/* fastmem.c - Memory related functions (fast version without virtual memory)
 *		Copyright (c) 1995-1997 Stefan Jokisch
 *
 * This file is part of Frotz.
 *
 * Frotz is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * Frotz is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
 */

/*
 * New undo mechanism added by Jim Dunleavy <jim.dunleavy@erha.ie>
 */

/*
 * Glk and Blorb support added by Tor Andersson.
 */

#include "frotz.h"

#include "glk.h"
#include "glkio.h"
#include "glkstart.h"
#include "gi_blorb.h"

extern void seed_random (int);
extern void restart_screen (void);
extern void refresh_text_style (void);
extern void call (zword, int, zword *, int);
extern void split_window (zword);
extern void script_open (void);
extern void script_close (void);

extern zword save_quetzal (FILE *, FILE *, int);
extern zword restore_quetzal (FILE *, FILE *, int);

extern void erase_window (zword);

extern void (*op0_opcodes[]) (void);
extern void (*op1_opcodes[]) (void);
extern void (*op2_opcodes[]) (void);
extern void (*var_opcodes[]) (void);

zbyte *zmp = NULL;
zbyte *pcp = NULL;

static FILE *story_fp = NULL;
static size_t blorb_ofs = 0;
static size_t blorb_len = 0;

/*
 * Data for the undo mechanism.
 * This undo mechanism is based on the scheme used in Evin Robertson's
 * Nitfol interpreter.
 * Undo blocks are stored as differences between states.
 */

typedef struct undo_struct undo_t;
struct undo_struct {
		undo_t *next;
		undo_t *prev;
		long pc;
		long diff_size;
		zword frame_count;
		zword stack_size;
		zword frame_offset;
		/* undo diff and stack data follow */
};

static undo_t *first_undo = NULL, *last_undo = NULL, *curr_undo = NULL;
static zbyte *undo_mem = NULL, *prev_zmp, *undo_diff;

static int undo_count = 0;

/*
 * get_header_extension
 *
 * Read a value from the header extension (former mouse table).
 *
 */

zword get_header_extension (int entry)
{
		zword addr;
		zword val;

		if (h_extension_table == 0 || entry > hx_table_size)
				return 0;

		addr = h_extension_table + 2 * entry;
		LOW_WORD (addr, val);

		return val;

}/* get_header_extension */

/*
 * set_header_extension
 *
 * Set an entry in the header extension (former mouse table).
 *
 */

void set_header_extension (int entry, zword val)
{
		zword addr;

		if (h_extension_table == 0 || entry > hx_table_size)
				return;

		addr = h_extension_table + 2 * entry;
		SET_WORD (addr, val);

}/* set_header_extension */

/*
 * restart_header
 *
 * Set all header fields which hold information about the interpreter.
 *
 */

void restart_header (void)
{
		zword screen_x_size;
		zword screen_y_size;
		zbyte font_x_size;
		zbyte font_y_size;

		int i;

		SET_BYTE (H_CONFIG, h_config);
		SET_WORD (H_FLAGS, h_flags);

		if (h_version >= V4) {
				SET_BYTE (H_INTERPRETER_NUMBER, h_interpreter_number);
				SET_BYTE (H_INTERPRETER_VERSION, h_interpreter_version);
				SET_BYTE (H_SCREEN_ROWS, h_screen_rows);
				SET_BYTE (H_SCREEN_COLS, h_screen_cols);
		}

