15,17,  20,22,25,28,32,36,40,45,  50,56,63,71,80,90,101,113,  127,144,162,182,203,226,255,255} ;

static const byte  BETA_TABLE[52]  = {0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,2,2,2,3,  3,3,3, 4, 4, 4, 6, 6,   7, 7, 8, 8, 9, 9,10,10,  11,11,12,12,13,13, 14, 14,   15, 15, 16, 16, 17, 17, 18, 18} ;

static const byte CLIP_TAB[52][5]  =

{

  { 0, 0, 0, 0, 0},{ 0, 0, 0, 0, 0},{ 0, 0, 0, 0, 0},{ 0, 0, 0, 0, 0},{ 0, 0, 0, 0, 0},{ 0, 0, 0, 0, 0},{ 0, 0, 0, 0, 0},{ 0, 0, 0, 0, 0},

  { 0, 0, 0, 0, 0},{ 0, 0, 0, 0, 0},{ 0, 0, 0, 0, 0},{ 0, 0, 0, 0, 0},{ 0, 0, 0, 0, 0},{ 0, 0, 0, 0, 0},{ 0, 0, 0, 0, 0},{ 0, 0, 0, 0, 0},

  { 0, 0, 0, 0, 0},{ 0, 0, 0, 1, 1},{ 0, 0, 0, 1, 1},{ 0, 0, 0, 1, 1},{ 0, 0, 0, 1, 1},{ 0, 0, 1, 1, 1},{ 0, 0, 1, 1, 1},{ 0, 1, 1, 1, 1},

  { 0, 1, 1, 1, 1},{ 0, 1, 1, 1, 1},{ 0, 1, 1, 1, 1},{ 0, 1, 1, 2, 2},{ 0, 1, 1, 2, 2},{ 0, 1, 1, 2, 2},{ 0, 1, 1, 2, 2},{ 0, 1, 2, 3, 3},

  { 0, 1, 2, 3, 3},{ 0, 2, 2, 3, 3},{ 0, 2, 2, 4, 4},{ 0, 2, 3, 4, 4},{ 0, 2, 3, 4, 4},{ 0, 3, 3, 5, 5},{ 0, 3, 4, 6, 6},{ 0, 3, 4, 6, 6},

  { 0, 4, 5, 7, 7},{ 0, 4, 5, 8, 8},{ 0, 4, 6, 9, 9},{ 0, 5, 7,10,10},{ 0, 6, 8,11,11},{ 0, 6, 8,13,13},{ 0, 7,10,14,14},{ 0, 8,11,16,16},

  { 0, 9,12,18,18},{ 0,10,13,20,20},{ 0,11,15,23,23},{ 0,13,17,25,25}

} ;

static const char chroma_edge[2][4][4] = //[dir][edge][yuv_format]

{ { {-1, 0, 0, 0},

    {-1,-1,-1, 1},

    {-1, 1, 1, 2},

    {-1,-1,-1, 3}},

  { {-1, 0, 0, 0},

    {-1,-1, 1, 1},

    {-1, 1, 2, 2},

    {-1,-1, 3, 3}}};

void GetStrength(byte Strength[16],struct img_par *img,int MbQAddr,int dir,int edge, int mvlimit,StorablePicture *p);

void EdgeLoop(imgpel** Img, byte Strength[16],struct img_par *img, int MbQAddr, int AlphaC0Offset, int BetaOffset, int dir, int edge, int width, int yuv, int uv, StorablePicture *p);

void DeblockMb(ImageParameters *img, StorablePicture *p, int MbQAddr) ;

/*!

 *****************************************************************************************

 * \brief

 *    Filter all macroblocks in order of increasing macroblock address.

 *****************************************************************************************

 */

void DeblockPicture(ImageParameters *img, StorablePicture *p)

{

  unsigned i;

  for (i=0; i<p->PicSizeInMbs; i++)

  {

    DeblockMb( img, p, i ) ;

  }

}

/*!

 *****************************************************************************************

 * \brief

 *    Deblocking filter for one macroblock.

