text: /*-------------------------------------------------------------------------
   *
   * list.c
   *	  implementation for PostgreSQL generic linked list package
   *
   *
  <<<<<<< HEAD
   * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
  =======
   * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
  >>>>>>> 0c13ee198f0d690765550fc1c694f9191e9785d6
   * Portions Copyright (c) 1994, Regents of the University of California
   *
   *
   * IDENTIFICATION
   *	  src/backend/nodes/list.c
   *
   *-------------------------------------------------------------------------
   */
  #include "postgres.h"
  
  #include "nodes/pg_list.h"
  
  
  /*
   * Routines to simplify writing assertions about the type of a list; a
   * NIL list is considered to be an empty list of any type.
   */
  #define IsPointerList(l)		((l) == NIL || IsA((l), List))
  #define IsIntegerList(l)		((l) == NIL || IsA((l), IntList))
  #define IsOidList(l)			((l) == NIL || IsA((l), OidList))
  
  #ifdef USE_ASSERT_CHECKING
  /*
   * Check that the specified List is valid (so far as we can tell).
   */
  static void
  check_list_invariants(const List *list)
  {
  	if (list == NIL)
  		return;
  
  	Assert(list->length > 0);
  	Assert(list->head != NULL);
  	Assert(list->tail != NULL);
  
  	Assert(list->type == T_List ||
  		   list->type == T_IntList ||
  		   list->type == T_OidList);
  
  	if (list->length == 1)
  		Assert(list->head == list->tail);
  	if (list->length == 2)
  		Assert(list->head->next == list->tail);
  	Assert(list->tail->next == NULL);
  }
  #else
  #define check_list_invariants(l)
  #endif							/* USE_ASSERT_CHECKING */
  
  /*
   * Return a freshly allocated List. Since empty non-NIL lists are
   * invalid, new_list() also allocates the head cell of the new list:
   * the caller should be sure to fill in that cell's data.
   */
  static List *
  new_list(NodeTag type)
  {
  	List	   *new_list;
  	ListCell   *new_head;
  
  	new_head = (ListCell *) palloc(sizeof(*new_head));
  	new_head->next = NULL;
  	/* new_head->data is left undefined! */
  
  	new_list = (List *) palloc(sizeof(*new_list));
  	new_list->type = type;
  	new_list->length = 1;
  	new_list->head = new_head;
  	new_list->tail = new_head;
  
  	return new_list;
  }
  
  /*
   * Allocate a new cell and make it the head of the specified
   * list. Assumes the list it is passed is non-NIL.
   *
   * The data in the new head cell is undefined; the caller should be
   * sure to fill it in
   */
  static void
  new_head_cell(List *list)
  {
  	ListCell   *new_head;
  
  	new_head = (ListCell *) palloc(sizeof(*new_head));
  	new_head->next = list->head;
  
  	list->head = new_head;
  	list->length++;
  }
  
  /*
   * Allocate a new cell and make it the tail of the specified
   * list. Assumes the list it is passed is non-NIL.
   *
   * The data in the new tail cell is undefined; the caller should be
   * sure to fill it in
   */
  static void
  new_tail_cell(List *list)
  {
  	ListCell   *new_tail;
  
  	new_tail = (ListCell *) palloc(sizeof(*new_tail));
  	new_tail->next = NULL;
  
  	list->tail->next = new_tail;
  	list->tail = new_tail;
  	list->length++;
  }
  
  /*
   * Append a pointer to the list. A pointer to the modified list is
   * returned. Note that this function may or may not destructively
   * modify the list; callers should always use this function's return
   * value, rather than continuing to use the pointer passed as the
   * first argument.
   */
  List *
  lappend(List *list, void *datum)
  {
  	Assert(IsPointerList(list));
  
  	if (list == NIL)
  		list = new_list(T_List);
  	else
  		new_tail_cell(list);
  
  	lfirst(list->tail) = datum;
  	check_list_invariants(list);
  	return list;
  }
  
  /*
   * Append an integer to the specified list. See lappend()
   */
  List *
  lappend_int(List *list, int datum)
  {
  	Assert(IsIntegerList(list));
  
  	if (list == NIL)
  		list = new_list(T_IntList);
  	else
  		new_tail_cell(list);
  
  	lfirst_int(list->tail) = datum;
  	check_list_invariants(list);
  	return list;
  }
  
