version 2.5.91

[bison.git] / src / tables.h

diff --git a/src/tables.h b/src/tables.h
index b0fbe9ac4d79a08e639a4a829b1206b9709ba00a..8b5c1fa4c285d54c74879cf5b5db478913c0a845 100644 (file)
--- a/src/tables.h
+++ b/src/tables.h
@@ -1,5 +1,6 @@
 /* Prepare the LALR and GLR parser tables.
-   Copyright (C) 2002, 2004 Free Software Foundation, Inc.
+
+   Copyright (C) 2002, 2004, 2009-2012 Free Software Foundation, Inc.
 
    This file is part of Bison, the GNU Compiler Compiler.
 
@@ -45,48 +46,71 @@
 
    YYSTOS[S] = the symbol number of the symbol that leads to state S.
 
-   YYDEFACT[S] = default rule to reduce with in state s, when YYTABLE
-   doesn't specify something else to do.  Zero means the default is an
-   error.
+   YYFINAL = the state number of the termination state.
+
+   YYTABLE = a vector filled with portions for different uses, found
+   via YYPACT and YYPGOTO, described below.
+
+   YYLAST ( = high) the number of the last element of YYTABLE, i.e.,
+   sizeof (YYTABLE) - 1.
+
+   YYCHECK = a vector indexed in parallel with YYTABLE.  It indicates,
+   in a roundabout way, the bounds of the portion you are trying to
+   examine.
+
+   Suppose that the portion of YYTABLE starts at index P and the index
+   to be examined within the portion is I.  Then if YYCHECK[P+I] != I,
+   I is outside the bounds of what is actually allocated, and the
+   default (from YYDEFACT or YYDEFGOTO) should be used.  Otherwise,
+   YYTABLE[P+I] should be used.
+
+   YYDEFACT[S] = default reduction number in state s.  Performed when
+   YYTABLE doesn't specify something else to do.  Zero means the default
+   is an error.
 
    YYDEFGOTO[I] = default state to go to after a reduction of a rule
    that generates variable NTOKENS + I, except when YYTABLE specifies
    something else to do.
 
    YYPACT[S] = index in YYTABLE of the portion describing state S.
-   The lookahead token's type is used to index that portion to find
-   out what to do.
+   The lookahead token's number, I, is used to index that portion of
+   YYTABLE to find out what action to perform.
+
+   If YYPACT[S] == YYPACT_NINF, if YYPACT[S] + I is outside the bounds
+   of YYTABLE (from 0 to YYLAST), or I is outside the bounds for portion
+   S (that is, YYCHECK[YYPACT[S] + I] != I), then the default action
+   (that is, YYDEFACT[S]) should be used instead of YYTABLE.  Otherwise,
+   the value YYTABLE[YYPACT[S] + I] should be used even if
+   YYPACT[S] < 0.
 
    If the value in YYTABLE is positive, we shift the token and go to
    that state.
 
    If the value is negative, it is minus a rule number to reduce by.
 
-   If the value is zero, the default action from YYDEFACT[S] is used.
+   If the value is YYTABLE_NINF, it's a syntax error.
 
    YYPGOTO[I] = the index in YYTABLE of the portion describing what to
    do after reducing a rule that derives variable I + NTOKENS.  This
    portion is indexed by the parser state number, S, as of before the
-   text for this nonterminal was read.  The value from YYTABLE is the
-   state to go to if the corresponding value in YYCHECK is S.
-
-   YYTABLE = a vector filled with portions for different uses, found
-   via YYPACT and YYPGOTO.
-
-   YYCHECK = a vector indexed in parallel with YYTABLE.  It indicates,
-   in a roundabout way, the bounds of the portion you are trying to
-   examine.
-
-   Suppose that the portion of YYTABLE starts at index P and the index
-   to be examined within the portion is I.  Then if YYCHECK[P+I] != I,
-   I is outside the bounds of what is actually allocated, and the
-   default (from YYDEFACT or YYDEFGOTO) should be used.  Otherwise,
-   YYTABLE[P+I] should be used.
-
-   YYFINAL = the state number of the termination state.
-
-   YYLAST ( = high) the number of the last element of YYTABLE, i.e.,
-   sizeof (YYTABLE) - 1.  */
+   text for this nonterminal was read.
+
+   If YYPGOTO[I] + S is outside the bounds of YYTABLE (from 0 to YYLAST)
+   or if S is outside the bounds of the portion for I (that is,
+   YYCHECK[YYPGOTO[I] + S] != S), then the default state (that is,
+   YYDEFGOTO[I]) should be used instead of YYTABLE.  Otherwise,
+   YYTABLE[YYPGOTO[I] + S] is the state to go to even if YYPGOTO[I] < 0.
+
+   When the above YYPACT, YYPGOTO, and YYCHECK tests determine that a
+   value from YYTABLE should be used, that value is never zero, so it is
+   useless to check for zero.  When those tests indicate that the value
+   from YYDEFACT or YYDEFGOTO should be used instead, the value from
+   YYTABLE *might* be zero, which, as a consequence of the way in which
+   the tables are constructed, also happens to indicate that YYDEFACT or
+   YYDEFGOTO should be used.  However, the YYTABLE value cannot be
+   trusted when the YYDEFACT or YYDEFGOTO value should be used.  In
+   summary, forget about zero values in YYTABLE.
+*/
 
 extern int nvectors;