kc3-lang/freetype/src/sfnt/ttkern.c

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• Hash : 5b26e92a
  Author :
  Date : 2022-02-19T05:26:53
  

  src/sfnt/ttkern.c (tt_face_load_kern): Micro-optimize. A kerning table can be handled by binary search if it has equal entries. Fixes #1132.

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• src/sfnt/ttkern.c

• /****************************************************************************
   *
   * ttkern.c
   *
   *   Load the basic TrueType kerning table.  This doesn't handle
   *   kerning data within the GPOS table at the moment.
   *
   * Copyright (C) 1996-2022 by
   * David Turner, Robert Wilhelm, and Werner Lemberg.
   *
   * This file is part of the FreeType project, and may only be used,
   * modified, and distributed under the terms of the FreeType project
   * license, LICENSE.TXT.  By continuing to use, modify, or distribute
   * this file you indicate that you have read the license and
   * understand and accept it fully.
   *
   */
  
  
  #include <freetype/internal/ftdebug.h>
  #include <freetype/internal/ftstream.h>
  #include <freetype/tttags.h>
  #include "ttkern.h"
  
  #include "sferrors.h"
  
  
    /**************************************************************************
     *
     * The macro FT_COMPONENT is used in trace mode.  It is an implicit
     * parameter of the FT_TRACE() and FT_ERROR() macros, used to print/log
     * messages during execution.
     */
  #undef  FT_COMPONENT
  #define FT_COMPONENT  ttkern
  
  
  #undef  TT_KERN_INDEX
  #define TT_KERN_INDEX( g1, g2 )  ( ( (FT_ULong)(g1) << 16 ) | (g2) )
  
  
    FT_LOCAL_DEF( FT_Error )
    tt_face_load_kern( TT_Face    face,
                       FT_Stream  stream )
    {
      FT_Error   error;
      FT_ULong   table_size;
      FT_Byte*   p;
      FT_Byte*   p_limit;
      FT_UInt    nn, num_tables;
      FT_UInt32  avail = 0, ordered = 0;
  
  
      /* the kern table is optional; exit silently if it is missing */
      error = face->goto_table( face, TTAG_kern, stream, &table_size );
      if ( error )
        goto Exit;
  
      if ( table_size < 4 )  /* the case of a malformed table */
      {
        FT_ERROR(( "tt_face_load_kern:"
                   " kerning table is too small - ignored\n" ));
        error = FT_THROW( Table_Missing );
        goto Exit;
      }
  
      if ( FT_FRAME_EXTRACT( table_size, face->kern_table ) )
      {
        FT_ERROR(( "tt_face_load_kern:"
                   " could not extract kerning table\n" ));
        goto Exit;
      }
  
      face->kern_table_size = table_size;
  
      p       = face->kern_table;
      p_limit = p + table_size;
  
      p         += 2; /* skip version */
      num_tables = FT_NEXT_USHORT( p );
  
      if ( num_tables > 32 ) /* we only support up to 32 sub-tables */
        num_tables = 32;
  
      for ( nn = 0; nn < num_tables; nn++ )
      {
        FT_UInt    num_pairs, length, coverage, format;
        FT_Byte*   p_next;
        FT_UInt32  mask = (FT_UInt32)1UL << nn;
  
  
        if ( p + 6 > p_limit )
          break;
  
        p_next = p;
  
        p       += 2; /* skip version */
        length   = FT_NEXT_USHORT( p );
        coverage = FT_NEXT_USHORT( p );
  
        if ( length <= 6 + 8 )
          break;
  
        p_next += length;
  
        if ( p_next > p_limit )  /* handle broken table */
          p_next = p_limit;
  
        format = coverage >> 8;
  
        /* we currently only support format 0 kerning tables */
        if ( format != 0 )
          goto NextTable;
  
        /* only use horizontal kerning tables */
        if ( ( coverage & 3U ) != 0x0001 ||
             p + 8 > p_next              )
          goto NextTable;
  
        num_pairs = FT_NEXT_USHORT( p );
        p        += 6;
  
        if ( ( p_next - p ) < 6 * (int)num_pairs ) /* handle broken count */
          num_pairs = (FT_UInt)( ( p_next - p ) / 6 );
  
        avail |= mask;
  