  /*
   * Append an OID to the specified list. See lappend()
   */
  List *
  lappend_oid(List *list, Oid datum)
  {
  	Assert(IsOidList(list));
  
  	if (list == NIL)
  		list = new_list(T_OidList);
  	else
  		new_tail_cell(list);
  
  	lfirst_oid(list->tail) = datum;
  	check_list_invariants(list);
  	return list;
  }
  
  /*
   * Add a new cell to the list, in the position after 'prev_cell'. The
   * data in the cell is left undefined, and must be filled in by the
   * caller. 'list' is assumed to be non-NIL, and 'prev_cell' is assumed
   * to be non-NULL and a member of 'list'.
   */
  static ListCell *
  add_new_cell(List *list, ListCell *prev_cell)
  {
  	ListCell   *new_cell;
  
  	new_cell = (ListCell *) palloc(sizeof(*new_cell));
  	/* new_cell->data is left undefined! */
  	new_cell->next = prev_cell->next;
  	prev_cell->next = new_cell;
  
  	if (list->tail == prev_cell)
  		list->tail = new_cell;
  
  	list->length++;
  
  	return new_cell;
  }
  
  /*
   * Add a new cell to the specified list (which must be non-NIL);
   * it will be placed after the list cell 'prev' (which must be
   * non-NULL and a member of 'list'). The data placed in the new cell
   * is 'datum'. The newly-constructed cell is returned.
   */
  ListCell *
  lappend_cell(List *list, ListCell *prev, void *datum)
  {
  	ListCell   *new_cell;
  
  	Assert(IsPointerList(list));
  
  	new_cell = add_new_cell(list, prev);
  	lfirst(new_cell) = datum;
  	check_list_invariants(list);
  	return new_cell;
  }
  
  ListCell *
  lappend_cell_int(List *list, ListCell *prev, int datum)
  {
  	ListCell   *new_cell;
  
  	Assert(IsIntegerList(list));
  
  	new_cell = add_new_cell(list, prev);
  	lfirst_int(new_cell) = datum;
  	check_list_invariants(list);
  	return new_cell;
  }
  
  ListCell *
  lappend_cell_oid(List *list, ListCell *prev, Oid datum)
  {
  	ListCell   *new_cell;
  
  	Assert(IsOidList(list));
  
  	new_cell = add_new_cell(list, prev);
  	lfirst_oid(new_cell) = datum;
  	check_list_invariants(list);
  	return new_cell;
  }
  
  /*
   * Prepend a new element to the list. A pointer to the modified list
   * is returned. Note that this function may or may not destructively
   * modify the list; callers should always use this function's return
   * value, rather than continuing to use the pointer passed as the
   * second argument.
   *
   * Caution: before Postgres 8.0, the original List was unmodified and
   * could be considered to retain its separate identity.  This is no longer
   * the case.
   */
  List *
  lcons(void *datum, List *list)
  {
  	Assert(IsPointerList(list));
  
  	if (list == NIL)
  		list = new_list(T_List);
  	else
  		new_head_cell(list);
  
  	lfirst(list->head) = datum;
  	check_list_invariants(list);
  	return list;
  }
  
  /*
   * Prepend an integer to the list. See lcons()
   */
  List *
  lcons_int(int datum, List *list)
  {
  	Assert(IsIntegerList(list));
  
  	if (list == NIL)
  		list = new_list(T_IntList);
  	else
  		new_head_cell(list);
  
  	lfirst_int(list->head) = datum;
  	check_list_invariants(list);
  	return list;
  }
  
  /*
   * Prepend an OID to the list. See lcons()
   */
  List *
  lcons_oid(Oid datum, List *list)
  {
  	Assert(IsOidList(list));
  
  	if (list == NIL)
  		list = new_list(T_OidList);
  	else
  		new_head_cell(list);
  
  	lfirst_oid(list->head) = datum;
  	check_list_invariants(list);
  	return list;
  }
  
  /*
   * Concatenate list2 to the end of list1, and return list1. list1 is
   * destructively changed. Callers should be sure to use the return
   * value as the new pointer to the concatenated list: the 'list1'
   * input pointer may or may not be the same as the returned pointer.
   *
   * The nodes in list2 are merely appended to the end of list1 in-place
   * (i.e. they aren't copied; the two lists will share some of the same
   * storage). Therefore, invoking list_free() on list2 will also
   * invalidate a portion of list1.
   */
  List *
  list_concat(List *list1, List *list2)
  {
  	if (list1 == NIL)
  		return list2;
  	if (list2 == NIL)
  		return list1;
  	if (list1 == list2)
  		elog(ERROR, "cannot list_concat() a list to itself");
  