		/* It's less trouble to use font size 1x1 for V5 games, especially
		   because of a bug in the unreleased German version of "Zork 1" */

		if (h_version != V6) {
				screen_x_size = (zword) h_screen_cols;
				screen_y_size = (zword) h_screen_rows;
				font_x_size = 1;
				font_y_size = 1;
		} else {
				screen_x_size = h_screen_width;
				screen_y_size = h_screen_height;
				font_x_size = h_font_width;
				font_y_size = h_font_height;
		}

		if (h_version >= V5) {
				SET_WORD (H_SCREEN_WIDTH, screen_x_size);
				SET_WORD (H_SCREEN_HEIGHT, screen_y_size);
				SET_BYTE (H_FONT_HEIGHT, font_y_size);
				SET_BYTE (H_FONT_WIDTH, font_x_size);
				SET_BYTE (H_DEFAULT_BACKGROUND, h_default_background);
				SET_BYTE (H_DEFAULT_FOREGROUND, h_default_foreground);
		}

		if (h_version == V6)
				for (i = 0; i < 8; i++)
						storeb ((zword) (H_USER_NAME + i), h_user_name[i]);

		SET_BYTE (H_STANDARD_HIGH, h_standard_high);
		SET_BYTE (H_STANDARD_LOW, h_standard_low);

}/* restart_header */

/*
 * init_memory
 *
 * Allocate memory and load the story file.
 *
 */

void init_memory (void *filep)
{
		long size;
		zword addr;
		unsigned n;
		int i, j;
		strid_t file = filep;

		static struct {
				enum story story_id;
				zword release;
				zbyte serial[6];
		} records[] = {
				{       SHERLOCK,  21, "871214" },
				{       SHERLOCK,  26, "880127" },
				{    BEYOND_ZORK,  47, "870915" },
				{    BEYOND_ZORK,  49, "870917" },
				{    BEYOND_ZORK,  51, "870923" },
				{    BEYOND_ZORK,  57, "871221" },
				{      ZORK_ZERO, 296, "881019" },
				{      ZORK_ZERO, 366, "890323" },
				{      ZORK_ZERO, 383, "890602" },
				{      ZORK_ZERO, 393, "890714" },
				{         SHOGUN, 292, "890314" },
				{         SHOGUN, 295, "890321" },
				{         SHOGUN, 311, "890510" },
				{         SHOGUN, 322, "890706" },
				{         ARTHUR,  54, "890606" },
				{         ARTHUR,  63, "890622" },
				{         ARTHUR,  74, "890714" },
				{        JOURNEY,  26, "890316" },
				{        JOURNEY,  30, "890322" },
				{        JOURNEY,  77, "890616" },
				{        JOURNEY,  83, "890706" },
				{ LURKING_HORROR, 203, "870506" },
				{ LURKING_HORROR, 219, "870912" },
				{ LURKING_HORROR, 221, "870918" },
				{        UNKNOWN,   0, "------" }
		};

		/* Open story file */
		{
				giblorb_map_t *map;
				giblorb_result_t res;
				char magic[4] = "XXXX";

				fread(magic, 1, 4, file);

				if (!memcmp(magic, "FORM", 4))
				{
						if (giblorb_set_resource_map(file))
								os_fatal("This Blorb file seems to be invalid.");

						map = giblorb_get_resource_map();

						if (giblorb_load_resource(map, giblorb_method_FilePos,
												&res, giblorb_ID_Exec, 0))
								os_fatal("This Blorb file does not contain an executable chunk.");
						if (res.chunktype != giblorb_make_id('Z','C','O','D'))
								os_fatal("This Blorb file contains an executable chunk, but it is not a Z-code file.");

						story_fp = file;
						blorb_ofs = res.data.startpos;
						blorb_len = res.length;
				}
				else
				{
						story_fp = file;		
						blorb_ofs = 0;
						fseek(story_fp, 0, SEEK_END);
						blorb_len = ftell(story_fp);
				}

		}

		if (blorb_len < 64)
				os_fatal("This file is too small to be a Z-code file.");

		/* Allocate memory for story header */

		if ((zmp = (zbyte *) malloc (64)) == NULL)
				os_fatal ("Out of memory");

		/* Load header into memory */

		fseek(story_fp, blorb_ofs, 0);

		if (fread (zmp, 1, 64, story_fp) != 64)
				os_fatal ("Story file read error");