 *****************************************************************************************

 */

void DeblockMb(ImageParameters *img, StorablePicture *p, int MbQAddr)

{

  int           EdgeCondition;

  int           dir,edge;

  byte          Strength[16];

  int           mb_x, mb_y;

  int           filterNon8x8LumaEdgesFlag[4] = {1,1,1,1};

  int           filterLeftMbEdgeFlag;

  int           filterTopMbEdgeFlag;

  int           fieldModeMbFlag;

  int           mvlimit=4;

  int           i, StrengthSum;

  Macroblock    *MbQ;

  imgpel **imgY   = p->imgY;

  imgpel ***imgUV = p->imgUV;

  int           edge_cr;

  img->DeblockCall = 1;

  get_mb_pos (MbQAddr, &mb_x, &mb_y, IS_LUMA);

  filterLeftMbEdgeFlag  = (mb_x != 0);

  filterTopMbEdgeFlag   = (mb_y != 0);

  MbQ  = &(img->mb_data[MbQAddr]) ; // current Mb

  if (MbQ->mb_type == I8MB)

    assert(MbQ->luma_transform_size_8x8_flag);

  filterNon8x8LumaEdgesFlag[1] =

  filterNon8x8LumaEdgesFlag[3] = !(MbQ->luma_transform_size_8x8_flag);

  if (p->MbaffFrameFlag && mb_y==16 && MbQ->mb_field)

    filterTopMbEdgeFlag = 0;

  fieldModeMbFlag       = (p->structure!=FRAME) || (p->MbaffFrameFlag && MbQ->mb_field);

  if (fieldModeMbFlag)

    mvlimit = 2;

  // return, if filter is disabled

  if (MbQ->LFDisableIdc==1) {

    img->DeblockCall = 0;

    return;

  }

  if (MbQ->LFDisableIdc==2)

  {

    // don't filter at slice boundaries

    filterLeftMbEdgeFlag = MbQ->mbAvailA;

    // if this the bottom of a frame macroblock pair then always filter the top edge

    if (p->MbaffFrameFlag && !MbQ->mb_field && (MbQAddr & 0x01))

      filterTopMbEdgeFlag  = 1;

    else

      filterTopMbEdgeFlag  = MbQ->mbAvailB;

  }

  img->current_mb_nr = MbQAddr;

  CheckAvailabilityOfNeighbors();

  for( dir=0 ; dir<2 ; dir++ )                                             // vertical edges, than horicontal edges

  {

    EdgeCondition = (dir && filterTopMbEdgeFlag) || (!dir && filterLeftMbEdgeFlag); // can not filter beyond picture boundaries

    for( edge=0 ; edge<4 ; edge++ )                                            // first 4 vertical strips of 16 pel

    {                                                                                         // then  4 horicontal

      if( edge || EdgeCondition )

      {

        edge_cr = chroma_edge[dir][edge][p->chroma_format_idc];

        GetStrength(Strength,img,MbQAddr,dir,edge, mvlimit, p); // Strength for 4 blks in 1 stripe

        StrengthSum = Strength[0];

        for (i = 1; i < 16; i++)

        {

          if (StrengthSum) break;

          StrengthSum += Strength[i];

        }

        if( StrengthSum )                      // only if one of the 16 Strength bytes is != 0

        {

          if (filterNon8x8LumaEdgesFlag[edge])

            EdgeLoop( imgY, Strength, img, MbQAddr, MbQ->LFAlphaC0Offset, MbQ->LFBetaOffset, dir, edge, p->size_x, 0, 0, p) ;

          if( (imgUV != NULL) && (edge_cr >= 0))

          {

            EdgeLoop( imgUV[0], Strength, img, MbQAddr, MbQ->LFAlphaC0Offset, MbQ->LFBetaOffset, dir, edge_cr, p->size_x_cr, 1, 0, p) ;

            EdgeLoop( imgUV[1], Strength, img, MbQAddr, MbQ->LFAlphaC0Offset, MbQ->LFBetaOffset, dir, edge_cr, p->size_x_cr, 1, 1, p) ;

