/*
** Copyright (C) 1998-1999 The University of Melbourne.
** This file may only be copied under the terms of the GNU Library General
** Public License - see the file COPYING.LIB in the Mercury distribution.
*/

/*
** mercury_macros.h defines macros that are useful in more than one
** module of the Mercury runtime system.
*/

#ifndef MERCURY_ARRAY_MACROS_H
#define MERCURY_ARRAY_MACROS_H

#include	"mercury_misc.h"	/* for MR_memcpy */

/*
** This macro defines a safe way to perform assignment between
** array elements that are structures. The obvious way can cause
** gcc 2.7.2.3 to abort on x86 processors with the message 
** "fixed or forbidden register was spilled."
*/

#ifdef	MR_CANNOT_USE_STRUCTURE_ASSIGNMENT

  #define MR_copy_array_element(array, to_index, from_index)		\
	do {								\
		MR_memcpy((void *) &array[to_index],			\
			(const void *) &array[from_index],		\
			sizeof(array[to_index]));			\
	} while(0)

#else

  #define MR_copy_array_element(array, to_index, from_index)		\
	do {								\
		array[to_index] = array[from_index];			\
	} while(0)

#endif /* ! MR_CANNOT_USE_STRUCTURE_ASSIGNMENT */

/*
** The MR_ensure_room_for_next macro works with a group of three variables
** that follow the pattern
**
**	Item	widgets = NULL;
**	int	widget_max = 0;
**	int	widget_next = 0;
**
** where widgets is a pointer to a malloc'd array of items, widget_max
** gives the number of elements in the array, and widget_next is the
** index of the first free slot in the widgets array. Widget_max is
** zero if and only if widgets is NULL.
**
** MR_ensure_room_for_next(widget, Item, INIT_SIZE) checks whether
** there is enough room in the widgets array to add a new item.
** If not, doubles the size of the existing widgets array, or
** allocates an array of INIT_SIZE items if the widgets array
** has not been initialized before.
*/

#define	MR_ensure_room_for_next(base, type, init)	  		    \
	do {								    \
		if (base##_next >= base##_max) {			    \
			if (base##_max == 0) {				    \
				base##_max = init;			    \
				base##s = checked_malloc(		    \
						base##_max * sizeof(type)); \
			} else {					    \
				base##_max *= 2;			    \
				base##s = checked_realloc(base##s, 	    \
						base##_max * sizeof(type)); \
			}						    \
		}							    \
	} while(0)

/*
** MR_ensure_big_enough makes the same assumptions as MR_ensure_room_for_next,
** and operates almost the same way. The exception is that it does not assume
** that the array grows one item at a time; instead it ensures that the array
** is big enough to contain the element at index `slot'. Since with this regime
** there is no notion of the "next" slot, this macro does not access, nor does
** it require the existence of, base##_next.
*/

#define	MR_ensure_big_enough(slot, base, type, init)	  		    \
	do {								    \
		if (slot >= base##_max) {				    \
			if (base##_max == 0) {				    \
				base##_max = max(init, slot + 1);	    \
				base##s = checked_malloc(		    \
						base##_max * sizeof(type)); \
			} else {					    \
				base##_max = max(base##_max * 2, slot + 1); \
				base##s = checked_realloc(base##s, 	    \
						base##_max * sizeof(type)); \
			}						    \
		}							    \
	} while(0)

/*
** MR_ensure_big_enough2 works like MR_ensure_big_enough, except that
** it resizes two arrays at once. These two arrays are named base##s1 and
** base##s2, and since they are always the same size, they share the
** base##_max variable.
*/

#define	MR_ensure_big_enough2(slot, base, s1, s2, type, init)  		    \
	do {								    \
		if (slot >= base##_max) {				    \
			if (base##_max == 0) {				    \
				base##_max = max(init, slot + 1);	    \
				base##s1 = checked_malloc(		    \
						base##_max * sizeof(type)); \
				base##s2 = checked_malloc(		    \
						base##_max * sizeof(type)); \
			} else {					    \
				base##_max = max(base##_max * 2, slot + 1); \
				base##s1 = checked_realloc(base##s1, 	    \
						base##_max * sizeof(type)); \
				base##s2 = checked_realloc(base##s2, 	    \
						base##_max * sizeof(type)); \
			}						    \
		}							    \
	} while(0)

/*
** MR_bsearch(int next, int& element, bool& found, COMPARE)
**
** Given a sorted array, this macro performs a binary search.
** If the search is successful, MR_bsearch sets the `found' parameter
** to TRUE and the `element' parameter to the index of the desired item.
** If the search is unsuccessful, MR_bsearch sets `found' to FALSE;
** `element' will be clobbered.
**
** The number of the elements in the array is given by the `next' parameter.
** The `COMPARE' parameter should be an expression of type int which compares
** the value at the index specified by the current value of `element'
** with the desired value, and returns <0, 0, or >0 according to whether 
** it is less than, equal to, or greater than the desired value.
**
** The name of the array to be searched is not explicitly a parameter;
** its identity is encoded in the boolean expression of the `COMPARE'
** parameter.
*/

#define MR_bsearch(next, element, found, COMPARE)			\
	do {								\
		int	lo;						\
		int	hi;						\
		int	diff;						\
									\
		/*							\
		** We initialize `element' here only to avoid gcc	\
		** warnings about possibly accessing an uninitialized	\
		** variable in code using MR_bsearch().			\
		*/							\
		(element) = 0;						\
		lo = 0;							\
		hi = (next) - 1;					\
		(found) = FALSE;					\
		while (lo <= hi) {					\
			(element) = (lo + hi) / 2;			\
			diff = (COMPARE);				\
			if (diff == 0) {				\
				(found) = TRUE;				\
				break;					\
			} else if (diff < 0) {				\
				lo = (element) + 1;			\
			} else {					\
				hi = (element) - 1;			\
			}						\
		}							\
	} while(0)

/*
** MR_prepare_insert_into_sorted(array[], int& next, int& element, COMPARE)
**
** Given a sorted array `items', this prepares for the insertion of a new
** item into the array at the proper point. It find the index at which
** the new item should be inserted, and moves all items at and above that
** index one position to the right to make room for the new item.
**
** The `next' parameter holds the number of elements in the array;
** it is incremented by this macro. The macro returns the index of the slot
** at which the new item should be inserted in the `element' parameter.
** The `COMPARE' parameter should be an expression of type int which compares
** the item at the index specified by the current value of `element' with
** the item being inserted, and returns <0, 0, or >0 according to whether
** it is less than, equal to, or greater than the item being inserted.
*/

#define MR_prepare_insert_into_sorted(items, next, element, COMPARE)	\
	do {								\
		(element) = (next) - 1;					\
		while ((element) >= 0 && (COMPARE) > 0) {		\
			MR_copy_array_element(items, element + 1,	\
				element);				\
			(element) -= 1;					\
		}							\
		(element) += 1;						\
		(next) += 1;						\
	} while(0)

#endif /* MERCURY_ARRAY_MACROS_H */