		/* Copy header fields to global variables */

		LOW_BYTE (H_VERSION, h_version);

		if (h_version < V1 || h_version > V8)
				os_fatal ("Unknown Z-code version");

		if (h_version == V6)
				os_fatal ("Cannot play Z-code version 6");

		LOW_BYTE (H_CONFIG, h_config);

		if (h_version == V3 && (h_config & CONFIG_BYTE_SWAPPED))
				os_fatal ("Byte swapped story file");

		LOW_WORD (H_RELEASE, h_release);
		LOW_WORD (H_RESIDENT_SIZE, h_resident_size);
		LOW_WORD (H_START_PC, h_start_pc);
		LOW_WORD (H_DICTIONARY, h_dictionary);
		LOW_WORD (H_OBJECTS, h_objects);
		LOW_WORD (H_GLOBALS, h_globals);
		LOW_WORD (H_DYNAMIC_SIZE, h_dynamic_size);
		LOW_WORD (H_FLAGS, h_flags);

		for (i = 0, addr = H_SERIAL; i < 6; i++, addr++)
				LOW_BYTE (addr, h_serial[i]);

		/* Auto-detect buggy story files that need special fixes */

		story_id = UNKNOWN;

		for (i = 0; records[i].story_id != UNKNOWN; i++) {

				if (h_release == records[i].release) {

						for (j = 0; j < 6; j++)
								if (h_serial[j] != records[i].serial[j])
										goto no_match;

						story_id = records[i].story_id;

				}

no_match: ; /* null statement */

		}

		LOW_WORD (H_ABBREVIATIONS, h_abbreviations);
		LOW_WORD (H_FILE_SIZE, h_file_size);

		/* Calculate story file size in bytes */

		if (h_file_size != 0) {

				story_size = (long) 2 * h_file_size;

				if (h_version >= V4)
						story_size *= 2;
				if (h_version >= V6)
						story_size *= 2;

		} else {				/* some old games lack the file size entry */

				story_size = blorb_len;
		}

		LOW_WORD (H_CHECKSUM, h_checksum);
		LOW_WORD (H_ALPHABET, h_alphabet);
		LOW_WORD (H_FUNCTIONS_OFFSET, h_functions_offset);
		LOW_WORD (H_STRINGS_OFFSET, h_strings_offset);
		LOW_WORD (H_TERMINATING_KEYS, h_terminating_keys);
		LOW_WORD (H_EXTENSION_TABLE, h_extension_table);

		/* Zork Zero Macintosh doesn't have the graphics flag set */

		if (story_id == ZORK_ZERO && h_release == 296)
				h_flags |= GRAPHICS_FLAG;

		/* Adjust opcode tables */

		if (h_version <= V4) {
				op0_opcodes[0x09] = z_pop;
				op1_opcodes[0x0f] = z_not;
		} else {
				op0_opcodes[0x09] = z_catch;
				op1_opcodes[0x0f] = z_call_n;
		}

		/* Allocate memory for story data */

		if ((zmp = (zbyte *) realloc (zmp, story_size)) == NULL)
				os_fatal ("Out of memory");

		/* Load story file in chunks of 32KB */

		n = 0x8000;

		for (size = 64; size < story_size; size += n) {

				if (story_size - size < 0x8000)
						n = (unsigned) (story_size - size);

				SET_PC (size);

				if (fread (pcp, 1, n, story_fp) != n)
						os_fatal ("Story file read error");

		}

		/* Read header extension table */

		hx_table_size = get_header_extension (HX_TABLE_SIZE);
		hx_unicode_table = get_header_extension (HX_UNICODE_TABLE);

}/* init_memory */

/*
 * init_undo
 *
 * Allocate memory for multiple undo. It is important not to occupy
 * all the memory available, since the IO interface may need memory
 * during the game, e.g. for loading sounds or pictures.
 *
 */

void init_undo (void)
{
		void *reserved;

		reserved = NULL;		/* makes compilers shut up */

		if (reserve_mem != 0) {
				if ((reserved = malloc (reserve_mem)) == NULL)
						return;
		}

