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Enhance LEMON so that it generates the action table in such a way that no

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range check is needed on the lookahead table to verify that the next input
token is valid.  This makes the lookahead table slightly larger (about 120
bytes) but helps the parser to run faster.

FossilOrigin-Name: 7eb0198d0102e97e4b7ad9e359d95985e55e09c510ea4b360265ac8feb9ed814
This commit is contained in:
drh
2017-12-25 04:15:38 +00:00
parent ef53a9f0af
commit 3a9d6c7156
4 changed files with 61 additions and 36 deletions
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16
tool/lempar.c
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@ -131,19 +131,13 @@
** (A) N = yy_action[ yy_shift_ofst[S] + X ]
** (B) N = yy_default[S]
**
** The (A) formula is preferred. The B formula is used instead if:
** (1) The yy_shift_ofst[S]+X value is out of range, or
** (2) yy_lookahead[yy_shift_ofst[S]+X] is not equal to X, or
** (3) yy_shift_ofst[S] equal YY_SHIFT_USE_DFLT.
** (Implementation note: YY_SHIFT_USE_DFLT is chosen so that
** YY_SHIFT_USE_DFLT+X will be out of range for all possible lookaheads X.
** Hence only tests (1) and (2) need to be evaluated.)
** The (A) formula is preferred. The B formula is used instead if
** yy_lookahead[yy_shift_ofst[S]+X] is not equal to X.
**
** The formulas above are for computing the action when the lookahead is
** a terminal symbol. If the lookahead is a non-terminal (as occurs after
** a reduce action) then the yy_reduce_ofst[] array is used in place of
** the yy_shift_ofst[] array and YY_REDUCE_USE_DFLT is used in place of
** YY_SHIFT_USE_DFLT.
** the yy_shift_ofst[] array.
**
** The following are the tables generated in this section:
**
@ -478,7 +472,8 @@ static unsigned int yy_find_shift_action(
i = yy_shift_ofst[stateno];
assert( iLookAhead!=YYNOCODE );
i += iLookAhead;
if( i<0 || i>=YY_ACTTAB_COUNT || yy_lookahead[i]!=iLookAhead ){
assert( i>=0 && i<sizeof(yy_lookahead)/sizeof(yy_lookahead[0]) );
if( yy_lookahead[i]!=iLookAhead ){
#ifdef YYFALLBACK
YYCODETYPE iFallback; /* Fallback token */
if( iLookAhead<sizeof(yyFallback)/sizeof(yyFallback[0])
@ -541,7 +536,6 @@ static int yy_find_reduce_action(
assert( stateno<=YY_REDUCE_COUNT );
#endif
i = yy_reduce_ofst[stateno];
assert( i!=YY_REDUCE_USE_DFLT );
assert( iLookAhead!=YYNOCODE );
i += iLookAhead;
#ifdef YYERRORSYMBOL