  	Assert(list1->type == list2->type);
  
  	list1->length += list2->length;
  	list1->tail->next = list2->head;
  	list1->tail = list2->tail;
  
  	check_list_invariants(list1);
  	return list1;
  }
  
  /*
   * Truncate 'list' to contain no more than 'new_size' elements. This
   * modifies the list in-place! Despite this, callers should use the
   * pointer returned by this function to refer to the newly truncated
   * list -- it may or may not be the same as the pointer that was
   * passed.
   *
   * Note that any cells removed by list_truncate() are NOT pfree'd.
   */
  List *
  list_truncate(List *list, int new_size)
  {
  	ListCell   *cell;
  	int			n;
  
  	if (new_size <= 0)
  		return NIL;				/* truncate to zero length */
  
  	/* If asked to effectively extend the list, do nothing */
  	if (new_size >= list_length(list))
  		return list;
  
  	n = 1;
  	foreach(cell, list)
  	{
  		if (n == new_size)
  		{
  			cell->next = NULL;
  			list->tail = cell;
  			list->length = new_size;
  			check_list_invariants(list);
  			return list;
  		}
  		n++;
  	}
  
  	/* keep the compiler quiet; never reached */
  	Assert(false);
  	return list;
  }
  
  /*
   * Locate the n'th cell (counting from 0) of the list.  It is an assertion
   * failure if there is no such cell.
   */
  ListCell *
  list_nth_cell(const List *list, int n)
  {
  	ListCell   *match;
  
  	Assert(list != NIL);
  	Assert(n >= 0);
  	Assert(n < list->length);
  	check_list_invariants(list);
  
  	/* Does the caller actually mean to fetch the tail? */
  	if (n == list->length - 1)
  		return list->tail;
  
  	for (match = list->head; n-- > 0; match = match->next)
  		;
  
  	return match;
  }
  
  /*
   * Return the data value contained in the n'th element of the
   * specified list. (List elements begin at 0.)
   */
  void *
  list_nth(const List *list, int n)
  {
  	Assert(IsPointerList(list));
  	return lfirst(list_nth_cell(list, n));
  }
  
  /*
   * Return the integer value contained in the n'th element of the
   * specified list.
   */
  int
  list_nth_int(const List *list, int n)
  {
  	Assert(IsIntegerList(list));
  	return lfirst_int(list_nth_cell(list, n));
  }
  
  /*
   * Return the OID value contained in the n'th element of the specified
   * list.
   */
  Oid
  list_nth_oid(const List *list, int n)
  {
  	Assert(IsOidList(list));
  	return lfirst_oid(list_nth_cell(list, n));
  }
  
  /*
   * Return true iff 'datum' is a member of the list. Equality is
   * determined via equal(), so callers should ensure that they pass a
   * Node as 'datum'.
   */
  bool
  list_member(const List *list, const void *datum)
  {
  	const ListCell *cell;
  
  	Assert(IsPointerList(list));
  	check_list_invariants(list);
  
  	foreach(cell, list)
  	{
  		if (equal(lfirst(cell), datum))
  			return true;
  	}
  
  	return false;
  }
  
  /*
   * Return true iff 'datum' is a member of the list. Equality is
   * determined by using simple pointer comparison.
   */
  bool
  list_member_ptr(const List *list, const void *datum)
  {
  	const ListCell *cell;
  
  	Assert(IsPointerList(list));
  	check_list_invariants(list);
  
  	foreach(cell, list)
  	{
  		if (lfirst(cell) == datum)
  			return true;
  	}
  
  	return false;
  }
  
  /*
   * Return true iff the integer 'datum' is a member of the list.
   */
  bool
  list_member_int(const List *list, int datum)
  {
  	const ListCell *cell;
  
  	Assert(IsIntegerList(list));
  	check_list_invariants(list);
  
  	foreach(cell, list)
  	{
  		if (lfirst_int(cell) == datum)
  			return true;
  	}
  
  	return false;
  }
  
  /*
   * Return true iff the OID 'datum' is a member of the list.
   */
  bool
  list_member_oid(const List *list, Oid datum)
  {
  	const ListCell *cell;
  
