#define DIFF_CONTEXT_MASK  0x0000ffff  /* Lines of context.  Default if 0 */
#define DIFF_WIDTH_MASK    0x00ff0000  /* side-by-side column width */
#define DIFF_IGNORE_EOLWS  0x01000000  /* Ignore end-of-line whitespace */
#define DIFF_SIDEBYSIDE    0x02000000  /* Generate a side-by-side diff */
#define DIFF_NEWFILE       0x04000000  /* Missing files are as empty files */
#define DIFF_INLINE        0x08000000  /* Inline (not side-by-side) diff */
#define DIFF_HTML          0x10000000  /* Render for HTML */
#define DIFF_LINENO        0x20000000  /* Show line numbers in context diff */

#endif /* INTERFACE */

/*
** Maximum length of a line in a text file.  (8192)
*/
#define LENGTH_MASK_SZ  13

** Append a single line of "diff" output to pOut.
*/
static void appendDiffLine(Blob *pOut, char *zPrefix, DLine *pLine){
  blob_append(pOut, zPrefix, 1);
  blob_append(pOut, pLine->z, pLine->h & LENGTH_MASK);
  blob_append(pOut, "\n", 1);
}

/*
** Append line numbers to the context diff output.  Zero or negative numbers
** are blanks.
*/
static void appendDiffLineno(Blob *pOut, int lnA, int lnB){
  if( lnA>0 ){
    blob_appendf(pOut, "%6d ", lnA);
  }else{
    blob_append(pOut, "       ", 7);
  }
  if( lnB>0 ){
    blob_appendf(pOut, "%6d  ", lnB);
  }else{
    blob_append(pOut, "        ", 8);
  }
}

/*
** Expand the size of aEdit[] array to hold nEdit elements.
*/
static void expandEdit(DContext *p, int nEdit){
  p->aEdit = fossil_realloc(p->aEdit, nEdit*sizeof(int));
  p->nEditAlloc = nEdit;

}


/*
** Given a diff context in which the aEdit[] array has been filled
** in, compute a context diff into pOut.
*/
static void contextDiff(DContext *p, Blob *pOut, int nContext, int showLn){
  DLine *A;     /* Left side of the diff */
  DLine *B;     /* Right side of the diff */  
  int a = 0;    /* Index of next line in A[] */
  int b = 0;    /* Index of next line in B[] */
  int *R;       /* Array of COPY/DELETE/INSERT triples */
  int r;        /* Index into R[] */
  int nr;       /* Number of COPY/DELETE/INSERT triples to process */

      nb += R[r+i*3];
    }
    /*
     * If the patch changes an empty file or results in an empty file,
     * the block header must use 0,0 as position indicator and not 1,0.
     * Otherwise, patch would be confused and may reject the diff.
     */
    if( showLn ) blob_appendf(pOut, "%*s", 15, "");
    blob_appendf(pOut,"@@ -%d,%d +%d,%d @@\n",
      na ? a+skip+1 : 0, na,
      nb ? b+skip+1 : 0, nb);

    /* Show the initial common area */
    a += skip;
    b += skip;
    m = R[r] - skip;
    for(j=0; j<m; j++){
      if( showLn ) appendDiffLineno(pOut, a+j, b+j);
      appendDiffLine(pOut, " ", &A[a+j]);
    }
    a += m;
    b += m;

    /* Show the differences */
    for(i=0; i<nr; i++){
      m = R[r+i*3+1];
      for(j=0; j<m; j++){
        if( showLn ) appendDiffLineno(pOut, a+j, 0);
        appendDiffLine(pOut, "-", &A[a+j]);
      }
      a += m;
      m = R[r+i*3+2];
      for(j=0; j<m; j++){
        if( showLn ) appendDiffLineno(pOut, 0, b+j);
        appendDiffLine(pOut, "+", &B[b+j]);
      }
      b += m;
      if( i<nr-1 ){
        m = R[r+i*3+3];
        for(j=0; j<m; j++){
          if( showLn ) appendDiffLineno(pOut, a+j, b+j);
          appendDiffLine(pOut, " ", &B[b+j]);
        }
        b += m;
        a += m;
      }
    }

