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*** /tmp/,RCSt1a21720 Wed Apr 3 11:49:55 1996
--- page.h Wed Apr 3 08:42:25 1996
***************
*** 158,163
#define PAIRFITS(P,K,D) ((PAIRSIZE((K),(D))) <= FREESPACE((P)))
#define BIGPAIRFITS(P) ((FREESPACE((P)) >= PAIR_OVERHEAD))
#define FREESPACE(P) \
((OFFSET((P)) - PAGE_OVERHEAD - (NUM_ENT((P)) * PAIR_OVERHEAD)))
--- 158,169 -----
#define PAIRFITS(P,K,D) ((PAIRSIZE((K),(D))) <= FREESPACE((P)))
#define BIGPAIRFITS(P) ((FREESPACE((P)) >= PAIR_OVERHEAD))
+ /*
+ * Since these are all unsigned, we need to guarantee that we never go
+ * negative. Offset values are 0-based and overheads are one based (i.e.
+ * one byte of overhead is 1, not 0), so we need to convert OFFSETs to
+ * 1-based counting before subtraction.
+ */
#define FREESPACE(P) \
((OFFSET((P)) + 1 - PAGE_OVERHEAD - (NUM_ENT((P)) * PAIR_OVERHEAD)))
***************
*** 159,165
#define PAIRFITS(P,K,D) ((PAIRSIZE((K),(D))) <= FREESPACE((P)))
#define BIGPAIRFITS(P) ((FREESPACE((P)) >= PAIR_OVERHEAD))
#define FREESPACE(P) \
! ((OFFSET((P)) - PAGE_OVERHEAD - (NUM_ENT((P)) * PAIR_OVERHEAD)))
/*
* Overhead on header pages is just one word -- the length of the
--- 165,171 -----
* 1-based counting before subtraction.
*/
#define FREESPACE(P) \
! ((OFFSET((P)) + 1 - PAGE_OVERHEAD - (NUM_ENT((P)) * PAIR_OVERHEAD)))
/*
* Overhead on header pages is just one word -- the length of the
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