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Adjust PageGetMaxOffsetNumber to ensure sane behavior on uninitialized

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pages, even when the macro's result is stored into an unsigned variable.
This commit is contained in:
Tom Lane 2004-06-05 17:42:46 +00:00
parent 641c5b565b
commit 24a1e20f14
1 changed files with 7 additions and 6 deletions
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13
src/include/storage/bufpage.h
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@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/include/storage/bufpage.h,v 1.57 2003/12/11 21:21:55 tgl Exp $
* $PostgreSQL: pgsql/src/include/storage/bufpage.h,v 1.58 2004/06/05 17:42:46 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -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)