Fix core dump due to null-pointer dereference in to_char() when datetime

format codes are misapplied to a numeric argument.  (The code still produces
a pretty bogus error message in such cases, but I'll settle for stopping the
crash for now.)  Per bug #4700 from Sergey Burladyan.

Problem exists in all supported branches, so patch all the way back.
In HEAD, also clean up some ugly coding in the nearby cache management
code.

src/backend/utils/adt/formatting.c

 /* -----------------------------------------------------------------------
  * formatting.c
  *
- * $PostgreSQL: pgsql/src/backend/utils/adt/formatting.c,v 1.154 2009/02/07 14:16:45 momjian Exp $
+ * $PostgreSQL: pgsql/src/backend/utils/adt/formatting.c,v 1.155 2009/03/12 00:53:25 tgl Exp $
  *
  *
  *	 Portions Copyright (c) 1999-2009, PostgreSQL Global Development Group
@@ -392,12 +392,10 @@ static int	DCHCounter = 0;
 
 /* global cache for --- number part */
 static NUMCacheEntry NUMCache[NUM_CACHE_FIELDS + 1];
-static NUMCacheEntry *last_NUMCacheEntry;
 
 static int	n_NUMCache = 0;		/* number of entries */
 static int	NUMCounter = 0;
-
-#define MAX_INT32	(2147483600)
+static NUMCacheEntry *last_NUMCacheEntry = NUMCache + 0;
 
 /* ----------
  * For char->date/time conversion
@@ -2765,10 +2763,10 @@ DCH_from_char(FormatNode *node, char *in, TmFromChar *out)
 static DCHCacheEntry *
 DCH_cache_getnew(char *str)
 {
-	DCHCacheEntry *ent = NULL;
+	DCHCacheEntry *ent;
 
-	/* counter overload check  - paranoia? */
-	if (DCHCounter + DCH_CACHE_FIELDS >= MAX_INT32)
+	/* counter overflow check - paranoia? */
+	if (DCHCounter >= (INT_MAX - DCH_CACHE_FIELDS - 1))
 	{
 		DCHCounter = 0;
 
@@ -2777,7 +2775,7 @@ DCH_cache_getnew(char *str)
 	}
 
 	/*
-	 * Cache is full - needs remove any older entry
+	 * If cache is full, remove oldest entry
 	 */
 	if (n_DCHCache > DCH_CACHE_FIELDS)
 	{
@@ -2786,7 +2784,7 @@ DCH_cache_getnew(char *str)
 #ifdef DEBUG_TO_FROM_CHAR
 		elog(DEBUG_elog_output, "cache is full (%d)", n_DCHCache);
 #endif
-		for (ent = DCHCache; ent <= (DCHCache + DCH_CACHE_FIELDS); ent++)
+		for (ent = DCHCache + 1; ent <= (DCHCache + DCH_CACHE_FIELDS); ent++)
 		{
 			if (ent->age < old->age)
 				old = ent;
@@ -2811,18 +2809,16 @@ DCH_cache_getnew(char *str)
 		++n_DCHCache;
 		return ent;
 	}
-
-	return NULL;				/* never */
 }
 
 static DCHCacheEntry *
 DCH_cache_search(char *str)
 {
-	int			i = 0;
+	int			i;
 	DCHCacheEntry *ent;
 
-	/* counter overload check  - paranoia? */
-	if (DCHCounter + DCH_CACHE_FIELDS >= MAX_INT32)
+	/* counter overflow check - paranoia? */
+	if (DCHCounter >= (INT_MAX - DCH_CACHE_FIELDS - 1))
 	{
 		DCHCounter = 0;
 
@@ -2830,16 +2826,13 @@ DCH_cache_search(char *str)
 			ent->age = (++DCHCounter);
 	}
 