		/* Allocate h_dynamic_size bytes for previous dynamic zmp state
		   + 1.5 h_dynamic_size for Quetzal diff + 2. */
		undo_mem = malloc ((h_dynamic_size * 5) / 2 + 2);
		if (undo_mem != NULL) {
				prev_zmp = undo_mem;
				undo_diff = undo_mem + h_dynamic_size;
				memcpy (prev_zmp, zmp, h_dynamic_size);
		} else
				f_setup.undo_slots = 0;

		if (reserve_mem != 0)
				free (reserved);

}/* init_undo */

/*
 * free_undo
 *
 * Free count undo blocks from the beginning of the undo list.
 *
 */

static void free_undo (int count)
{
		undo_t *p;

		if (count > undo_count)
				count = undo_count;
		while (count--) {
				p = first_undo;
				if (curr_undo == first_undo)
						curr_undo = curr_undo->next;
				first_undo = first_undo->next;
				free (p);
				undo_count--;
		}
		if (first_undo)
				first_undo->prev = NULL;
		else
				last_undo = NULL;
}/* free_undo */

/*
 * reset_memory
 *
 * Close the story file and deallocate memory.
 *
 */

void reset_memory (void)
{
		if (story_fp) 
				fclose (story_fp);
		story_fp = NULL;
		blorb_ofs = 0;
		blorb_len = 0;

		if (undo_mem) {
				free_undo (undo_count);
				free (undo_mem);
		}

		undo_mem = NULL;
		undo_count = 0;

		if (zmp)
				free (zmp);
		zmp = NULL;
}/* reset_memory */

/*
 * storeb
 *
 * Write a byte value to the dynamic Z-machine memory.
 *
 */

void storeb (zword addr, zbyte value)
{

		if (addr >= h_dynamic_size)
				runtime_error (ERR_STORE_RANGE);

		if (addr == H_FLAGS + 1) {		/* flags register is modified */

				h_flags &= ~(SCRIPTING_FLAG | FIXED_FONT_FLAG);
				h_flags |= value & (SCRIPTING_FLAG | FIXED_FONT_FLAG);

				if (value & SCRIPTING_FLAG) {
						if (!ostream_script)
								script_open ();
				} else {
						if (ostream_script)
								script_close ();
				}

				/* TOR - glkified / refresh_text_style (); */

		}

		SET_BYTE (addr, value);

}/* storeb */

/*
 * storew
 *
 * Write a word value to the dynamic Z-machine memory.
 *
 */

void storew (zword addr, zword value)
{

		storeb ((zword) (addr + 0), hi (value));
		storeb ((zword) (addr + 1), lo (value));

}/* storew */

/*
 * z_restart, re-load dynamic area, clear the stack and set the PC.
 *
 * 		no zargs used
 *
 */

void z_restart (void)
{
		static bool first_restart = TRUE;

		flush_buffer ();

		os_restart_game (RESTART_BEGIN);

		seed_random (0);

		if (!first_restart) {

				fseek (story_fp, blorb_ofs, SEEK_SET);

				if (fread (zmp, 1, h_dynamic_size, story_fp) != h_dynamic_size)
						os_fatal ("Story file read error");

		} else first_restart = FALSE;

		restart_header ();
		restart_screen ();

		sp = fp = stack + STACK_SIZE;
		frame_count = 0;

		if (h_version != V6) {

				long pc = (long) h_start_pc;
				SET_PC (pc);

		} else call (h_start_pc, 0, NULL, 0);

		os_restart_game (RESTART_END);

