scummvm/engines/glk/glulx/serial.cpp

/* ScummVM - Graphic Adventure Engine
 *
 * ScummVM is the legal property of its developers, whose names
 * are too numerous to list here. Please refer to the COPYRIGHT
 * file distributed with this source distribution.
 *
 * This program 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 3 of the License, or
 * (at your option) any later version.
 *
 * This program 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, see <http://www.gnu.org/licenses/>.
 *
 */

#include "glk/glulx/glulx.h"

namespace Glk {
namespace Glulx {

#define IFFID(c1, c2, c3, c4) MKTAG(c1, c2, c3, c4)

bool Glulx::init_serial() {
	undo_chain_num = 0;
	undo_chain_size = max_undo_level;
	undo_chain = (unsigned char **)glulx_malloc(sizeof(unsigned char *) * undo_chain_size);
	if (!undo_chain)
		return false;

#ifdef SERIALIZE_CACHE_RAM
	{
		uint len = (endmem - ramstart);
		uint res;
		ramcache = (unsigned char *)glulx_malloc(sizeof(unsigned char *) * len);
		if (!ramcache)
			return false;

		_gameFile.seek(gamefile_start + ramstart);
		res = _gameFile.read(ramcache, len);
		if (res != len)
			return false;
	}
#endif /* SERIALIZE_CACHE_RAM */

	return true;
}

void Glulx::final_serial() {
	if (undo_chain) {
		int ix;
		for (ix = 0; ix < undo_chain_num; ix++) {
			glulx_free(undo_chain[ix]);
		}
		glulx_free(undo_chain);
	}
	undo_chain = nullptr;
	undo_chain_size = 0;
	undo_chain_num = 0;

#ifdef SERIALIZE_CACHE_RAM
	if (ramcache) {
		glulx_free(ramcache);
		ramcache = nullptr;
	}
#endif /* SERIALIZE_CACHE_RAM */
}

uint Glulx::perform_saveundo() {
	dest_t dest;
	uint res;
	uint memstart = 0, memlen = 0, heapstart = 0, heaplen = 0;
	uint stackstart = 0, stacklen = 0;

	/* The format for undo-saves is simpler than for saves on disk. We
	   just have a memory chunk, a heap chunk, and a stack chunk, in
	   that order. We skip the IFF chunk headers (although the size
	   fields are still there.) We also don't bother with IFF's 16-bit
	   alignment. */

	if (undo_chain_size == 0)
		return 1;

	dest._isMem = true;

	res = 0;
	if (res == 0) {
		res = write_long(&dest, 0); /* space for chunk length */
	}
	if (res == 0) {
		memstart = dest._pos;
		res = write_memstate(&dest);
		memlen = dest._pos - memstart;
	}
	if (res == 0) {
		res = write_long(&dest, 0); /* space for chunk length */
	}
	if (res == 0) {
		heapstart = dest._pos;
		res = write_heapstate(&dest, false);
		heaplen = dest._pos - heapstart;
	}
	if (res == 0) {
		res = write_long(&dest, 0); /* space for chunk length */
	}
	if (res == 0) {
		stackstart = dest._pos;
		res = write_stackstate(&dest, false);
		stacklen = dest._pos - stackstart;
	}

	if (res == 0) {
		/* Trim it down to the perfect size. */
		dest._ptr = (byte *)glulx_realloc(dest._ptr, dest._pos);
		if (!dest._ptr)
			res = 1;
	}
	if (res == 0) {
		res = reposition_write(&dest, memstart - 4);
	}
	if (res == 0) {
		res = write_long(&dest, memlen);
	}
	if (res == 0) {
		res = reposition_write(&dest, heapstart - 4);
	}
	if (res == 0) {
		res = write_long(&dest, heaplen);
	}
	if (res == 0) {
		res = reposition_write(&dest, stackstart - 4);
	}
	if (res == 0) {
		res = write_long(&dest, stacklen);
	}

	if (res == 0) {
		/* It worked. */
		if (undo_chain_num >= undo_chain_size) {
			glulx_free(undo_chain[undo_chain_num - 1]);
			undo_chain[undo_chain_num - 1] = nullptr;
		}
		if (undo_chain_size > 1)
			memmove(undo_chain + 1, undo_chain,
			        (undo_chain_size - 1) * sizeof(unsigned char *));
		undo_chain[0] = dest._ptr;
		if (undo_chain_num < undo_chain_size)
			undo_chain_num += 1;
		dest._ptr = nullptr;
	} else {
		/* It didn't work. */
		if (dest._ptr) {
			glulx_free(dest._ptr);
			dest._ptr = nullptr;
		}
	}

	return res;
}

uint Glulx::perform_restoreundo() {
	dest_t dest;
	uint res, val = 0;
	uint heapsumlen = 0;
	uint *heapsumarr = nullptr;

