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SQLite training in Houston TX on 2019-11-05 (details)
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Overview
Comment:Further improvements to parser speed by enlarging lookup tables to eliminate the need to do range checking on the index prior to lookup.
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SHA3-256: 47d3e091ae49eb7947af5abef9b5b96b16b86d349e51fe0677795649be6db473
User & Date: drh 2019-08-28 11:31:11
Context
2019-08-28
11:49
Fix an unreachable branch in sqlite3ParserFallback() Closed-Leaf check-in: e059178b user: drh tags: lemon-optimization
11:31
Further improvements to parser speed by enlarging lookup tables to eliminate the need to do range checking on the index prior to lookup. check-in: 47d3e091 user: drh tags: lemon-optimization
02:09
Increase the size of the yy_lookahead table so that it is never necessary to down bounds checking on the index. check-in: bafd8723 user: drh tags: lemon-optimization
Changes
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Changes to tool/lemon.c.

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  fprintf(out, "};\n"); lineno++;
  tplt_xfer(lemp->name,in,out,&lineno);

  /* Generate the table of fallback tokens.
  */
  if( lemp->has_fallback ){
    int mx = lemp->nterminal - 1;


    while( mx>0 && lemp->symbols[mx]->fallback==0 ){ mx--; }
    lemp->tablesize += (mx+1)*szCodeType;
    for(i=0; i<=mx; i++){
      struct symbol *p = lemp->symbols[i];
      if( p->fallback==0 ){
        fprintf(out, "    0,  /* %10s => nothing */\n", p->name);
      }else{
        fprintf(out, "  %3d,  /* %10s => %s */\n", p->fallback->index,







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  fprintf(out, "};\n"); lineno++;
  tplt_xfer(lemp->name,in,out,&lineno);

  /* Generate the table of fallback tokens.
  */
  if( lemp->has_fallback ){
    int mx = lemp->nterminal - 1;
    /* 2019-08-28:  Generate fallback entries for every token to avoid
    ** having to do a range check on the index */
    /* while( mx>0 && lemp->symbols[mx]->fallback==0 ){ mx--; } */
    lemp->tablesize += (mx+1)*szCodeType;
    for(i=0; i<=mx; i++){
      struct symbol *p = lemp->symbols[i];
      if( p->fallback==0 ){
        fprintf(out, "    0,  /* %10s => nothing */\n", p->name);
      }else{
        fprintf(out, "  %3d,  /* %10s => %s */\n", p->fallback->index,

Changes to tool/lempar.c.

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    assert( iLookAhead!=YYNOCODE );
    assert( iLookAhead < YYNTOKEN );
    i += iLookAhead;
    assert( i<(int)YY_NLOOKAHEAD );
    if( yy_lookahead[i]!=iLookAhead ){
#ifdef YYFALLBACK
      YYCODETYPE iFallback;            /* Fallback token */
      if( iLookAhead<sizeof(yyFallback)/sizeof(yyFallback[0])
             && (iFallback = yyFallback[iLookAhead])!=0 ){

#ifndef NDEBUG
        if( yyTraceFILE ){
          fprintf(yyTraceFILE, "%sFALLBACK %s => %s\n",
             yyTracePrompt, yyTokenName[iLookAhead], yyTokenName[iFallback]);
        }
#endif
        assert( yyFallback[iFallback]==0 ); /* Fallback loop must terminate */
................................................................................
        iLookAhead = iFallback;
        continue;
      }
#endif
#ifdef YYWILDCARD
      {
        int j = i - iLookAhead + YYWILDCARD;
        if( 
#if YY_SHIFT_MIN+YYWILDCARD<0
          j>=0 &&
#endif
#if YY_SHIFT_MAX+YYWILDCARD>=YY_ACTTAB_COUNT
          j<YY_ACTTAB_COUNT &&
#endif
          j<(int)(sizeof(yy_lookahead)/sizeof(yy_lookahead[0])) &&
          yy_lookahead[j]==YYWILDCARD && iLookAhead>0
        ){
#ifndef NDEBUG
          if( yyTraceFILE ){
            fprintf(yyTraceFILE, "%sWILDCARD %s => %s\n",
               yyTracePrompt, yyTokenName[iLookAhead],
               yyTokenName[YYWILDCARD]);
          }
#endif /* NDEBUG */







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    assert( iLookAhead!=YYNOCODE );
    assert( iLookAhead < YYNTOKEN );
    i += iLookAhead;
    assert( i<(int)YY_NLOOKAHEAD );
    if( yy_lookahead[i]!=iLookAhead ){
#ifdef YYFALLBACK
      YYCODETYPE iFallback;            /* Fallback token */
      assert( iLookAhead<sizeof(yyFallback)/sizeof(yyFallback[0]) );
      iFallback = yyFallback[iLookAhead];
      if( iFallback!=0 ){
#ifndef NDEBUG
        if( yyTraceFILE ){
          fprintf(yyTraceFILE, "%sFALLBACK %s => %s\n",
             yyTracePrompt, yyTokenName[iLookAhead], yyTokenName[iFallback]);
        }
#endif
        assert( yyFallback[iFallback]==0 ); /* Fallback loop must terminate */
................................................................................
        iLookAhead = iFallback;
        continue;
      }
#endif
#ifdef YYWILDCARD
      {
        int j = i - iLookAhead + YYWILDCARD;







        assert( j<(int)(sizeof(yy_lookahead)/sizeof(yy_lookahead[0])) );
        if( yy_lookahead[j]==YYWILDCARD && iLookAhead>0 ){

#ifndef NDEBUG
          if( yyTraceFILE ){
            fprintf(yyTraceFILE, "%sWILDCARD %s => %s\n",
               yyTracePrompt, yyTokenName[iLookAhead],
               yyTokenName[YYWILDCARD]);
          }
#endif /* NDEBUG */