  	Assert(IsOidList(list));
  	check_list_invariants(list);
  
  	foreach(cell, list)
  	{
  		if (lfirst_oid(cell) == datum)
  			return true;
  	}
  
  	return false;
  }
  
  /*
   * Delete 'cell' from 'list'; 'prev' is the previous element to 'cell'
   * in 'list', if any (i.e. prev == NULL iff list->head == cell)
   *
   * The cell is pfree'd, as is the List header if this was the last member.
   */
  List *
  list_delete_cell(List *list, ListCell *cell, ListCell *prev)
  {
  	check_list_invariants(list);
  	Assert(prev != NULL ? lnext(prev) == cell : list_head(list) == cell);
  
  	/*
  	 * If we're about to delete the last node from the list, free the whole
  	 * list instead and return NIL, which is the only valid representation of
  	 * a zero-length list.
  	 */
  	if (list->length == 1)
  	{
  		list_free(list);
  		return NIL;
  	}
  
  	/*
  	 * Otherwise, adjust the necessary list links, deallocate the particular
  	 * node we have just removed, and return the list we were given.
  	 */
  	list->length--;
  
  	if (prev)
  		prev->next = cell->next;
  	else
  		list->head = cell->next;
  
  	if (list->tail == cell)
  		list->tail = prev;
  
  	pfree(cell);
  	return list;
  }
  
  /*
   * Delete the first cell in list that matches datum, if any.
   * Equality is determined via equal().
   */
  List *
  list_delete(List *list, void *datum)
  {
  	ListCell   *cell;
  	ListCell   *prev;
  
  	Assert(IsPointerList(list));
  	check_list_invariants(list);
  
  	prev = NULL;
  	foreach(cell, list)
  	{
  		if (equal(lfirst(cell), datum))
  			return list_delete_cell(list, cell, prev);
  
  		prev = cell;
  	}
  
  	/* Didn't find a match: return the list unmodified */
  	return list;
  }
  
  /* As above, but use simple pointer equality */
  List *
  list_delete_ptr(List *list, void *datum)
  {
  	ListCell   *cell;
  	ListCell   *prev;
  
  	Assert(IsPointerList(list));
  	check_list_invariants(list);
  
  	prev = NULL;
  	foreach(cell, list)
  	{
  		if (lfirst(cell) == datum)
  			return list_delete_cell(list, cell, prev);
  
  		prev = cell;
  	}
  
  	/* Didn't find a match: return the list unmodified */
  	return list;
  }
  
  /* As above, but for integers */
  List *
  list_delete_int(List *list, int datum)
  {
  	ListCell   *cell;
  	ListCell   *prev;
  
  	Assert(IsIntegerList(list));
  	check_list_invariants(list);
  
  	prev = NULL;
  	foreach(cell, list)
  	{
  		if (lfirst_int(cell) == datum)
  			return list_delete_cell(list, cell, prev);
  
  		prev = cell;
  	}
  
  	/* Didn't find a match: return the list unmodified */
  	return list;
  }
  
  /* As above, but for OIDs */
  List *
  list_delete_oid(List *list, Oid datum)
  {
  	ListCell   *cell;
  	ListCell   *prev;
  
  	Assert(IsOidList(list));
  	check_list_invariants(list);
  
  	prev = NULL;
  	foreach(cell, list)
  	{
  		if (lfirst_oid(cell) == datum)
  			return list_delete_cell(list, cell, prev);
  
  		prev = cell;
  	}
  
  	/* Didn't find a match: return the list unmodified */
  	return list;
  }
  
  /*
   * Delete the first element of the list.
   *
   * This is useful to replace the Lisp-y code "list = lnext(list);" in cases
   * where the intent is to alter the list rather than just traverse it.
   * Beware that the removed cell is freed, whereas the lnext() coding leaves
   * the original list head intact if there's another pointer to it.
   */
  List *
  list_delete_first(List *list)
  {
  	check_list_invariants(list);
  
  	if (list == NIL)
  		return NIL;				/* would an error be better? */
  
  	return list_delete_cell(list, list_head(list), NULL);
  }
  
  /*
   * Generate the union of two lists. This is calculated by copying
   * list1 via list_copy(), then adding to it all the members of list2
   * that aren't already in list1.
   *
   * Whether an element is already a member of the list is determined
   * via equal().
   *
   * The returned list is newly-allocated, although the content of the
   * cells is the same (i.e. any pointed-to objects are not copied).
   *
   * NB: this function will NOT remove any duplicates that are present
   * in list1 (so it only performs a "union" if list1 is known unique to
   * start with).  Also, if you are about to write "x = list_union(x, y)"
   * you probably want to use list_concat_unique() instead to avoid wasting
   * the list cells of the old x list.
   *
   * This function could probably be implemented a lot faster if it is a
   * performance bottleneck.
   */
  List *
  list_union(const List *list1, const List *list2)
  {
  	List	   *result;
  	const ListCell *cell;
  