	/* If profiling is enabled and active then fail. */
#ifdef VM_PROFILING
	if (profile_profiling_active())
		return 1;
#endif /* VM_PROFILING */

	if (undo_chain_size == 0 || undo_chain_num == 0)
		return 1;

	dest._isMem = true;
	dest._ptr = undo_chain[0];

	res = 0;
	if (res == 0) {
		res = read_long(&dest, &val);
	}
	if (res == 0) {
		res = read_memstate(&dest, val);
	}
	if (res == 0) {
		res = read_long(&dest, &val);
	}
	if (res == 0) {
		res = read_heapstate(&dest, val, false, &heapsumlen, &heapsumarr);
	}
	if (res == 0) {
		res = read_long(&dest, &val);
	}
	if (res == 0) {
		res = read_stackstate(&dest, val, false);
	}
	/* ### really, many of the failure modes of those calls ought to
	   cause fatal errors. The stack or main memory may be damaged now. */

	if (res == 0) {
		if (heapsumarr)
			res = heap_apply_summary(heapsumlen, heapsumarr);
	}

	if (res == 0) {
		/* It worked. */
		if (undo_chain_size > 1)
			memmove(undo_chain, undo_chain + 1,
			        (undo_chain_size - 1) * sizeof(unsigned char *));
		undo_chain_num -= 1;
		glulx_free(dest._ptr);
		dest._ptr = nullptr;
	} else {
		/* It didn't work. */
		dest._ptr = nullptr;
	}

	return res;
}

Common::Error Glulx::readSaveData(Common::SeekableReadStream *rs) {
	Common::ErrorCode errCode = Common::kNoError;
	QuetzalReader r;
	if (r.open(rs))
		// Load in the savegame chunks
		errCode = loadGameChunks(r).getCode();

	return errCode;
}

Common::Error Glulx::writeGameData(Common::WriteStream *ws) {
	QuetzalWriter w;
	Common::ErrorCode errCode = saveGameChunks(w).getCode();

	if (errCode == Common::kNoError) {
		w.save(ws, _savegameDescription);
	}

	return errCode;
}

Common::Error Glulx::loadGameChunks(QuetzalReader &quetzal) {
	uint res = 0;
	uint heapsumlen = 0;
	uint *heapsumarr = nullptr;

	for (QuetzalReader::Iterator it = quetzal.begin();
			it != quetzal.end() && !res; ++it) {
		Common::SeekableReadStream *rs = it.getStream();
		dest_t dest;
		dest._src = rs;

		switch ((*it)._id) {
		case ID_IFhd:
			for (int ix = 0; ix < 128 && !res; ix++) {
				byte v = rs->readByte();
				if (Mem1(ix) != v)
					// ### non-matching header
					res = 1;
			}
			break;

		case ID_CMem:
			res = read_memstate(&dest, rs->size());
			break;

		case MKTAG('M', 'A', 'l', 'l'):
			res = read_heapstate(&dest, rs->size(), true, &heapsumlen, &heapsumarr);
			break;

		case ID_Stks:
			res = read_stackstate(&dest, rs->size(), true);
			break;

		default:
			break;
		}

		delete rs;
	}

	if (!res) {
		if (heapsumarr) {
			/* The summary might have come from any interpreter, so it could
			   be out of order. We'll sort it. */
			glulx_sort(heapsumarr + 2, (heapsumlen - 2) / 2, 2 * sizeof(uint), &sort_heap_summary);
			res = heap_apply_summary(heapsumlen, heapsumarr);
		}
	}

	return res ? Common::kReadingFailed : Common::kNoError;
}

Common::Error Glulx::saveGameChunks(QuetzalWriter &quetzal) {
	uint res = 0;

	// IFHd
	if (!res) {
		Common::WriteStream &ws = quetzal.add(ID_IFhd);
		for (int ix = 0; res == 0 && ix < 128; ix++)
			ws.writeByte(Mem1(ix));
	}

	// CMem
	if (!res) {
		Common::WriteStream &ws = quetzal.add(ID_CMem);
		dest_t dest;
		dest._dest = &ws;
		res = write_memstate(&dest);
	}