-	for (ent = DCHCache; ent <= (DCHCache + DCH_CACHE_FIELDS); ent++)
+	for (i = 0, ent = DCHCache; i < n_DCHCache; i++, ent++)
 	{
-		if (i == n_DCHCache)
-			break;
 		if (strcmp(ent->str, str) == 0)
 		{
 			ent->age = (++DCHCounter);
 			return ent;
 		}
-		i++;
 	}
 
 	return NULL;
@@ -3371,10 +3364,10 @@ do { \
 static NUMCacheEntry *
 NUM_cache_getnew(char *str)
 {
-	NUMCacheEntry *ent = NULL;
+	NUMCacheEntry *ent;
 
-	/* counter overload check  - paranoia? */
-	if (NUMCounter + NUM_CACHE_FIELDS >= MAX_INT32)
+	/* counter overflow check - paranoia? */
+	if (NUMCounter >= (INT_MAX - NUM_CACHE_FIELDS - 1))
 	{
 		NUMCounter = 0;
 
@@ -3383,7 +3376,7 @@ NUM_cache_getnew(char *str)
 	}
 
 	/*
-	 * Cache is full - needs remove any older entry
+	 * If cache is full, remove oldest entry
 	 */
 	if (n_NUMCache > NUM_CACHE_FIELDS)
 	{
@@ -3392,13 +3385,13 @@ NUM_cache_getnew(char *str)
 #ifdef DEBUG_TO_FROM_CHAR
 		elog(DEBUG_elog_output, "Cache is full (%d)", n_NUMCache);
 #endif
-
 		for (ent = NUMCache; ent <= (NUMCache + NUM_CACHE_FIELDS); ent++)
 		{
 			/*
-			 * entry removed via NUM_cache_remove() can be used here
+			 * entry removed via NUM_cache_remove() can be used here,
+			 * which is why it's worth scanning first entry again
 			 */
-			if (*ent->str == '\0')
+			if (ent->str[0] == '\0')
 			{
 				old = ent;
 				break;
@@ -3412,7 +3405,6 @@ NUM_cache_getnew(char *str)
 		StrNCpy(old->str, str, NUM_CACHE_SIZE + 1);
 		/* old->format fill parser */
 		old->age = (++NUMCounter);
-
 		ent = old;
 	}
 	else
@@ -3430,17 +3422,17 @@ NUM_cache_getnew(char *str)
 	zeroize_NUM(&ent->Num);
 
 	last_NUMCacheEntry = ent;
-	return ent;					/* never */
+	return ent;
 }
 
 static NUMCacheEntry *
 NUM_cache_search(char *str)
 {
-	int			i = 0;
+	int			i;
 	NUMCacheEntry *ent;
 
-	/* counter overload check - paranoia? */
-	if (NUMCounter + NUM_CACHE_FIELDS >= MAX_INT32)
+	/* counter overflow check - paranoia? */
+	if (NUMCounter >= (INT_MAX - NUM_CACHE_FIELDS - 1))
 	{
 		NUMCounter = 0;
 
@@ -3448,17 +3440,14 @@ NUM_cache_search(char *str)
 			ent->age = (++NUMCounter);
 	}
 
-	for (ent = NUMCache; ent <= (NUMCache + NUM_CACHE_FIELDS); ent++)
+	for (i = 0, ent = NUMCache; i < n_NUMCache; i++, ent++)
 	{
-		if (i == n_NUMCache)
-			break;
 		if (strcmp(ent->str, str) == 0)
 		{
 			ent->age = (++NUMCounter);
 			last_NUMCacheEntry = ent;
 			return ent;
 		}
-		i++;
 	}
 
 	return NULL;
@@ -3470,7 +3459,7 @@ NUM_cache_remove(NUMCacheEntry *ent)
 #ifdef DEBUG_TO_FROM_CHAR
 	elog(DEBUG_elog_output, "REMOVING ENTRY (%s)", ent->str);
 #endif
-	*ent->str = '\0';
+	ent->str[0] = '\0';
 	ent->age = 0;
 }