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Add bms_prev_member function

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This works very much like the existing bms_last_member function, only it
traverses through the Bitmapset in the opposite direction from the most
significant bit down to the least significant bit.  A special prevbit value of
-1 may be used to have the function determine the most significant bit.  This
is useful for starting a loop.  When there are no members less than prevbit,
the function returns -2 to indicate there are no more members.

Author: David Rowley
Discussion: https://postgr.es/m/CAKJS1f-K=3d5MDASNYFJpUpc20xcBnAwNC1-AOeunhn0OtkWbQ@mail.gmail.com
This commit is contained in:
Alvaro Herrera
2018-04-07 12:01:11 -03:00
parent f16241bef7
commit 5c0675215e
2 changed files with 96 additions and 0 deletions
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src/include/nodes/bitmapset.h
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@@ -99,6 +99,7 @@ extern Bitmapset *bms_join(Bitmapset *a, Bitmapset *b);
/* support for iterating through the integer elements of a set: */
extern int bms_first_member(Bitmapset *a);
extern int bms_next_member(const Bitmapset *a, int prevbit);
extern int bms_prev_member(const Bitmapset *a, int prevbit);
/* support for hashtables using Bitmapsets as keys: */
extern uint32 bms_hash_value(const Bitmapset *a);