}/* z_restart */

/*
 * z_restore, restore [a part of] a Z-machine state from disk
 *
 *		zargs[0] = address of area to restore (optional)
 *		zargs[1] = number of bytes to restore
 *		zargs[2] = address of suggested file name
 *
 */

void z_restore (void)
{
		FILE *gfp;

		zword success = 0;

		if (zargc != 0) {

				/* Get the file name */

				/* Open auxilary file */

				if ((gfp = frotzopenprompt(FILE_LOAD_AUX)) == NULL)
						goto finished;

				/* Load auxilary file */

				success = fread (zmp + zargs[0], 1, zargs[1], gfp);

				/* Close auxilary file */

				fclose (gfp);

		} else {

				long pc;
				zword release;
				zword addr;
				int i;

				/* Open game file */

				if ((gfp = frotzopenprompt(FILE_RESTORE)) == NULL)
						goto finished;

				if (f_setup.save_quetzal) {
						success = restore_quetzal (gfp, story_fp, blorb_ofs);

				} else {
						/* Load game file */

						release = (unsigned) fgetc (gfp) << 8;
						release |= fgetc (gfp);

						(void) fgetc (gfp);
						(void) fgetc (gfp);

						/* Check the release number */

						if (release == h_release) {

								pc = (long) fgetc (gfp) << 16;
								pc |= (unsigned) fgetc (gfp) << 8;
								pc |= fgetc (gfp);

								SET_PC (pc);

								sp = stack + (fgetc (gfp) << 8);
								sp += fgetc (gfp);
								fp = stack + (fgetc (gfp) << 8);
								fp += fgetc (gfp);

								for (i = (int) (sp - stack); i < STACK_SIZE; i++) {
										stack[i] = (unsigned) fgetc (gfp) << 8;
										stack[i] |= fgetc (gfp);
								}

								fseek (story_fp, blorb_ofs, SEEK_SET);

								for (addr = 0; addr < h_dynamic_size; addr++) {
										int skip = fgetc (gfp);
										for (i = 0; i < skip; i++)
												zmp[addr++] = fgetc (story_fp);
										zmp[addr] = fgetc (gfp);
										(void) fgetc (story_fp);
								}

								/* Check for errors */

								if (ferror (gfp) || ferror (story_fp) || addr != h_dynamic_size)
										success = -1;
								else

										/* Success */

										success = 2;

						} else print_string ("Invalid save file\n");
				}

				if ((short) success >= 0) {

						/* Close game file */

						fclose (gfp);

						if ((short) success > 0) {
								zbyte old_screen_rows;
								zbyte old_screen_cols;

								/* In V3, reset the upper window. */
								if (h_version == V3)
										split_window (0);

								LOW_BYTE (H_SCREEN_ROWS, old_screen_rows);
								LOW_BYTE (H_SCREEN_COLS, old_screen_cols);

								/* Reload cached header fields. */
								restart_header ();

								/*
								 * Since QUETZAL files may be saved on many different machines,
								 * the screen sizes may vary a lot. Erasing the status window
								 * seems to cover up most of the resulting badness.
								 */
								if (h_version > V3 && h_version != V6
												&& (h_screen_rows != old_screen_rows
														|| h_screen_cols != old_screen_cols))
										erase_window (1);
						}
				} else
						os_fatal ("Error reading save file");
		}

finished:

		if (h_version <= V3)
				branch (success);
		else
				store (success);

}/* z_restore */

void init_restore(void)
{
	zword success;
	
	if (!f_setup.restore_file)
		return;
	
	success = restore_quetzal (f_setup.restore_file, story_fp, blorb_ofs);
	if (!success)
		os_fatal("Error reading save file");
	
	fclose(f_setup.restore_file);
	
	store(success);
}

/*
 * mem_diff
 *
 * Set diff to a Quetzal-like difference between a and b,
 * copying a to b as we go.  It is assumed that diff points to a
 * buffer which is large enough to hold the diff.
 * mem_size is the number of bytes to compare.
 * Returns the number of bytes copied to diff.
 *
 */