  	Assert(IsPointerList(list1));
  	Assert(IsPointerList(list2));
  
  	result = list_copy(list1);
  	foreach(cell, list2)
  	{
  		if (!list_member(result, lfirst(cell)))
  			result = lappend(result, lfirst(cell));
  	}
  
  	check_list_invariants(result);
  	return result;
  }
  
  /*
   * This variant of list_union() determines duplicates via simple
   * pointer comparison.
   */
  List *
  list_union_ptr(const List *list1, const List *list2)
  {
  	List	   *result;
  	const ListCell *cell;
  
  	Assert(IsPointerList(list1));
  	Assert(IsPointerList(list2));
  
  	result = list_copy(list1);
  	foreach(cell, list2)
  	{
  		if (!list_member_ptr(result, lfirst(cell)))
  			result = lappend(result, lfirst(cell));
  	}
  
  	check_list_invariants(result);
  	return result;
  }
  
  /*
   * This variant of list_union() operates upon lists of integers.
   */
  List *
  list_union_int(const List *list1, const List *list2)
  {
  	List	   *result;
  	const ListCell *cell;
  
  	Assert(IsIntegerList(list1));
  	Assert(IsIntegerList(list2));
  
  	result = list_copy(list1);
  	foreach(cell, list2)
  	{
  		if (!list_member_int(result, lfirst_int(cell)))
  			result = lappend_int(result, lfirst_int(cell));
  	}
  
  	check_list_invariants(result);
  	return result;
  }
  
  /*
   * This variant of list_union() operates upon lists of OIDs.
   */
  List *
  list_union_oid(const List *list1, const List *list2)
  {
  	List	   *result;
  	const ListCell *cell;
  
  	Assert(IsOidList(list1));
  	Assert(IsOidList(list2));
  
  	result = list_copy(list1);
  	foreach(cell, list2)
  	{
  		if (!list_member_oid(result, lfirst_oid(cell)))
  			result = lappend_oid(result, lfirst_oid(cell));
  	}
  
  	check_list_invariants(result);
  	return result;
  }
  
  /*
   * Return a list that contains all the cells that are in both list1 and
   * list2.  The returned list is freshly allocated via palloc(), but the
   * cells themselves point to the same objects as the cells of the
   * input lists.
   *
   * Duplicate entries in list1 will not be suppressed, so it's only a true
   * "intersection" if list1 is known unique beforehand.
   *
   * This variant works on lists of pointers, and determines list
   * membership via equal().  Note that the list1 member will be pointed
   * to in the result.
   */
  List *
  list_intersection(const List *list1, const List *list2)
  {
  	List	   *result;
  	const ListCell *cell;
  
  	if (list1 == NIL || list2 == NIL)
  		return NIL;
  
  	Assert(IsPointerList(list1));
  	Assert(IsPointerList(list2));
  
  	result = NIL;
  	foreach(cell, list1)
  	{
  		if (list_member(list2, lfirst(cell)))
  			result = lappend(result, lfirst(cell));
  	}
  
  	check_list_invariants(result);
  	return result;
  }
  
  /*
   * As list_intersection but operates on lists of integers.
   */
  List *
  list_intersection_int(const List *list1, const List *list2)
  {
  	List	   *result;
  	const ListCell *cell;
  
  	if (list1 == NIL || list2 == NIL)
  		return NIL;
  
  	Assert(IsIntegerList(list1));
  	Assert(IsIntegerList(list2));
  
  	result = NIL;
  	foreach(cell, list1)
  	{
  		if (list_member_int(list2, lfirst_int(cell)))
  			result = lappend_int(result, lfirst_int(cell));
  	}
  
  	check_list_invariants(result);
  	return result;
  }
  
  /*
   * Return a list that contains all the cells in list1 that are not in
   * list2. The returned list is freshly allocated via palloc(), but the
   * cells themselves point to the same objects as the cells of the
   * input lists.
   *
   * This variant works on lists of pointers, and determines list
   * membership via equal()
   */
  List *
  list_difference(const List *list1, const List *list2)
  {
  	const ListCell *cell;
  	List	   *result = NIL;
  
