From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sat, 5 Jun 2004 17:42:50 +0000 (+0000)
Subject: Adjust PageGetMaxOffsetNumber to ensure sane behavior on uninitialized
X-Git-Url: http://waps.l3s.uni-hannover.de/gitweb/?a=commitdiff_plain;h=5d08bff034ecca6de33e6513b651a94f8eba56ff;p=users%2Fbernd%2Fpostgres.git

Adjust PageGetMaxOffsetNumber to ensure sane behavior on uninitialized
pages, even when the macro's result is stored into an unsigned variable.
---

diff --git a/src/include/storage/bufpage.h b/src/include/storage/bufpage.h
index 27d425aac9..4bb17743e3 100644
--- a/src/include/storage/bufpage.h
+++ b/src/include/storage/bufpage.h
@@ -283,13 +283,14 @@ typedef PageHeaderData *PageHeader;
  *		Since offset numbers are 1-based, this is also the number
  *		of items on the page.
  *
- *		NOTE: to ensure sane behavior if the page is not initialized
- *		(pd_lower == 0), cast the unsigned values to int before dividing.
- *		That way we get -1 or so, not a huge positive number...
+ *		NOTE: if the page is not initialized (pd_lower == 0), we must
+ *		return zero to ensure sane behavior.  Accept double evaluation
+ *		of the argument so that we can ensure this.
  */
 #define PageGetMaxOffsetNumber(page) \
-	(((int) (((PageHeader) (page))->pd_lower - SizeOfPageHeaderData)) \
-	 / ((int) sizeof(ItemIdData)))
+	(((PageHeader) (page))->pd_lower <= SizeOfPageHeaderData ? 0 : \
+	 ((((PageHeader) (page))->pd_lower - SizeOfPageHeaderData) \
+	  / sizeof(ItemIdData)))
 
 #define PageGetLSN(page) \
 	(((PageHeader) (page))->pd_lsn)