static long mem_diff (zbyte *a, zbyte *b, zword mem_size, zbyte *diff)
{
		unsigned size = mem_size;
		zbyte *p = diff;
		unsigned j;
		zbyte c;

		for (;;) {
				for (j = 0; size > 0 && (c = *a++ ^ *b++) == 0; j++)
						size--;
				if (size == 0) break;
				size--;
				if (j > 0x8000) {
						*p++ = 0;
						*p++ = 0xff;
						*p++ = 0xff;
						j -= 0x8000;
				}
				if (j > 0) {
						*p++ = 0;
						j--;
						if (j <= 0x7f) {
								*p++ = j;
						} else {
								*p++ = (j & 0x7f) | 0x80;
								*p++ = (j & 0x7f80) >> 7;
						}
				}
				*p++ = c;
				*(b - 1) ^= c;
		}
		return p - diff;
}/* mem_diff */

/*
 * mem_undiff
 *
 * Applies a quetzal-like diff to dest
 *
 */

static void mem_undiff (zbyte *diff, long diff_length, zbyte *dest)
{
		zbyte c;

		while (diff_length) {
				c = *diff++;
				diff_length--;
				if (c == 0) {
						unsigned runlen;

						if (!diff_length)
								return;  /* Incomplete run */
						runlen = *diff++;
						diff_length--;
						if (runlen & 0x80) {
								if (!diff_length)
										return; /* Incomplete extended run */
								c = *diff++;
								diff_length--;
								runlen = (runlen & 0x7f) | (((unsigned) c) << 7);
						}

						dest += runlen + 1;
				} else {
						*dest++ ^= c;
				}
		}
}/* mem_undiff */

/*
 * restore_undo
 *
 * This function does the dirty work for z_restore_undo.
 *
 */

int restore_undo (void)
{

		if (f_setup.undo_slots == 0)		/* undo feature unavailable */

				return -1;

		if (curr_undo == NULL)				/* no saved game state */

				return 0;

		/* undo possible */

		memcpy (zmp, prev_zmp, h_dynamic_size);
		SET_PC (curr_undo->pc);
		sp = stack + STACK_SIZE - curr_undo->stack_size;
		fp = stack + curr_undo->frame_offset;
		frame_count = curr_undo->frame_count;
		mem_undiff ((zbyte *) (curr_undo + 1), curr_undo->diff_size, prev_zmp);
		memcpy (sp, (zbyte *)(curr_undo + 1) + curr_undo->diff_size,
						curr_undo->stack_size * sizeof (*sp));

		curr_undo = curr_undo->prev;

		restart_header ();

		return 2;

}/* restore_undo */

/*
 * z_restore_undo, restore a Z-machine state from memory.
 *
 *		no zargs used
 *
 */

void z_restore_undo (void)
{

		store ((zword) restore_undo ());

}/* z_restore_undo */

/*
 * z_save, save [a part of] the Z-machine state to disk.
 *
 *		zargs[0] = address of memory area to save (optional)
 *		zargs[1] = number of bytes to save
 *		zargs[2] = address of suggested file name
 *
 */

void z_save (void)
{
		FILE *gfp;

		zword success = 0;

		if (zargc != 0) {

				/* Open auxilary file */

				if ((gfp = frotzopenprompt (FILE_SAVE_AUX)) == NULL)
						goto finished;

				/* Write auxilary file */

				success = fwrite (zmp + zargs[0], zargs[1], 1, gfp);

				/* Close auxilary file */

				fclose (gfp);

		} else {

				long pc;
				zword addr;
				zword nsp, nfp;
				int skip;
				int i;

				/* Open game file */

				if ((gfp = frotzopenprompt (FILE_SAVE)) == NULL)
						goto finished;

				if (f_setup.save_quetzal) {
						success = save_quetzal (gfp, story_fp, blorb_ofs);
				} else {
						/* Write game file */

						fputc ((int) hi (h_release), gfp);
						fputc ((int) lo (h_release), gfp);
						fputc ((int) hi (h_checksum), gfp);
						fputc ((int) lo (h_checksum), gfp);