  	Assert(IsPointerList(list1));
  	Assert(IsPointerList(list2));
  
  	if (list2 == NIL)
  		return list_copy(list1);
  
  	foreach(cell, list1)
  	{
  		if (!list_member(list2, lfirst(cell)))
  			result = lappend(result, lfirst(cell));
  	}
  
  	check_list_invariants(result);
  	return result;
  }
  
  /*
   * This variant of list_difference() determines list membership via
   * simple pointer equality.
   */
  List *
  list_difference_ptr(const List *list1, const List *list2)
  {
  	const ListCell *cell;
  	List	   *result = NIL;
  
  	Assert(IsPointerList(list1));
  	Assert(IsPointerList(list2));
  
  	if (list2 == NIL)
  		return list_copy(list1);
  
  	foreach(cell, list1)
  	{
  		if (!list_member_ptr(list2, lfirst(cell)))
  			result = lappend(result, lfirst(cell));
  	}
  
  	check_list_invariants(result);
  	return result;
  }
  
  /*
   * This variant of list_difference() operates upon lists of integers.
   */
  List *
  list_difference_int(const List *list1, const List *list2)
  {
  	const ListCell *cell;
  	List	   *result = NIL;
  
  	Assert(IsIntegerList(list1));
  	Assert(IsIntegerList(list2));
  
  	if (list2 == NIL)
  		return list_copy(list1);
  
  	foreach(cell, list1)
  	{
  		if (!list_member_int(list2, lfirst_int(cell)))
  			result = lappend_int(result, lfirst_int(cell));
  	}
  
  	check_list_invariants(result);
  	return result;
  }
  
  /*
   * This variant of list_difference() operates upon lists of OIDs.
   */
  List *
  list_difference_oid(const List *list1, const List *list2)
  {
  	const ListCell *cell;
  	List	   *result = NIL;
  
  	Assert(IsOidList(list1));
  	Assert(IsOidList(list2));
  
  	if (list2 == NIL)
  		return list_copy(list1);
  
  	foreach(cell, list1)
  	{
  		if (!list_member_oid(list2, lfirst_oid(cell)))
  			result = lappend_oid(result, lfirst_oid(cell));
  	}
  
  	check_list_invariants(result);
  	return result;
  }
  
  /*
   * Append datum to list, but only if it isn't already in the list.
   *
   * Whether an element is already a member of the list is determined
   * via equal().
   */
  List *
  list_append_unique(List *list, void *datum)
  {
  	if (list_member(list, datum))
  		return list;
  	else
  		return lappend(list, datum);
  }
  
  /*
   * This variant of list_append_unique() determines list membership via
   * simple pointer equality.
   */
  List *
  list_append_unique_ptr(List *list, void *datum)
  {
  	if (list_member_ptr(list, datum))
  		return list;
  	else
  		return lappend(list, datum);
  }
  
  /*
   * This variant of list_append_unique() operates upon lists of integers.
   */
  List *
  list_append_unique_int(List *list, int datum)
  {
  	if (list_member_int(list, datum))
  		return list;
  	else
  		return lappend_int(list, datum);
  }
  
  /*
   * This variant of list_append_unique() operates upon lists of OIDs.
   */
  List *
  list_append_unique_oid(List *list, Oid datum)
  {
  	if (list_member_oid(list, datum))
  		return list;
  	else
  		return lappend_oid(list, datum);
  }
  
  /*
   * Append to list1 each member of list2 that isn't already in list1.
   *
   * Whether an element is already a member of the list is determined
   * via equal().
   *
   * This is almost the same functionality as list_union(), but list1 is
  <<<<<<< HEAD
   * modified in-place rather than being copied.  Note also that list2's cells
   * are not inserted in list1, so the analogy to list_concat() isn't perfect.
  =======
   * modified in-place rather than being copied. However, callers of this
   * function may have strict ordering expectations -- i.e. that the relative
   * order of those list2 elements that are not duplicates is preserved. Note
   * also that list2's cells are not inserted in list1, so the analogy to
   * list_concat() isn't perfect.
  >>>>>>> 0c13ee198f0d690765550fc1c694f9191e9785d6
   */
  List *
  list_concat_unique(List *list1, List *list2)
  {
  	ListCell   *cell;
  
