Some code and documentation improvements.

* data/c.m4 (b4_table_value_equals): New macro to capture
some repeated code.
* data/glr.c (yyis_pact_ninf): Use it here.
(yyis_table_ninf): Likewise.
(yyreportSyntaxError): Improve internal comments.
* data/yacc.c (yyis_pact_ninf): New macro copied from glr.c.
Use it everywhere possible.
(yyis_table_ninf): Likewise.
(yysyntax_error): Improve internal comments.
* data/lalr1.cc (yysyntax_error_): Likewise.
* data/lalr1.java (yysyntax_error): Likewise.
* src/tables.h: Improve comments about yypact, yytable, etc.

7 files changed, 56 insertions, 15 deletions

diff --git a/ChangeLog b/ChangeLog
index b831d116..dc11d517 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,19 @@
+2009-08-25  Joel E. Denny  <jdenny@clemson.edu>
+
+	Some code and documentation improvements.
+	* data/c.m4 (b4_table_value_equals): New macro to capture
+	some repeated code.
+	* data/glr.c (yyis_pact_ninf): Use it here.
+	(yyis_table_ninf): Likewise.
+	(yyreportSyntaxError): Improve internal comments.
+	* data/yacc.c (yyis_pact_ninf): New macro copied from glr.c.
+	Use it everywhere possible.
+	(yyis_table_ninf): Likewise.
+	(yysyntax_error): Improve internal comments.
+	* data/lalr1.cc (yysyntax_error_): Likewise.
+	* data/lalr1.java (yysyntax_error): Likewise.
+	* src/tables.h: Improve comments about yypact, yytable, etc.
+
 2009-08-21  Joel E. Denny  <jdenny@clemson.edu>
 
 	Use locale when quoting.
diff --git a/data/c.m4 b/data/c.m4
index 33a4186c..3ba48db5 100644
--- a/data/c.m4
+++ b/data/c.m4
@@ -157,6 +157,16 @@ m4_define([b4_int_type_for],
 [b4_int_type($1_min, $1_max)])
 
 
+# b4_table_value_equals(TABLE, VALUE, LITERAL)
+# --------------------------------------------
+# Without inducing a comparison warning from the compiler, check if the
+# literal value LITERAL equals VALUE from table TABLE, which must have
+# TABLE_min and TABLE_max defined.
+m4_define([b4_table_value_equals],
+[m4_if(m4_eval($3 < m4_indir([b4_]$1[_min])
+               || m4_indir([b4_]$1[_max]) < $3), [1],
+       [[YYID (0)]],
+       [[((]$2[) == (]$3[))]])])
 
 ## ---------##
 ## Values.  ##
diff --git a/data/glr.c b/data/glr.c
index a4b921f1..b0ad1003 100644
--- a/data/glr.c
+++ b/data/glr.c
@@ -954,9 +954,7 @@ yylhsNonterm (yyRuleNum yyrule)
 }
 
 #define yyis_pact_ninf(yystate) \
-  ]m4_if(m4_eval(b4_pact_ninf < b4_pact_min), [1],
-	 [0],
-	 [((yystate) == YYPACT_NINF)])[
+  ]b4_table_value_equals([[pact]], [[yystate]], [b4_pact_ninf])[
 
 /** True iff LR state STATE has only a default reduction (regardless
  *  of token).  */
@@ -974,9 +972,7 @@ yydefaultAction (yyStateNum yystate)
 }
 
 #define yyis_table_ninf(yytable_value) \
-  ]m4_if(m4_eval(b4_table_ninf < b4_table_min), [1],
-	 [YYID (0)],
-	 [((yytable_value) == YYTABLE_NINF)])[
+  ]b4_table_value_equals([[table]], [[yytable_value]], [b4_table_ninf])[
 
 /** Set *YYACTION to the action to take in YYSTATE on seeing YYTOKEN.
  *  Result R means
@@ -2048,7 +2044,8 @@ yyreportSyntaxError (yyGLRStack* yystackp]b4_user_formals[)
 	  char const *yyarg[YYERROR_VERBOSE_ARGS_MAXIMUM];
 
 	  /* Start YYX at -YYN if negative to avoid negative indexes in
-	     YYCHECK.  */
+	     YYCHECK.  In other words, skip the first -YYN actions for this
+	     state because they are default actions.  */
 	  int yyxbegin = yyn < 0 ? -yyn : 0;
 
