/**
 *  memory.h
 *
 *  Grendel: a compiling Beowulf reimplementation.
 *
 *  The memory management subsystem.
 *
 *  (c) 2026 Simon Brooke <simon@journeyman.cc>
 *  Licensed under GPL version 2.0, or, at your option, any later version.
 */

#ifndef __grendel_memory_h
#define __grendel_memory_h

#include <stdint.h>

/* Tags for 32 bit objects, with 3 bits of tag an one mark bit */

/**
 * This pointer object is an actual pointer -- an offset into consspace.
 */
#define OFFSETTV 		0
/**
 * This pointer object is actually a 28 bit integer value.
 */
#define INTEGERTV 		1
/*
 * Values 2..6 inclusive reserved further data types, including maybe
 * implementing reals later.
 */

/**
 * This is not actually a pointer at all but the first word of a cell.
 */
#define CELLTV			7

/**
 * Half of a cons cell. The mark bit is first, so that the ptag can be
 * considered as part of the CTAG.
 */
struct pointer {
	/* mark bit for mark and sweep garbage collector. Yes, this is normally
	 * thought of as part of the cell, but bear with me. */
	unsigned int mark : 1;
	/* pointer tag, interpretations as above */
	unsigned int ptag : 3;
	/* the actual payload of the pointer object */
	union {
		unsigned int offset : 28;
		int value : 28;
	} payload;
};

struct cons_payload {
	struct pointer pointers[2];
};

struct symbol_payload {
	/* this is the same mark bit as the one in the `address` pointer of the
	 * cons_payload. */
	unsigned int mark : 1;
	unsigned int tag : 7;
	char symbol[7];
};

/* Tags for 64 bit objects. Note that, as the 64 bit object may be made up
 * of two 32 bit objects (pointers*, the 64 bit tag is stored in bits 4..7
 * inclusive. The first three bits are the first three bits of a 32 bit object,
 * and thus for 64bit objects will always b 111.*/

/* this 64 bit object is a cons cell */
#define CONSTV 7

/* this 64 bit object is a seven character atom */
#define ATOMTV 8

/* There are potentially another 119 types of object we could store in a 64
 * bit object, but I can't think of any we need just now. */

struct cell {
	union {
		struct cons_payload cons;
		struct symbol_payload symbol;
	} payload;
};

#define CONSSPACESIZE 65536

/**
 * The entire array of cells available to the system.
 */
struct cell consspace[CONSSPACESIZE];

#endif