switch ( SubstFormat )
    {
    case 1:
      /* no need to check glyph indices/classes used as input for these */
      /* context rules since even invalid glyph indices/classes return  */
      /* meaningful results                                             */

      valid->extra1 = valid->lookup_count;
      OTV_NEST3( ContextSubstFormat1, SubRuleSet, SubRule );
      OTV_RUN( table, valid );
      break;

    case 2:
      /* no need to check glyph indices/classes used as input for these */
      /* context rules since even invalid glyph indices/classes return  */
      /* meaningful results                                             */

      OTV_NEST3( ContextSubstFormat2, SubClassSet, SubClassRule );
      OTV_RUN( table, valid );
      break;

    case 3:
      OTV_NEST1( ContextSubstFormat3 );
      OTV_RUN( table, valid );
      break;

    default:
      FT_INVALID_DATA;
    }

    OTV_EXIT;
  }


  /*************************************************************************/
  /*************************************************************************/
  /*****                                                               *****/
  /*****                    GSUB LOOKUP TYPE 6                         *****/
  /*****                                                               *****/
  /*************************************************************************/
  /*************************************************************************/

  /* sets valid->extra1 (lookup count)            */

  static void
  otv_ChainContextSubst_validate( FT_Bytes       table,
                                  OTV_Validator  valid )
  {
    FT_Bytes  p = table;
    FT_UInt   SubstFormat;


    OTV_NAME_ENTER( "ChainContextSubst" );

    OTV_LIMIT_CHECK( 2 );
    SubstFormat = FT_NEXT_USHORT( p );

    OTV_TRACE(( " (format %d)\n", SubstFormat ));

    switch ( SubstFormat )
    {
    case 1:
      /* no need to check glyph indices/classes used as input for these */
      /* context rules since even invalid glyph indices/classes return  */
      /* meaningful results                                             */

      valid->extra1 = valid->lookup_count;
      OTV_NEST3( ChainContextSubstFormat1,
                 ChainSubRuleSet, ChainSubRule );
      OTV_RUN( table, valid );
      break;

    case 2:
      /* no need to check glyph indices/classes used as input for these */
      /* context rules since even invalid glyph indices/classes return  */
      /* meaningful results                                             */

      OTV_NEST3( ChainContextSubstFormat2,
                 ChainSubClassSet, ChainSubClassRule );
      OTV_RUN( table, valid );
      break;

    case 3:
      OTV_NEST1( ChainContextSubstFormat3 );
      OTV_RUN( table, valid );
      break;

    default:
      FT_INVALID_DATA;
    }

    OTV_EXIT;
  }


  /*************************************************************************/
  /*************************************************************************/
  /*****                                                               *****/
  /*****                    GSUB LOOKUP TYPE 7                         *****/
  /*****                                                               *****/
  /*************************************************************************/
  /*************************************************************************/

  /* uses valid->type_funcs */

  static void
  otv_ExtensionSubst_validate( FT_Bytes       table,
                               OTV_Validator  valid )
  {
    FT_Bytes  p = table;
    FT_UInt   SubstFormat;


    OTV_NAME_ENTER( "ExtensionSubst" );

    OTV_LIMIT_CHECK( 2 );
    SubstFormat = FT_NEXT_USHORT( p );

    OTV_TRACE(( " (format %d)\n", SubstFormat ));

    switch ( SubstFormat )
    {
    case 1:     /* ExtensionSubstFormat1 */
      {
        FT_UInt            ExtensionLookupType, ExtensionOffset;
        OTV_Validate_Func  validate;


        OTV_LIMIT_CHECK( 6 );
        ExtensionLookupType = FT_NEXT_USHORT( p );
        ExtensionOffset     = FT_NEXT_ULONG( p );

        if ( ExtensionLookupType == 0 ||
             ExtensionLookupType == 7 ||
             ExtensionLookupType > 8  )
          FT_INVALID_DATA;

        validate = valid->type_funcs[ExtensionLookupType - 1];
        validate( table + ExtensionOffset, valid );
      }
      break;

    default:
      FT_INVALID_DATA;
    }

    OTV_EXIT;
  }


  /*************************************************************************/
  /*************************************************************************/
  /*****                                                               *****/
  /*****                    GSUB LOOKUP TYPE 8                         *****/
  /*****                                                               *****/
  /*************************************************************************/
  /*************************************************************************/