	// MAll
	if (!res) {
		Common::WriteStream &ws = quetzal.add(MKTAG('M', 'A', 'l', 'l'));
		dest_t dest;
		dest._dest = &ws;
		res = write_heapstate(&dest, true);
	}

	// Stks
	if (!res) {
		Common::WriteStream &ws = quetzal.add(ID_Stks);
		dest_t dest;
		dest._dest = &ws;
		res = write_stackstate(&dest, true);
	}

	// All done
	return res ? Common::kUnknownError : Common::kNoError;
}

int Glulx::reposition_write(dest_t *dest, uint pos) {
	if (dest->_isMem) {
		dest->_pos = pos;
	} else {
		error("Seeking a WriteStream isn't allowed");
	}

	return 0;
}

int Glulx::write_buffer(dest_t *dest, const byte *ptr, uint len) {
	if (dest->_isMem) {
		if (dest->_pos + len > dest->_size) {
			dest->_size = dest->_pos + len + 1024;
			if (!dest->_ptr) {
				dest->_ptr = (byte *)glulx_malloc(dest->_size);
			} else {
				dest->_ptr = (byte *)glulx_realloc(dest->_ptr, dest->_size);
			}
			if (!dest->_ptr)
				return 1;
		}
		memcpy(dest->_ptr + dest->_pos, ptr, len);
	} else {
		dest->_dest->write(ptr, len);
	}

	dest->_pos += len;

	return 0;
}

int Glulx::read_buffer(dest_t *dest, byte *ptr, uint len) {
	uint newlen;

	if (dest->_isMem) {
		memcpy(ptr, dest->_ptr + dest->_pos, len);
	} else {
		newlen = dest->_src->read(ptr, len);
		if (newlen != len)
			return 1;
	}

	dest->_pos += len;

	return 0;
}

int Glulx::write_long(dest_t *dest, uint val) {
	unsigned char buf[4];
	Write4(buf, val);
	return write_buffer(dest, buf, 4);
}

int Glulx::write_short(dest_t *dest, uint16 val) {
	unsigned char buf[2];
	Write2(buf, val);
	return write_buffer(dest, buf, 2);
}

int Glulx::write_byte(dest_t *dest, byte val) {
	return write_buffer(dest, &val, 1);
}

int Glulx::read_long(dest_t *dest, uint *val) {
	unsigned char buf[4];
	int res = read_buffer(dest, buf, 4);
	if (res)
		return res;
	*val = Read4(buf);
	return 0;
}

int Glulx::read_short(dest_t *dest, uint16 *val) {
	unsigned char buf[2];
	int res = read_buffer(dest, buf, 2);
	if (res)
		return res;
	*val = Read2(buf);
	return 0;
}

int Glulx::read_byte(dest_t *dest, byte *val) {
	return read_buffer(dest, val, 1);
}

uint Glulx::write_memstate(dest_t *dest) {
	uint res, pos;
	int val;
	int runlen;
	unsigned char ch;
#ifdef SERIALIZE_CACHE_RAM
	uint cachepos;
#endif /* SERIALIZE_CACHE_RAM */

	res = write_long(dest, endmem);
	if (res)
		return res;

	runlen = 0;

#ifdef SERIALIZE_CACHE_RAM
	cachepos = 0;
#else /* SERIALIZE_CACHE_RAM */
	_gameFile.seek(gamefile_start + ramstart);
#endif /* SERIALIZE_CACHE_RAM */

	for (pos = ramstart; pos < endmem; pos++) {
		ch = Mem1(pos);
		if (pos < endgamefile) {
#ifdef SERIALIZE_CACHE_RAM
			val = ramcache[cachepos];
			cachepos++;
#else /* SERIALIZE_CACHE_RAM */
			val = glk_get_char_stream(gamefile);
			if (val == -1) {
				fatal_error("The game file ended unexpectedly while saving.");
			}
#endif /* SERIALIZE_CACHE_RAM */
			ch ^= (unsigned char)val;
		}
		if (ch == 0) {
			runlen++;
		} else {
			/* Write any run we've got. */
			while (runlen) {
				if (runlen >= 0x100)
					val = 0x100;
				else
					val = runlen;
				res = write_byte(dest, 0);
				if (res)
					return res;
				res = write_byte(dest, (val - 1));
				if (res)
					return res;
				runlen -= val;
			}
			/* Write the byte we got. */
			res = write_byte(dest, ch);
			if (res)
				return res;
		}
	}
	/* It's possible we've got a run left over, but we don't write it. */