  	Assert(IsPointerList(list1));
  	Assert(IsPointerList(list2));
  
  	foreach(cell, list2)
  	{
  		if (!list_member(list1, lfirst(cell)))
  			list1 = lappend(list1, lfirst(cell));
  	}
  
  	check_list_invariants(list1);
  	return list1;
  }
  
  /*
   * This variant of list_concat_unique() determines list membership via
   * simple pointer equality.
   */
  List *
  list_concat_unique_ptr(List *list1, List *list2)
  {
  	ListCell   *cell;
  
  	Assert(IsPointerList(list1));
  	Assert(IsPointerList(list2));
  
  	foreach(cell, list2)
  	{
  		if (!list_member_ptr(list1, lfirst(cell)))
  			list1 = lappend(list1, lfirst(cell));
  	}
  
  	check_list_invariants(list1);
  	return list1;
  }
  
  /*
   * This variant of list_concat_unique() operates upon lists of integers.
   */
  List *
  list_concat_unique_int(List *list1, List *list2)
  {
  	ListCell   *cell;
  
  	Assert(IsIntegerList(list1));
  	Assert(IsIntegerList(list2));
  
  	foreach(cell, list2)
  	{
  		if (!list_member_int(list1, lfirst_int(cell)))
  			list1 = lappend_int(list1, lfirst_int(cell));
  	}
  
  	check_list_invariants(list1);
  	return list1;
  }
  
  /*
   * This variant of list_concat_unique() operates upon lists of OIDs.
   */
  List *
  list_concat_unique_oid(List *list1, List *list2)
  {
  	ListCell   *cell;
  
  	Assert(IsOidList(list1));
  	Assert(IsOidList(list2));
  
  	foreach(cell, list2)
  	{
  		if (!list_member_oid(list1, lfirst_oid(cell)))
  			list1 = lappend_oid(list1, lfirst_oid(cell));
  	}
  
  	check_list_invariants(list1);
  	return list1;
  }
  
  /*
   * Free all storage in a list, and optionally the pointed-to elements
   */
  static void
  list_free_private(List *list, bool deep)
  {
  	ListCell   *cell;
  
  	check_list_invariants(list);
  
  	cell = list_head(list);
  	while (cell != NULL)
  	{
  		ListCell   *tmp = cell;
  
  		cell = lnext(cell);
  		if (deep)
  			pfree(lfirst(tmp));
  		pfree(tmp);
  	}
  
  	if (list)
  		pfree(list);
  }
  
  /*
   * Free all the cells of the list, as well as the list itself. Any
   * objects that are pointed-to by the cells of the list are NOT
   * free'd.
   *
   * On return, the argument to this function has been freed, so the
   * caller would be wise to set it to NIL for safety's sake.
   */
  void
  list_free(List *list)
  {
  	list_free_private(list, false);
  }
  
  /*
   * Free all the cells of the list, the list itself, and all the
   * objects pointed-to by the cells of the list (each element in the
   * list must contain a pointer to a palloc()'d region of memory!)
   *
   * On return, the argument to this function has been freed, so the
   * caller would be wise to set it to NIL for safety's sake.
   */
  void
  list_free_deep(List *list)
  {
  	/*
  	 * A "deep" free operation only makes sense on a list of pointers.
  	 */
  	Assert(IsPointerList(list));
  	list_free_private(list, true);
  }
  
  /*
   * Return a shallow copy of the specified list.
   */
  List *
  list_copy(const List *oldlist)
  {
  	List	   *newlist;
  	ListCell   *newlist_prev;
  	ListCell   *oldlist_cur;
  
  	if (oldlist == NIL)
  		return NIL;
  
  	newlist = new_list(oldlist->type);
  	newlist->length = oldlist->length;
  