        /*
         * Now check whether the pairs in this table are ordered.
         * We then can use binary search.
         */
        if ( num_pairs > 0 )
        {
          FT_ULong  count;
          FT_ULong  old_pair;
  
  
          old_pair = FT_NEXT_ULONG( p );
          p       += 2;
  
          for ( count = num_pairs - 1; count > 0; count-- )
          {
            FT_UInt32  cur_pair;
  
  
            cur_pair = FT_NEXT_ULONG( p );
            if ( cur_pair < old_pair )
              break;
  
            p += 2;
            old_pair = cur_pair;
          }
  
          if ( count == 0 )
            ordered |= mask;
        }
  
      NextTable:
        p = p_next;
      }
  
      face->num_kern_tables = nn;
      face->kern_avail_bits = avail;
      face->kern_order_bits = ordered;
  
    Exit:
      return error;
    }
  
  
    FT_LOCAL_DEF( void )
    tt_face_done_kern( TT_Face  face )
    {
      FT_Stream  stream = face->root.stream;
  
  
      FT_FRAME_RELEASE( face->kern_table );
      face->kern_table_size = 0;
      face->num_kern_tables = 0;
      face->kern_avail_bits = 0;
      face->kern_order_bits = 0;
    }
  
  
    FT_LOCAL_DEF( FT_Int )
    tt_face_get_kerning( TT_Face  face,
                         FT_UInt  left_glyph,
                         FT_UInt  right_glyph )
    {
      FT_Int   result = 0;
      FT_UInt  count, mask;
  
      FT_Byte*  p       = face->kern_table;
      FT_Byte*  p_limit = p + face->kern_table_size;
  
  
      p   += 4;
      mask = 0x0001;
  
      for ( count = face->num_kern_tables;
            count > 0 && p + 6 <= p_limit;
            count--, mask <<= 1 )
      {
        FT_Byte* base     = p;
        FT_Byte* next;
        FT_UInt  version  = FT_NEXT_USHORT( p );
        FT_UInt  length   = FT_NEXT_USHORT( p );
        FT_UInt  coverage = FT_NEXT_USHORT( p );
        FT_UInt  num_pairs;
        FT_Int   value    = 0;
  
        FT_UNUSED( version );
  
  
        next = base + length;
  
        if ( next > p_limit )  /* handle broken table */
          next = p_limit;
  
        if ( ( face->kern_avail_bits & mask ) == 0 )
          goto NextTable;
  
        FT_ASSERT( p + 8 <= next ); /* tested in tt_face_load_kern */
  
        num_pairs = FT_NEXT_USHORT( p );
        p        += 6;
  
        if ( ( next - p ) < 6 * (int)num_pairs )  /* handle broken count  */
          num_pairs = (FT_UInt)( ( next - p ) / 6 );
  
        switch ( coverage >> 8 )
        {
        case 0:
          {
            FT_ULong  key0 = TT_KERN_INDEX( left_glyph, right_glyph );
  
  
            if ( face->kern_order_bits & mask )   /* binary search */
            {
              FT_UInt   min = 0;
              FT_UInt   max = num_pairs;
  
  
              while ( min < max )
              {
                FT_UInt   mid = ( min + max ) >> 1;
                FT_Byte*  q   = p + 6 * mid;
                FT_ULong  key;
  
  
                key = FT_NEXT_ULONG( q );
  
                if ( key == key0 )
                {
                  value = FT_PEEK_SHORT( q );
                  goto Found;
                }
                if ( key < key0 )
                  min = mid + 1;
                else
                  max = mid;
              }
            }
            else /* linear search */
            {
              FT_UInt  count2;
  
  
              for ( count2 = num_pairs; count2 > 0; count2-- )
              {
                FT_ULong  key = FT_NEXT_ULONG( p );
  
  
                if ( key == key0 )
                {
                  value = FT_PEEK_SHORT( p );
                  goto Found;
                }
                p += 2;
              }
            }
          }
          break;
  
         /*
          * We don't support format 2 because we haven't seen a single font
          * using it in real life...
          */
  
        default:
          ;
        }
  
        goto NextTable;
  
      Found:
        if ( coverage & 8 ) /* override or add */
          result = value;
        else
          result += value;
  
      NextTable:
        p = next;
      }
  
      return result;
    }
  
  #undef TT_KERN_INDEX
  
  /* END */
  

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