	return 0;
}

uint Glulx::read_memstate(dest_t *dest, uint chunklen) {
	uint chunkend = dest->_pos + chunklen;
	uint newlen;
	uint res, pos;
	int val;
	int runlen;
	unsigned char ch, ch2;
#ifdef SERIALIZE_CACHE_RAM
	uint cachepos;
#endif /* SERIALIZE_CACHE_RAM */

	heap_clear();

	res = read_long(dest, &newlen);
	if (res)
		return res;

	res = change_memsize(newlen, false);
	if (res)
		return res;

	runlen = 0;

#ifdef SERIALIZE_CACHE_RAM
	cachepos = 0;
#else /* SERIALIZE_CACHE_RAM */
	_gameFile.seek(gamefile_start + ramstart);
#endif /* SERIALIZE_CACHE_RAM */

	for (pos = ramstart; pos < endmem; pos++) {
		if (pos < endgamefile) {
#ifdef SERIALIZE_CACHE_RAM
			val = ramcache[cachepos];
			cachepos++;
#else /* SERIALIZE_CACHE_RAM */
			if (_gameFile.pos() >= _gameFile.size()) {
				fatal_error("The game file ended unexpectedly while restoring.");
				val = _gameFile.readByte();
			}
#endif /* SERIALIZE_CACHE_RAM */
			ch = (unsigned char)val;
		} else {
			ch = 0;
		}

		if (dest->_pos >= chunkend) {
			/* we're into the final, unstored run. */
		} else if (runlen) {
			runlen--;
		} else {
			res = read_byte(dest, &ch2);
			if (res)
				return res;
			if (ch2 == 0) {
				res = read_byte(dest, &ch2);
				if (res)
					return res;
				runlen = (uint)ch2;
			} else {
				ch ^= ch2;
			}
		}

		if (pos >= protectstart && pos < protectend)
			continue;

		MemW1(pos, ch);
	}

	return 0;
}

uint Glulx::write_heapstate(dest_t *dest, int portable) {
	uint res;
	uint sumlen;
	uint *sumarray;

	res = heap_get_summary(&sumlen, &sumarray);
	if (res)
		return res;

	if (!sumarray)
		return 0; /* no heap */

	res = write_heapstate_sub(sumlen, sumarray, dest, portable);

	glulx_free(sumarray);
	return res;
}

uint Glulx::write_heapstate_sub(uint sumlen, uint *sumarray, dest_t *dest, int portable)  {
	uint res, lx;

	/* If we're storing for the purpose of undo, we don't need to do any
	   byte-swapping, because the result will only be used by this session. */
	if (!portable) {
		res = write_buffer(dest, (const byte *)sumarray, sumlen * sizeof(uint));
		if (res)
			return res;
		return 0;
	}

	for (lx = 0; lx < sumlen; lx++) {
		res = write_long(dest, sumarray[lx]);
		if (res)
			return res;
	}

	return 0;
}

int Glulx::sort_heap_summary(const void *p1, const void *p2) {
	uint v1 = *(const uint *)p1;
	uint v2 = *(const uint *)p2;

	if (v1 < v2)
		return -1;
	if (v1 > v2)
		return 1;
	return 0;
}

uint Glulx::read_heapstate(dest_t *dest, uint chunklen, int portable, uint *sumlen, uint **summary) {
	uint res, count, lx;
	uint *arr;

	*sumlen = 0;
	*summary = nullptr;

	if (chunklen == 0)
		return 0; /* no heap */

	if (!portable) {
		count = chunklen / sizeof(uint);

		arr = (uint *)glulx_malloc(chunklen);
		if (!arr)
			return 1;

		res = read_buffer(dest, (byte *)arr, chunklen);
		if (res)
			return res;

		*sumlen = count;
		*summary = arr;

		return 0;
	}

	count = chunklen / 4;

	arr = (uint *)glulx_malloc(count * sizeof(uint));
	if (!arr)
		return 1;

	for (lx = 0; lx < count; lx++) {
		res = read_long(dest, arr + lx);
		if (res)
			return res;
	}

	*sumlen = count;
	*summary = arr;

	return 0;
}

uint Glulx::write_stackstate(dest_t *dest, int portable) {
	uint res;
	uint lx;
	uint lastframe;