          }

        }

        if (dir && !edge && !MbQ->mb_field && mixedModeEdgeFlag) {

          // this is the extra horizontal edge between a frame macroblock pair and a field above it

          img->DeblockCall = 2;

          GetStrength(Strength,img,MbQAddr,dir,4, mvlimit, p); // Strength for 4 blks in 1 stripe

          //if( *((int*)Strength) )                      // only if one of the 4 Strength bytes is != 0

          {

            if (filterNon8x8LumaEdgesFlag[edge])

              EdgeLoop( imgY, Strength, img, MbQAddr, MbQ->LFAlphaC0Offset, MbQ->LFBetaOffset, dir, 4, p->size_x, 0, 0, p) ;

            if( (imgUV != NULL) && (edge_cr >= 0))

            {

              EdgeLoop( imgUV[0], Strength, img, MbQAddr, MbQ->LFAlphaC0Offset, MbQ->LFBetaOffset, dir, 4, p->size_x_cr, 1, 0, p) ;

              EdgeLoop( imgUV[1], Strength, img, MbQAddr, MbQ->LFAlphaC0Offset, MbQ->LFBetaOffset, dir, 4, p->size_x_cr, 1, 1, p) ;

            }

          }

          img->DeblockCall = 1;

        }

      }

    }//end edge

  }//end loop dir

  img->DeblockCall = 0;

}

  /*!

 *********************************************************************************************

 * \brief

 *    returns a buffer of 16 Strength values for one stripe in a mb (for different Frame types)

 *********************************************************************************************

 */

#define ANY_INTRA (MbP->mb_type==I4MB||MbP->mb_type==I16MB||MbP->mb_type==IPCM||MbQ->mb_type==I4MB||MbQ->mb_type==I16MB||MbQ->mb_type==IPCM)

void GetStrength(byte Strength[16],struct img_par *img,int MbQAddr,int dir,int edge, int mvlimit, StorablePicture *p)

{

  int    blkP, blkQ, idx;

  int    blk_x, blk_x2, blk_y, blk_y2 ;

  short  ***list0_mv = p->mv[LIST_0];

  short  ***list1_mv = p->mv[LIST_1];

  char   **list0_refIdxArr = p->ref_idx[LIST_0];

  char   **list1_refIdxArr = p->ref_idx[LIST_1];

  int64  **list0_refPicIdArr = p->ref_pic_id[LIST_0];

  int64  **list1_refPicIdArr = p->ref_pic_id[LIST_1];

  int64    ref_p0,ref_p1,ref_q0,ref_q1;

  int    xQ, xP, yQ, yP;

  int    mb_x, mb_y;

  Macroblock    *MbQ, *MbP;

  PixelPos pixP;

  int dir_m1 = (1 - dir);

  MbQ = &(img->mb_data[MbQAddr]);

  for( idx=0 ; idx<16 ; idx++ )

  {

    xQ = dir ? idx : edge << 2;

    yQ = dir ? (edge < 4 ? edge << 2 : 1) : idx;

    getNeighbour(MbQAddr, xQ - dir_m1, yQ - dir, IS_LUMA, &pixP);

    xP = pixP.x;

    yP = pixP.y;

    MbP = &(img->mb_data[pixP.mb_addr]);

    mixedModeEdgeFlag = (byte) (MbQ->mb_field != MbP->mb_field);

    blkQ = ((yQ>>2)<<2) + (xQ>>2);

    blkP = ((yP>>2)<<2) + (xP>>2);

    if ((p->slice_type==SP_SLICE)||(p->slice_type==SI_SLICE) )

    {

      Strength[idx] = (edge == 0 && (((!p->MbaffFrameFlag && (p->structure==FRAME)) ||

      (p->MbaffFrameFlag && !MbP->mb_field && !MbQ->mb_field)) ||

      ((p->MbaffFrameFlag || (p->structure != FRAME)) && !dir))) ? 4 : 3;