						GET_PC (pc)

								fputc ((int) (pc >> 16) & 0xff, gfp);
						fputc ((int) (pc >> 8) & 0xff, gfp);
						fputc ((int) (pc) & 0xff, gfp);

						nsp = (int) (sp - stack);
						nfp = (int) (fp - stack);

						fputc ((int) hi (nsp), gfp);
						fputc ((int) lo (nsp), gfp);
						fputc ((int) hi (nfp), gfp);
						fputc ((int) lo (nfp), gfp);

						for (i = nsp; i < STACK_SIZE; i++) {
								fputc ((int) hi (stack[i]), gfp);
								fputc ((int) lo (stack[i]), gfp);
						}

						fseek (story_fp, blorb_ofs, SEEK_SET);

						for (addr = 0, skip = 0; addr < h_dynamic_size; addr++)
								if (zmp[addr] != fgetc (story_fp) || skip == 255 || addr + 1 == h_dynamic_size) {
										fputc (skip, gfp);
										fputc (zmp[addr], gfp);
										skip = 0;
								} else skip++;
				}

				/* Close game file and check for errors */

				if (fclose (gfp) == EOF || ferror (story_fp)) {
						print_string ("Error writing save file\n");
						goto finished;
				}

				/* Success */

				success = 1;

		}

finished:

		if (h_version <= V3)
				branch (success);
		else
				store (success);

}/* z_save */

/*
 * save_undo
 *
 * This function does the dirty work for z_save_undo.
 *
 */

int save_undo (void)
{
		long diff_size;
		zword stack_size;
		undo_t *p;

		if (f_setup.undo_slots == 0)		/* undo feature unavailable */
				return -1;

		/* save undo possible */

		while (last_undo != curr_undo) {
				p = last_undo;
				last_undo = last_undo->prev;
				free (p);
				undo_count--;
		}
		if (last_undo)
				last_undo->next = NULL;
		else
				first_undo = NULL;

		if (undo_count == f_setup.undo_slots)
				free_undo (1);

		diff_size = mem_diff (zmp, prev_zmp, h_dynamic_size, undo_diff);
		stack_size = stack + STACK_SIZE - sp;
		do {
				p = malloc (sizeof (undo_t) + diff_size + stack_size * sizeof (*sp));
				if (p == NULL)
						free_undo (1);
		} while (!p && undo_count);
		if (p == NULL)
				return -1;
		GET_PC (p->pc)
				p->frame_count = frame_count;
		p->diff_size = diff_size;
		p->stack_size = stack_size;
		p->frame_offset = fp - stack;
		memcpy (p + 1, undo_diff, diff_size);
		memcpy ((zbyte *)(p + 1) + diff_size, sp, stack_size * sizeof (*sp));

		if (!first_undo) {
				p->prev = NULL;
				first_undo = p;
		} else {
				last_undo->next = p;
				p->prev = last_undo;
		}
		p->next = NULL;
		curr_undo = last_undo = p;
		undo_count++;
		return 1;

}/* save_undo */

/*
 * z_save_undo, save the current Z-machine state for a future undo.
 *
 *		no zargs used
 *
 */

void z_save_undo (void)
{

		store ((zword) save_undo ());

}/* z_save_undo */

/*
 * z_verify, check the story file integrity.
 *
 *		no zargs used
 *
 */

void z_verify (void)
{
		zword checksum = 0;
		long i;

		/* Sum all bytes in story file except header bytes */

		fseek (story_fp, blorb_ofs + 64, SEEK_SET);

		for (i = 64; i < story_size; i++)
				checksum += fgetc (story_fp);

		/* Branch if the checksums are equal */

		branch (checksum == h_checksum);

}/* z_verify */