 	  /* Stay within bounds of both yycheck and yytname.  */
diff --git a/data/lalr1.cc b/data/lalr1.cc
index 2a9316de..5ce0b47b 100644
--- a/data/lalr1.cc
+++ b/data/lalr1.cc
@@ -954,7 +954,8 @@ b4_error_verbose_if([state_type yystate, int yytoken],
     if (yypact_ninf_ < yyn && yyn <= yylast_)
       {
 	/* Start YYX at -YYN if negative to avoid negative indexes in
-	   YYCHECK.  */
+	   YYCHECK.  In other words, skip the first -YYN actions for this
+	   state because they are default actions.  */
 	int yyxbegin = yyn < 0 ? -yyn : 0;
 
 	/* Stay within bounds of both yycheck and yytname.  */
diff --git a/data/lalr1.java b/data/lalr1.java
index e68650d9..7e274d64 100644
--- a/data/lalr1.java
+++ b/data/lalr1.java
@@ -735,7 +735,8 @@ m4_popdef([b4_at_dollar])])dnl
             StringBuffer res;
 
             /* Start YYX at -YYN if negative to avoid negative indexes in
-               YYCHECK.  */
+               YYCHECK.  In other words, skip the first -YYN actions for this
+               state because they are default actions.  */
             int yyxbegin = yyn < 0 ? -yyn : 0;
 
             /* Stay within bounds of both yycheck and yytname.  */
diff --git a/data/yacc.c b/data/yacc.c
index fa14cc54..96892231 100644
--- a/data/yacc.c
+++ b/data/yacc.c
@@ -525,8 +525,14 @@ static const ]b4_int_type_for([b4_toknum])[ yytoknum[] =
 
 #define YYPACT_NINF ]b4_pact_ninf[
 
+#define yyis_pact_ninf(yystate) \
+  ]b4_table_value_equals([[pact]], [[yystate]], [b4_pact_ninf])[
+
 #define YYTABLE_NINF ]b4_table_ninf[
 
+#define yyis_table_ninf(yytable_value) \
+  ]b4_table_value_equals([[table]], [[yytable_value]], [b4_table_ninf])[
+
 ]b4_parser_tables_define[
 
 #define yyerrok		(yyerrstatus = 0)
@@ -848,7 +854,8 @@ yysyntax_error (char *yyresult, int yystate, int yytoken)
       char const *yyarg[YYERROR_VERBOSE_ARGS_MAXIMUM];
 
       /* Start YYX at -YYN if negative to avoid negative indexes in
-	 YYCHECK.  */
+	 YYCHECK.  In other words, skip the first -YYN actions for this
+	 state because they are default actions.  */
       int yyxbegin = yyn < 0 ? -yyn : 0;
 
       /* Stay within bounds of both yycheck and yytname.  */
@@ -1271,7 +1278,7 @@ yybackup:
 
   /* First try to decide what to do without reference to lookahead token.  */
   yyn = yypact[yystate];
-  if (yyn == YYPACT_NINF)
+  if (yyis_pact_ninf (yyn))
     goto yydefault;
 
   /* Not known => get a lookahead token if don't already have one.  */
@@ -1321,7 +1328,7 @@ yyread_pushed_token:]])[
   yyn = yytable[yyn];
   if (yyn <= 0)
     {
-      if (yyn == 0 || yyn == YYTABLE_NINF)
+      if (yyn == 0 || yyis_table_ninf (yyn))
 	goto yyerrlab;
       yyn = -yyn;
       goto yyreduce;
@@ -1505,7 +1512,7 @@ yyerrlab1:
   for (;;)
     {
       yyn = yypact[yystate];
-      if (yyn != YYPACT_NINF)
+      if (!yyis_pact_ninf (yyn))
 	{
 	  yyn += YYTERROR;
 	  if (0 <= yyn && yyn <= YYLAST && yycheck[yyn] == YYTERROR)
diff --git a/src/tables.h b/src/tables.h
index a44cdb86..b21fa7b0 100644
--- a/src/tables.h
+++ b/src/tables.h
@@ -54,8 +54,15 @@
    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 if YYCHECK indicates that I is
+   outside the bounds of the portion for S, then the default action
+   (from YYDEFACT and YYDEFGOTO) 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.
@@ -64,6 +71,8 @@
 
    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