    }

    else

    {

      // Start with Strength=3. or Strength=4 for Mb-edge

      Strength[idx] = (edge == 0 && (((!p->MbaffFrameFlag && (p->structure==FRAME)) ||

        (p->MbaffFrameFlag && !MbP->mb_field && !MbQ->mb_field)) ||

        ((p->MbaffFrameFlag || (p->structure!=FRAME)) && !dir))) ? 4 : 3;

      if(  !(MbP->mb_type==I4MB || MbP->mb_type==I16MB || MbP->mb_type==I8MB || MbP->mb_type==IPCM)

        && !(MbQ->mb_type==I4MB || MbQ->mb_type==I16MB || MbQ->mb_type==I8MB || MbQ->mb_type==IPCM) )

      {

        if( ((MbQ->cbp_blk &  ((int64)1 << blkQ )) != 0) || ((MbP->cbp_blk &  ((int64)1 << blkP)) != 0) )

          Strength[idx] = 2 ;

        else

        {

          // if no coefs, but vector difference >= 1 set Strength=1

          // if this is a mixed mode edge then one set of reference pictures will be frame and the

          // other will be field

          if (mixedModeEdgeFlag)

          {

            (Strength[idx] = 1);

          }

          else

          {

            get_mb_block_pos (MbQAddr, &mb_x, &mb_y);

            blk_y  = (mb_y<<2) + (blkQ >> 2) ;

            blk_x  = (mb_x<<2) + (blkQ  & 3) ;

            blk_y2 = pixP.pos_y >> 2;

            blk_x2 = pixP.pos_x >> 2;

            {

              ref_p0 = list0_refIdxArr[blk_y] [blk_x] <0 ? INT64_MIN : list0_refPicIdArr[blk_y] [blk_x];

              ref_q0 = list0_refIdxArr[blk_y2][blk_x2]<0 ? INT64_MIN : list0_refPicIdArr[blk_y2][blk_x2];

              ref_p1 = list1_refIdxArr[blk_y] [blk_x] <0 ? INT64_MIN : list1_refPicIdArr[blk_y] [blk_x];

              ref_q1 = list1_refIdxArr[blk_y2][blk_x2]<0 ? INT64_MIN : list1_refPicIdArr[blk_y2][blk_x2];

              if ( ((ref_p0==ref_q0) && (ref_p1==ref_q1)) ||

                ((ref_p0==ref_q1) && (ref_p1==ref_q0)))

              {

                Strength[idx]=0;

                // L0 and L1 reference pictures of p0 are different; q0 as well

                if (ref_p0 != ref_p1)

                {

                  // compare MV for the same reference picture

                  if (ref_p0==ref_q0)

                  {

                    Strength[idx] =  (byte) (

                      (iabs( list0_mv[blk_y][blk_x][0] - list0_mv[blk_y2][blk_x2][0]) >= 4) |

                      (iabs( list0_mv[blk_y][blk_x][1] - list0_mv[blk_y2][blk_x2][1]) >= mvlimit) |

                      (iabs( list1_mv[blk_y][blk_x][0] - list1_mv[blk_y2][blk_x2][0]) >= 4) |

                      (iabs( list1_mv[blk_y][blk_x][1] - list1_mv[blk_y2][blk_x2][1]) >= mvlimit));

                  }

                  else

                  {

                    Strength[idx] =  (byte) (

                      (iabs( list0_mv[blk_y][blk_x][0] - list1_mv[blk_y2][blk_x2][0]) >= 4) |

                      (iabs( list0_mv[blk_y][blk_x][1] - list1_mv[blk_y2][blk_x2][1]) >= mvlimit) |

                      (iabs( list1_mv[blk_y][blk_x][0] - list0_mv[blk_y2][blk_x2][0]) >= 4) |

                      (iabs( list1_mv[blk_y][blk_x][1] - list0_mv[blk_y2][blk_x2][1]) >= mvlimit));

