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//usr/include/pgsql/server/windowapi.h

/*-------------------------------------------------------------------------
 *
 * windowapi.h
 *	  API for window functions to extract data from their window
 *
 * A window function does not receive its arguments in the normal way
 * (and therefore the concept of strictness is irrelevant).  Instead it
 * receives a "WindowObject", which it can fetch with PG_WINDOW_OBJECT()
 * (note V1 calling convention must be used).  Correct call context can
 * be tested with WindowObjectIsValid().  Although argument values are
 * not passed, the call is correctly set up so that PG_NARGS() can be
 * used and argument type information can be obtained with
 * get_fn_expr_argtype(), get_fn_expr_arg_stable(), etc.
 *
 * Operations on the WindowObject allow the window function to find out
 * the current row number, total number of rows in the partition, etc
 * and to evaluate its argument expression(s) at various rows in the
 * window partition.  See the header comments for each WindowObject API
 * function in nodeWindowAgg.c for details.
 *
 *
 * Portions Copyright (c) 2000-2012, PostgreSQL Global Development Group
 *
 * src/include/windowapi.h
 *
 *-------------------------------------------------------------------------
 */
#ifndef WINDOWAPI_H
#define WINDOWAPI_H

/* values of "seektype" */
#define WINDOW_SEEK_CURRENT 0
#define WINDOW_SEEK_HEAD 1
#define WINDOW_SEEK_TAIL 2

/* this struct is private in nodeWindowAgg.c */
typedef struct WindowObjectData *WindowObject;

#define PG_WINDOW_OBJECT() ((WindowObject) fcinfo->context)

#define WindowObjectIsValid(winobj) \
	((winobj) != NULL && IsA(winobj, WindowObjectData))

extern void *WinGetPartitionLocalMemory(WindowObject winobj, Size sz);

extern int64 WinGetCurrentPosition(WindowObject winobj);
extern int64 WinGetPartitionRowCount(WindowObject winobj);

extern void WinSetMarkPosition(WindowObject winobj, int64 markpos);

extern bool WinRowsArePeers(WindowObject winobj, int64 pos1, int64 pos2);

extern Datum WinGetFuncArgInPartition(WindowObject winobj, int argno,
						 int relpos, int seektype, bool set_mark,
						 bool *isnull, bool *isout);

extern Datum WinGetFuncArgInFrame(WindowObject winobj, int argno,
					 int relpos, int seektype, bool set_mark,
					 bool *isnull, bool *isout);

extern Datum WinGetFuncArgCurrent(WindowObject winobj, int argno,
					 bool *isnull);

#endif   /* WINDOWAPI_H */