  /* uses valid->glyph_count */

  static void
  otv_ReverseChainSingleSubst_validate( FT_Bytes       table,
                                        OTV_Validator  valid )
  {
    FT_Bytes  p = table, Coverage;
    FT_UInt   SubstFormat;
    FT_UInt   BacktrackGlyphCount, LookaheadGlyphCount, GlyphCount;


    OTV_NAME_ENTER( "ReverseChainSingleSubst" );

    OTV_LIMIT_CHECK( 2 );
    SubstFormat = FT_NEXT_USHORT( p );

    OTV_TRACE(( " (format %d)\n", SubstFormat ));

    switch ( SubstFormat )
    {
    case 1:     /* ReverseChainSingleSubstFormat1 */
      OTV_LIMIT_CHECK( 4 );
      Coverage            = table + FT_NEXT_USHORT( p );
      BacktrackGlyphCount = FT_NEXT_USHORT( p );

      OTV_TRACE(( " (BacktrackGlyphCount = %d)\n", BacktrackGlyphCount ));

      otv_Coverage_validate( Coverage, valid );

      OTV_LIMIT_CHECK( BacktrackGlyphCount * 2 + 2 );

      for ( ; BacktrackGlyphCount > 0; BacktrackGlyphCount-- )
        otv_Coverage_validate( table + FT_NEXT_USHORT( p ), valid );

      LookaheadGlyphCount = FT_NEXT_USHORT( p );

      OTV_TRACE(( " (LookaheadGlyphCount = %d)\n", LookaheadGlyphCount ));

      OTV_LIMIT_CHECK( LookaheadGlyphCount * 2 + 2 );

      for ( ; LookaheadGlyphCount > 0; LookaheadGlyphCount-- )
        otv_Coverage_validate( table + FT_NEXT_USHORT( p ), valid );

      GlyphCount = FT_NEXT_USHORT( p );

      OTV_TRACE(( " (GlyphCount = %d)\n", GlyphCount ));

      if ( GlyphCount != otv_Coverage_get_count( Coverage ) )
        FT_INVALID_DATA;

      OTV_LIMIT_CHECK( GlyphCount * 2 );

      /* Substitute */
      for ( ; GlyphCount > 0; GlyphCount-- )
        if ( FT_NEXT_USHORT( p ) >= valid->glyph_count )
          FT_INVALID_DATA;

      break;

    default:
      FT_INVALID_DATA;
    }

    OTV_EXIT;
  }


  static const OTV_Validate_Func  otv_gsub_validate_funcs[8] =
  {
    otv_SingleSubst_validate,
    otv_MultipleSubst_validate,
    otv_AlternateSubst_validate,
    otv_LigatureSubst_validate,
    otv_ContextSubst_validate,
    otv_ChainContextSubst_validate,
    otv_ExtensionSubst_validate,
    otv_ReverseChainSingleSubst_validate
  };


  /*************************************************************************/
  /*************************************************************************/
  /*****                                                               *****/
  /*****                          GSUB TABLE                           *****/
  /*****                                                               *****/
  /*************************************************************************/
  /*************************************************************************/

  /* sets valid->type_count  */
  /* sets valid->type_funcs  */
  /* sets valid->glyph_count */

  FT_LOCAL_DEF( void )
  otv_GSUB_validate( FT_Bytes      table,
                     FT_UInt       glyph_count,
                     FT_Validator  ftvalid )
  {
    OTV_ValidatorRec  validrec;
    OTV_Validator     valid = &validrec;
    FT_Bytes          p     = table;
    FT_UInt           ScriptList, FeatureList, LookupList;


    valid->root = ftvalid;

    FT_TRACE3(( "validating GSUB table\n" ));
    OTV_INIT;

    OTV_LIMIT_CHECK( 10 );

    if ( FT_NEXT_ULONG( p ) != 0x10000UL )      /* Version */
      FT_INVALID_DATA;

    ScriptList  = FT_NEXT_USHORT( p );
    FeatureList = FT_NEXT_USHORT( p );
    LookupList  = FT_NEXT_USHORT( p );

    valid->type_count  = 8;
    valid->type_funcs  = (OTV_Validate_Func*)otv_gsub_validate_funcs;
    valid->glyph_count = glyph_count;

    otv_LookupList_validate( table + LookupList,
                             valid );
    otv_FeatureList_validate( table + FeatureList, table + LookupList,
                              valid );
    otv_ScriptList_validate( table + ScriptList, table + FeatureList,
                             valid );

    FT_TRACE4(( "\n" ));
  }


/* END */