                  }

                }

                else

                { // L0 and L1 reference pictures of p0 are the same; q0 as well

                  Strength[idx] = (byte) (

                    ((iabs( list0_mv[blk_y][blk_x][0] - list0_mv[blk_y2][blk_x2][0]) >= 4) |

                    (iabs( list0_mv[blk_y][blk_x][1] - list0_mv[blk_y2][blk_x2][1]) >= mvlimit ) |

                    (iabs( list1_mv[blk_y][blk_x][0] - list1_mv[blk_y2][blk_x2][0]) >= 4) |

                    (iabs( list1_mv[blk_y][blk_x][1] - list1_mv[blk_y2][blk_x2][1]) >= mvlimit))

                    &&

                    ((iabs( list0_mv[blk_y][blk_x][0] - list1_mv[blk_y2][blk_x2][0]) >= 4) |

                    (iabs( list0_mv[blk_y][blk_x][1] - list1_mv[blk_y2][blk_x2][1]) >= mvlimit) |

                    (iabs( list1_mv[blk_y][blk_x][0] - list0_mv[blk_y2][blk_x2][0]) >= 4) |

                    (iabs( list1_mv[blk_y][blk_x][1] - list0_mv[blk_y2][blk_x2][1]) >= mvlimit)));

                }

              }

              else

              {

                Strength[idx] = 1;

              }

            }

          }

        }

      }

    }

  }

}

/*!

 *****************************************************************************************

 * \brief

 *    Filters one edge of 16 (luma) or 8 (chroma) pel

 *****************************************************************************************

 */

void EdgeLoop(imgpel** Img, byte Strength[16],struct img_par *img, int MbQAddr, int AlphaC0Offset, int BetaOffset,

              int dir, int edge, int width, int yuv, int uv, StorablePicture *p)

{

  int      pel, ap = 0, aq = 0, Strng ;

  int      incP, incQ;

  int      C0, c0, Delta, dif, AbsDelta ;

  int      L2 = 0, L1, L0, R0, R1, R2 = 0, RL0, L3, R3 ;

  int      Alpha = 0, Beta = 0 ;

  const byte* ClipTab = NULL;

  int      small_gap;

  int      indexA, indexB;

  int      PelNum;

  int      StrengthIdx;

  imgpel   *SrcPtrP, *SrcPtrQ;

  int      QP;

  int      xP, xQ, yP, yQ;

  Macroblock *MbQ, *MbP;

  PixelPos pixP, pixQ;

  int      bitdepth_scale;

  static const int pelnum_cr[2][4] =  {{0,8,16,16}, {0,8, 8,16}};  //[dir:0=vert, 1=hor.][yuv_format]

  if (!yuv)

    bitdepth_scale = 1<<(img->bitdepth_luma - 8);

  else

    bitdepth_scale = 1<<(img->bitdepth_chroma - 8);

  PelNum = yuv ? pelnum_cr[dir][p->chroma_format_idc] : 16 ;

  for( pel=0 ; pel<PelNum ; pel++ )

  {

    xQ = dir ? pel : edge << 2;

    yQ = dir ? (edge < 4 ? edge << 2 : 1) : pel;

    getNeighbour(MbQAddr, xQ, yQ, yuv, &pixQ);

    getNeighbour(MbQAddr, xQ - (1 - dir), yQ - dir, yuv, &pixP);

    xP = pixP.x;

    yP = pixP.y;

    MbQ = &(img->mb_data[MbQAddr]);

    MbP = &(img->mb_data[pixP.mb_addr]);

    fieldModeFilteringFlag = (byte) (MbQ->mb_field || MbP->mb_field);

    StrengthIdx = (yuv&&(PelNum==8)) ? ((MbQ->mb_field && !MbP->mb_field) ? pel<<1 :((pel>>1)<<2)+(pel&0x01)) : pel;

    if (pixP.available || (MbQ->LFDisableIdc== 0))

    {

      incQ = dir ? ((fieldModeFilteringFlag && !MbQ->mb_field) ? 2 * width : width) : 1;

      incP = dir ? ((fieldModeFilteringFlag && !MbP->mb_field) ? 2 * width : width) : 1;

      SrcPtrQ = &(Img[pixQ.pos_y][pixQ.pos_x]);

