/*-------------------------------------------------------------------------
 *
 * fstack.c--
 *	  Fixed format stack definitions.
 *
 * Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $Header: /usr/local/cvsroot/pgsql/src/backend/lib/fstack.c,v 1.6 1997/09/08 02:22:57 momjian Exp $
 *
 *-------------------------------------------------------------------------
 */
#include <postgres.h>

#include <lib/fstack.h>

/*
 * Internal function definitions
 */

/*
 * FixedItemIsValid --
 *		True iff item is valid.
 */
#define FixedItemIsValid(item)	PointerIsValid(item)

/*
 * FixedStackGetItemBase --
 *		Returns base of enclosing structure.
 */
#define FixedStackGetItemBase(stack, item) \
		((Pointer)((char *)(item) - (stack)->offset))

/*
 * FixedStackGetItem --
 *		Returns item of given pointer to enclosing structure.
 */
#define FixedStackGetItem(stack, pointer) \
		((FixedItem)((char *)(pointer) + (stack)->offset))

#define FixedStackIsValid(stack) ((bool)PointerIsValid(stack))

/*
 * External functions
 */

void
FixedStackInit(FixedStack stack, Offset offset)
{
	AssertArg(PointerIsValid(stack));

	stack->top = NULL;
	stack->offset = offset;
}

Pointer
FixedStackPop(FixedStack stack)
{
	Pointer		pointer;

	AssertArg(FixedStackIsValid(stack));

	if (!PointerIsValid(stack->top))
	{
		return (NULL);
	}

	pointer = FixedStackGetItemBase(stack, stack->top);
	stack->top = stack->top->next;

	return (pointer);
}

void
FixedStackPush(FixedStack stack, Pointer pointer)
{
	FixedItem	item = FixedStackGetItem(stack, pointer);

	AssertArg(FixedStackIsValid(stack));
	AssertArg(PointerIsValid(pointer));

	item->next = stack->top;
	stack->top = item;
}

#ifndef NO_ASSERT_CHECKING
/*
 * FixedStackContains --
 *		True iff ordered stack contains given element.
 *
 * Note:
 *		This is inefficient.  It is intended for debugging use only.
 *
 * Exceptions:
 *		BadArg if stack is invalid.
 *		BadArg if pointer is invalid.
 */
static bool
FixedStackContains(FixedStack stack, Pointer pointer)
{
	FixedItem	next;
	FixedItem	item;

	AssertArg(FixedStackIsValid(stack));
	AssertArg(PointerIsValid(pointer));

	item = FixedStackGetItem(stack, pointer);

	for (next = stack->top; FixedItemIsValid(next); next = next->next)
	{
		if (next == item)
		{
			return (true);
		}
	}
	return (false);
}

#endif

Pointer
FixedStackGetTop(FixedStack stack)
{
	AssertArg(FixedStackIsValid(stack));

	if (!PointerIsValid(stack->top))
	{
		return (NULL);
	}

	return (FixedStackGetItemBase(stack, stack->top));
}

Pointer
FixedStackGetNext(FixedStack stack, Pointer pointer)
{
	FixedItem	item;

	/* AssertArg(FixedStackIsValid(stack)); */
	/* AssertArg(PointerIsValid(pointer)); */
	AssertArg(FixedStackContains(stack, pointer));

	item = FixedStackGetItem(stack, pointer)->next;

	if (!PointerIsValid(item))
	{
		return (NULL);
	}

	return (FixedStackGetItemBase(stack, item));
}