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.
(cherry picked from commit 8741288212)

Conflicts:

	data/lalr1.java
	data/yacc.c

data/c.m4

@@ -134,6 +134,16 @@ 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.  ##

data/glr.c

@@ -1014,9 +1014,7 @@ 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).  */
@@ -1034,9 +1032,7 @@ 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
@@ -2119,7 +2115,8 @@ yyreportSyntaxError (yyGLRStack* yystackp]b4_user_formals[)
 	  char const *yyprefix = yyexpecting;
 
 	  /* 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.  */

data/lalr1.cc

@@ -841,7 +841,8 @@ b4_error_verbose_if([, int tok])[)
     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.  */

data/lalr1.java

@@ -691,7 +691,8 @@ 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.  */

data/yacc.c

@@ -586,6 +586,12 @@ static const ]b4_int_type_for([b4_table])[ yytable[] =
   ]b4_table[
 };
 
+#define yyis_pact_ninf(yystate) \
+  ]b4_table_value_equals([[pact]], [[yystate]], [b4_pact_ninf])[
+
+#define yyis_table_ninf(yytable_value) \
+  ]b4_table_value_equals([[table]], [[yytable_value]], [b4_table_ninf])[
+
 static const ]b4_int_type_for([b4_check])[ yycheck[] =
 {
   ]b4_check[
@@ -934,7 +940,8 @@ yysyntax_error (char *yyresult, int yystate, int yychar)
       char const *yyprefix = yyexpecting;
 
       /* 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.  */
@@ -1347,7 +1354,7 @@ 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.  */
@@ -1397,7 +1404,7 @@ 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;
@@ -1581,7 +1588,7 @@ yyerrlab1:
   for (;;)
     {
       yyn = yypact[yystate];
-      if (yyn != YYPACT_NINF)
+      if (!yyis_pact_ninf (yyn))
 	{
 	  yyn += YYTERROR;
 	  if (0 <= yyn && yyn <= YYLAST && yycheck[yyn] == YYTERROR)