    /* Show the final common area */
    assert( nr==i );
    m = R[r+nr*3];
    if( m>nContext ) m = nContext;
    for(j=0; j<m; j++){
      if( showLn ) appendDiffLineno(pOut, a+j, b+j);
      appendDiffLine(pOut, " ", &B[b+j]);
    }
  }
}

/*
** Status of a single output line

/*
** Write up to width characters of pLine into z[].  Translate tabs into
** spaces.  Add a newline if SBS_NEWLINE is set.  Translate HTML characters
** if SBS_HTML is set.  Pad the rendering out width bytes if SBS_PAD is set.
*/
static void sbsWriteText(SbsLine *p, DLine *pLine, unsigned flags){
  int n = pLine->h & LENGTH_MASK;
  int i, j;
  const char *zIn = pLine->z;
  char *z = &p->zLine[p->n];
  int w = p->width;
  if( n>w ) n = w;
  for(i=j=0; i<n; i++){
    char c = zIn[i];
    if( c=='\t' ){

  if( pOut ){
    /* Compute a context or side-by-side diff into pOut */
    if( diffFlags & DIFF_SIDEBYSIDE ){
      int width = diff_width(diffFlags);
      int escHtml = (diffFlags & DIFF_HTML)!=0;
      sbsDiff(&c, pOut, nContext, width, escHtml);
    }else{
      int showLn = (diffFlags & DIFF_LINENO)!=0;
      contextDiff(&c, pOut, nContext, showLn);
    }
    free(c.aFrom);
    free(c.aTo);
    free(c.aEdit);
    return 0;
  }else{
    /* If a context diff is not requested, then return the

/*
** Process diff-related command-line options and return an appropriate
** "diffFlags" integer.  
**
**   --side-by-side|-y      Side-by-side diff.     DIFF_SIDEBYSIDE
**   --context|-c N         N lines of context.    DIFF_CONTEXT_MASK
**   --width|-W N           N character lines.     DIFF_WIDTH_MASK
**   --html                 Format for HTML        DIFF_HTML
**   --linenum|-n           Show line numbers      DIFF_LINENO
*/
int diff_options(void){
  int diffFlags = 0;
  const char *z;
  int f;
  if( find_option("side-by-side","y",0)!=0 ) diffFlags |= DIFF_SIDEBYSIDE;
  if( (z = find_option("context","c",1))!=0 && (f = atoi(z))>0 ){
    if( f > DIFF_CONTEXT_MASK ) f = DIFF_CONTEXT_MASK;
    diffFlags |= f;
  }
  if( (z = find_option("width","W",1))!=0 && (f = atoi(z))>0 ){
    f *= DIFF_CONTEXT_MASK+1;
    if( f > DIFF_WIDTH_MASK ) f = DIFF_CONTEXT_MASK;
    diffFlags |= f;
  }
  if( find_option("html",0,0)!=0 ) diffFlags |= DIFF_HTML;
  if( find_option("linenum","n",0)!=0 ) diffFlags |= DIFF_LINENO;
  return diffFlags;
}

/*
** COMMAND: test-udiff
**
** Print the difference between two files.  The usual diff options apply.

  blob_zero(&out);
  if( diffFlags & DIFF_SIDEBYSIDE ){
    text_diff(&from, &to, &out, diffFlags | DIFF_HTML);
    @ <div class="sbsdiff">
    @ %s(blob_str(&out))
    @ </div>
  }else{
    text_diff(&from, &to, &out, diffFlags | DIFF_LINENO);
    @ %h(blob_str(&out))
  }
  blob_reset(&from);
  blob_reset(&to);
  blob_reset(&out);  
}

  },
  { "div.sbsdiff",
    "side-by-side diff display",
    @   font-family: monospace;
    @   white-space: pre;
  },
  { "div.udiff",
    "context diff display",
    @   font-family: monospace;
    @   white-space: pre;
  },
  { "span.diffchng",
    "changes in a diff",
    @   background-color: #ffffc8;
  },
  { "span.diffadd",
    "added code in a diff",
    @   background-color: #e0ffe0;
  },
  { "span.diffrm",
    "deleted in a diff",
    @   background-color: #ffe0e0;
  },
  { "span.diffhr",
    "suppressed lines in a diff",
    @   color: #0000ff;
  },
  { 0,
    0,