      SrcPtrP = &(Img[pixP.pos_y][pixP.pos_x]);

      // Average QP of the two blocks

      QP = yuv ? (MbP->qpc[uv] + MbQ->qpc[uv] + 1) >> 1 : (MbP->qp + MbQ->qp + 1) >> 1;

      indexA = iClip3(0, MAX_QP, QP + AlphaC0Offset);

      indexB = iClip3(0, MAX_QP, QP + BetaOffset);

      Alpha  =ALPHA_TABLE[indexA] * bitdepth_scale;

      Beta   =BETA_TABLE[indexB]  * bitdepth_scale;

      ClipTab=CLIP_TAB[indexA];

      L0  = SrcPtrP[0] ;

      R0  = SrcPtrQ[0] ;

      L1  = SrcPtrP[-incP] ;

      R1  = SrcPtrQ[ incQ] ;

      L2  = SrcPtrP[-incP*2] ;

      R2  = SrcPtrQ[ incQ*2] ;

      L3  = SrcPtrP[-incP*3] ;

      R3  = SrcPtrQ[ incQ*3] ;

      if( (Strng = Strength[StrengthIdx]) != 0)

      {

        AbsDelta  = iabs( Delta = R0 - L0 )  ;

        if( AbsDelta < Alpha )

        {

          C0  = ClipTab[ Strng ] * bitdepth_scale;

          if( ((iabs( R0 - R1) - Beta )  & (iabs(L0 - L1) - Beta )) < 0  )

          {

            if( !yuv)

            {

              aq  = (iabs( R0 - R2) - Beta ) < 0  ;

              ap  = (iabs( L0 - L2) - Beta ) < 0  ;

            }

            RL0             = L0 + R0 ;

            if(Strng == 4 )    // INTRA strong filtering

            {

              if( yuv)  // Chroma

              {

                SrcPtrQ[0] = (imgpel) (((R1 << 1) + R0 + L1 + 2) >> 2);

                SrcPtrP[0] = (imgpel) (((L1 << 1) + L0 + R1 + 2) >> 2);

              }

              else  // Luma

              {

                small_gap = (AbsDelta < ((Alpha >> 2) + 2));

                aq &= small_gap;

                ap &= small_gap;

                SrcPtrQ[0]   = (imgpel) (aq ? ( L1 + ((R1 + RL0) << 1) +  R2 + 4) >> 3 : ((R1 << 1) + R0 + L1 + 2) >> 2) ;

                SrcPtrP[0]   = (imgpel) (ap ? ( R1 + ((L1 + RL0) << 1) +  L2 + 4) >> 3 : ((L1 << 1) + L0 + R1 + 2) >> 2) ;

                SrcPtrQ[ incQ] =  (imgpel) (aq  ? ( R2 + R0 + R1 + L0 + 2) >> 2 : R1);

                SrcPtrP[-incP] =  (imgpel) (ap  ? ( L2 + L1 + L0 + R0 + 2) >> 2 : L1);

                SrcPtrQ[ incQ*2] = (imgpel) (aq ? (((R3 + R2) <<1) + R2 + R1 + RL0 + 4) >> 3 : R2);

                SrcPtrP[-incP*2] = (imgpel) (ap ? (((L3 + L2) <<1) + L2 + L1 + RL0 + 4) >> 3 : L2);

              }

            }

            else                                                     // normal filtering

            {

              c0  = yuv? (C0+1):(C0 + ap + aq) ;

              dif = iClip3( -c0, c0, ( (Delta << 2) + (L1 - R1) + 4) >> 3 ) ;

              if(!yuv)

              {

                SrcPtrP[0]  = (imgpel) iClip3(0, img->max_imgpel_value, L0 + dif) ;

                SrcPtrQ[0]  = (imgpel) iClip3(0, img->max_imgpel_value, R0 - dif) ;

                if( ap )

                  SrcPtrP[-incP] += iClip3( -C0,  C0, ( L2 + ((RL0 + 1) >> 1) - (L1<<1)) >> 1 ) ;