pred(newref,mv_field_sel[1][1],cur,1,          lx<<1,16,8,bx,by>>1,PMV[1][1][0],PMV[1][1][1]>>1,addflag);      }    }    else /* TOP_FIELD or BOTTOM_FIELD */    {      /* field picture */      currentfield = (pict_struct==BOTTOM_FIELD);      if (motion_type==MC_FIELD)      {        /* field-based prediction in field picture */        pred(newref,mv_field_sel[0][1],cur,currentfield,          lx<<1,16,16,bx,by,PMV[0][1][0],PMV[0][1][1],addflag);      }      else if (motion_type==MC_16X8)      {        /* 16 x 8 motion compensation in field picture */        /* upper half */        pred(newref,mv_field_sel[0][1],cur,currentfield,          lx<<1,16,8,bx,by,PMV[0][1][0],PMV[0][1][1],addflag);        /* lower half */        pred(newref,mv_field_sel[1][1],cur,currentfield,          lx<<1,16,8,bx,by+8,PMV[1][1][0],PMV[1][1][1],addflag);      }      else      {        /* invalid motion_type in field picture */        if (!quiet)          fprintf(stderr,"invalid motion_type\n");      }    }  }}/* predict a rectangular block (all three components) * * src:     source frame (Y,U,V) * sfield:  source field select (0: frame or top field, 1: bottom field) * dst:     destination frame (Y,U,V) * dfield:  destination field select (0: frame or top field, 1: bottom field) * * the following values are in luminance picture (frame or field) dimensions * lx:      distance of vertically adjacent pels (selects frame or field pred.) * w,h:     width and height of block (only 16x16 or 16x8 are used) * x,y:     coordinates of destination block * dx,dy:   half pel motion vector * addflag: store or add (= average) prediction */static void pred(src,sfield,dst,dfield,lx,w,h,x,y,dx,dy,addflag)unsigned char *src[];int sfield;unsigned char *dst[];int dfield;int lx;int w, h;int x, y;int dx, dy;int addflag;{  int cc;  for (cc=0; cc<3; cc++)  {    if (cc==1)    {      /* scale for color components */      if (chroma_format==CHROMA420)      {        /* vertical */        h >>= 1; y >>= 1; dy /= 2;      }      if (chroma_format!=CHROMA444)      {        /* horizontal */        w >>= 1; x >>= 1; dx /= 2;        lx >>= 1;      }    }    pred_comp(src[cc]+(sfield?lx>>1:0),dst[cc]+(dfield?lx>>1:0),      lx,w,h,x,y,dx,dy,addflag);  }}/* low level prediction routine * * src:     prediction source * dst:     prediction destination * lx:      line width (for both src and dst) * x,y:     destination coordinates * dx,dy:   half pel motion vector * w,h:     size of prediction block * addflag: store or add prediction */static void pred_comp(src,dst,lx,w,h,x,y,dx,dy,addflag)unsigned char *src;unsigned char *dst;int lx;int w, h;int x, y;int dx, dy;int addflag;{  int xint, xh, yint, yh;  int i, j;  unsigned char *s, *d;  /* half pel scaling */  xint = dx>>1; /* integer part */  xh = dx & 1;  /* half pel flag */  yint = dy>>1;  yh = dy & 1;  /* origins */  s = src + lx*(y+yint) + (x+xint); /* motion vector */  d = dst + lx*y + x;  if (!xh && !yh)    if (addflag)      for (j=0; j<h; j++)      {        for (i=0; i<w; i++)          d[i] = (unsigned int)(d[i]+s[i]+1)>>1;        s+= lx;        d+= lx;      }    else      for (j=0; j<h; j++)      {        for (i=0; i<w; i++)          d[i] = s[i];        s+= lx;        d+= lx;      }  else if (!xh && yh)    if (addflag)      for (j=0; j<h; j++)      {        for (i=0; i<w; i++)          d[i] = (d[i] + ((unsigned int)(s[i]+s[i+lx]+1)>>1)+1)>>1;        s+= lx;        d+= lx;      }    else      for (j=0; j<h; j++)      {        for (i=0; i<w; i++)          d[i] = (unsigned int)(s[i]+s[i+lx]+1)>>1;        s+= lx;        d+= lx;      }  else if (xh && !yh)    if (addflag)      for (j=0; j<h; j++)      {        for (i=0; i<w; i++)          d[i] = (d[i] + ((unsigned int)(s[i]+s[i+1]+1)>>1)+1)>>1;        s+= lx;        d+= lx;      }    else      for (j=0; j<h; j++)      {        for (i=0; i<w; i++)          d[i] = (unsigned int)(s[i]+s[i+1]+1)>>1;        s+= lx;        d+= lx;      }  else /* if (xh && yh) */    if (addflag)      for (j=0; j<h; j++)      {        for (i=0; i<w; i++)          d[i] = (d[i] + ((unsigned int)(s[i]+s[i+1]+s[i+lx]+s[i+lx+1]+2)>>2)+1)>>1;        s+= lx;        d+= lx;      }    else      for (j=0; j<h; j++)      {        for (i=0; i<w; i++)          d[i] = (unsigned int)(s[i]+s[i+1]+s[i+lx]+s[i+lx+1]+2)>>2;        s+= lx;        d+= lx;      }}/* calculate derived motion vectors (DMV) for dual prime prediction * dmvector[2]: differential motion vectors (-1,0,+1) * mvx,mvy: motion vector (for same parity) * * DMV[2][2]: derived motion vectors (for opposite parity) * * uses global variables pict_struct and topfirst * * Notes: *  - all vectors are in field coordinates (even for frame pictures) */static void calc_DMV(DMV,dmvector,mvx,mvy)int DMV[][2];int *dmvector;int mvx, mvy;{  if (pict_struct==FRAME_PICTURE)  {    if (topfirst)    {      /* vector for prediction of top field from bottom field */      DMV[0][0] = ((mvx  +(mvx>0))>>1) + dmvector[0];      DMV[0][1] = ((mvy  +(mvy>0))>>1) + dmvector[1] - 1;      /* vector for prediction of bottom field from top field */      DMV[1][0] = ((3*mvx+(mvx>0))>>1) + dmvector[0];      DMV[1][1] = ((3*mvy+(mvy>0))>>1) + dmvector[1] + 1;    }    else    {      /* vector for prediction of top field from bottom field */      DMV[0][0] = ((3*mvx+(mvx>0))>>1) + dmvector[0];      DMV[0][1] = ((3*mvy+(mvy>0))>>1) + dmvector[1] - 1;      /* vector for prediction of bottom field from top field */      DMV[1][0] = ((mvx  +(mvx>0))>>1) + dmvector[0];      DMV[1][1] = ((mvy  +(mvy>0))>>1) + dmvector[1] + 1;    }  }  else  {    /* vector for prediction from field of opposite 'parity' */    DMV[0][0] = ((mvx+(mvx>0))>>1) + dmvector[0];    DMV[0][1] = ((mvy+(mvy>0))>>1) + dmvector[1];    /* correct for vertical field shift */    if (pict_struct==TOP_FIELD)      DMV[0][1]--;    else      DMV[0][1]++;  }}static void clearblock(cur,i0,j0)unsigned char *cur[];int i0, j0;{  int i, j, w, h;  unsigned char *p;  p = cur[0] + ((pict_struct==BOTTOM_FIELD) ? width : 0) + i0 + width2*j0;  for (j=0; j<16; j++)  {    for (i=0; i<16; i++)      p[i] = 128;    p+= width2;  }  w = h = 16;  if (chroma_format!=CHROMA444)  {    i0>>=1; w>>=1;  }  if (chroma_format==CHROMA420)  {    j0>>=1; h>>=1;  }  p = cur[1] + ((pict_struct==BOTTOM_FIELD) ? chrom_width : 0) + i0             + chrom_width2*j0;  for (j=0; j<h; j++)  {    for (i=0; i<w; i++)      p[i] = 128;    p+= chrom_width2;  }  p = cur[2] + ((pict_struct==BOTTOM_FIELD) ? chrom_width : 0) + i0             + chrom_width2*j0;  for (j=0; j<h; j++)  {    for (i=0; i<w; i++)      p[i] = 128;    p+= chrom_width2;  }}