  	/*
  	 * Copy over the data in the first cell; new_list() has already allocated
  	 * the head cell itself
  	 */
  	newlist->head->data = oldlist->head->data;
  
  	newlist_prev = newlist->head;
  	oldlist_cur = oldlist->head->next;
  	while (oldlist_cur)
  	{
  		ListCell   *newlist_cur;
  
  		newlist_cur = (ListCell *) palloc(sizeof(*newlist_cur));
  		newlist_cur->data = oldlist_cur->data;
  		newlist_prev->next = newlist_cur;
  
  		newlist_prev = newlist_cur;
  		oldlist_cur = oldlist_cur->next;
  	}
  
  	newlist_prev->next = NULL;
  	newlist->tail = newlist_prev;
  
  	check_list_invariants(newlist);
  	return newlist;
  }
  
  /*
   * Return a shallow copy of the specified list, without the first N elements.
   */
  List *
  list_copy_tail(const List *oldlist, int nskip)
  {
  	List	   *newlist;
  	ListCell   *newlist_prev;
  	ListCell   *oldlist_cur;
  
  	if (nskip < 0)
  		nskip = 0;				/* would it be better to elog? */
  
  	if (oldlist == NIL || nskip >= oldlist->length)
  		return NIL;
  
  	newlist = new_list(oldlist->type);
  	newlist->length = oldlist->length - nskip;
  
  	/*
  	 * Skip over the unwanted elements.
  	 */
  	oldlist_cur = oldlist->head;
  	while (nskip-- > 0)
  		oldlist_cur = oldlist_cur->next;
  
  	/*
  	 * Copy over the data in the first remaining cell; new_list() has already
  	 * allocated the head cell itself
  	 */
  	newlist->head->data = oldlist_cur->data;
  
  	newlist_prev = newlist->head;
  	oldlist_cur = oldlist_cur->next;
  	while (oldlist_cur)
  	{
  		ListCell   *newlist_cur;
  
  		newlist_cur = (ListCell *) palloc(sizeof(*newlist_cur));
  		newlist_cur->data = oldlist_cur->data;
  		newlist_prev->next = newlist_cur;
  
  		newlist_prev = newlist_cur;
  		oldlist_cur = oldlist_cur->next;
  	}
  
  	newlist_prev->next = NULL;
  	newlist->tail = newlist_prev;
  
  	check_list_invariants(newlist);
  	return newlist;
  }
  
  /*
  <<<<<<< HEAD
  =======
   * Sort a list as though by qsort.
   *
   * A new list is built and returned.  Like list_copy, this doesn't make
   * fresh copies of any pointed-to data.
   *
   * The comparator function receives arguments of type ListCell **.
   */
  List *
  list_qsort(const List *list, list_qsort_comparator cmp)
  {
  	int			len = list_length(list);
  	ListCell  **list_arr;
  	List	   *newlist;
  	ListCell   *newlist_prev;
  	ListCell   *cell;
  	int			i;
  
  	/* Empty list is easy */
  	if (len == 0)
  		return NIL;
  
  	/* Flatten list cells into an array, so we can use qsort */
  	list_arr = (ListCell **) palloc(sizeof(ListCell *) * len);
  	i = 0;
  	foreach(cell, list)
  		list_arr[i++] = cell;
  
  	qsort(list_arr, len, sizeof(ListCell *), cmp);
  
  	/* Construct new list (this code is much like list_copy) */
  	newlist = new_list(list->type);
  	newlist->length = len;
  
  	/*
  	 * Copy over the data in the first cell; new_list() has already allocated
  	 * the head cell itself
  	 */
  	newlist->head->data = list_arr[0]->data;
  
  	newlist_prev = newlist->head;
  	for (i = 1; i < len; i++)
  	{
  		ListCell   *newlist_cur;
  
  		newlist_cur = (ListCell *) palloc(sizeof(*newlist_cur));
  		newlist_cur->data = list_arr[i]->data;
  		newlist_prev->next = newlist_cur;
  
  		newlist_prev = newlist_cur;
  	}
  
  	newlist_prev->next = NULL;
  	newlist->tail = newlist_prev;
  
  	/* Might as well free the workspace array */
  	pfree(list_arr);
  
  	check_list_invariants(newlist);
  	return newlist;
  }
  
  /*
  >>>>>>> 0c13ee198f0d690765550fc1c694f9191e9785d6
   * Temporary compatibility functions
   *
   * In order to avoid warnings for these function definitions, we need
   * to include a prototype here as well as in pg_list.h. That's because
   * we don't enable list API compatibility in list.c, so we
   * don't see the prototypes for these functions.
   */
  
  /*
   * Given a list, return its length. This is merely defined for the
   * sake of backward compatibility: we can't afford to define a macro
   * called "length", so it must be a function. New code should use the
   * list_length() macro in order to avoid the overhead of a function
   * call.
   */
  int			length(const List *list);
  
  int
  length(const List *list)
  {
  	return list_length(list);
  }
  