	/* If we're storing for the purpose of undo, we don't need to do any
	   byte-swapping, because the result will only be used by this session. */
	if (!portable) {
		res = write_buffer(dest, stack, stackptr);
		if (res)
			return res;
		return 0;
	}

	/* Write a portable stack image. To do this, we have to write stack
	   frames in order, bottom to top. Remember that the last word of
	   every stack frame is a pointer to the beginning of that stack frame.
	   (This includes the last frame, because the save opcode pushes on
	   a call stub before it calls perform_save().) */

	lastframe = (uint)(-1);
	while (1) {
		uint frameend, frm, frm2, frm3;
		unsigned char loctype, loccount;
		uint numlocals, frlen, locpos;

		/* Find the next stack frame (after the one in lastframe). Sadly,
		   this requires searching the stack from the top down. We have to
		   do this for *every* frame, which takes N^2 time overall. But
		   save routines usually aren't nested very deep.
		   If it becomes a practical problem, we can build a stack-frame
		   array, which requires dynamic allocation. */
		for (frm = stackptr, frameend = stackptr;
		        frm != 0 && (frm2 = Stk4(frm - 4)) != lastframe;
		        frameend = frm, frm = frm2) { };

		/* Write out the frame. */
		frm2 = frm;

		frlen = Stk4(frm2);
		frm2 += 4;
		res = write_long(dest, frlen);
		if (res)
			return res;
		locpos = Stk4(frm2);
		frm2 += 4;
		res = write_long(dest, locpos);
		if (res)
			return res;

		frm3 = frm2;

		numlocals = 0;
		while (1) {
			loctype = Stk1(frm2);
			frm2 += 1;
			loccount = Stk1(frm2);
			frm2 += 1;

			res = write_byte(dest, loctype);
			if (res)
				return res;
			res = write_byte(dest, loccount);
			if (res)
				return res;

			if (loctype == 0 && loccount == 0)
				break;

			numlocals++;
		}

		if ((numlocals & 1) == 0) {
			res = write_byte(dest, 0);
			if (res)
				return res;
			res = write_byte(dest, 0);
			if (res)
				return res;
			frm2 += 2;
		}

		if (frm2 != frm + locpos)
			fatal_error("Inconsistent stack frame during save.");

		/* Write out the locals. */
		for (lx = 0; lx < numlocals; lx++) {
			loctype = Stk1(frm3);
			frm3 += 1;
			loccount = Stk1(frm3);
			frm3 += 1;

			if (loctype == 0 && loccount == 0)
				break;

			/* Put in up to 0, 1, or 3 bytes of padding, depending on loctype. */
			while (frm2 & (loctype - 1)) {
				res = write_byte(dest, 0);
				if (res)
					return res;
				frm2 += 1;
			}

			/* Put in this set of locals. */
			switch (loctype) {

			case 1:
				do {
					res = write_byte(dest, Stk1(frm2));
					if (res)
						return res;
					frm2 += 1;
					loccount--;
				} while (loccount);
				break;

			case 2:
				do {
					res = write_short(dest, Stk2(frm2));
					if (res)
						return res;
					frm2 += 2;
					loccount--;
				} while (loccount);
				break;

			case 4:
				do {
					res = write_long(dest, Stk4(frm2));
					if (res)
						return res;
					frm2 += 4;
					loccount--;
				} while (loccount);
				break;

			}
		}

		if (frm2 != frm + frlen)
			fatal_error("Inconsistent stack frame during save.");

		while (frm2 < frameend) {
			res = write_long(dest, Stk4(frm2));
			if (res)
				return res;
			frm2 += 4;
		}

		/* Go on to the next frame. */
		if (frameend == stackptr)
			break; /* All done. */
		lastframe = frm;
	}

	return 0;
}

uint Glulx::read_stackstate(dest_t *dest, uint chunklen, int portable) {
	uint res;
	uint frameend, frm, frm2, frm3, locpos, frlen, numlocals;

	if (chunklen > stacksize)
		return 1;

	stackptr = chunklen;
	frameptr = 0;
	valstackbase = 0;
	localsbase = 0;

	if (!portable) {
		res = read_buffer(dest, stack, stackptr);
		if (res)
			return res;
		return 0;
	}

	/* This isn't going to be pleasant; we're going to read the data in
	   as a block, and then convert it in-place. */
	res = read_buffer(dest, stack, stackptr);
	if (res)
		return res;

	frameend = stackptr;
	while (frameend != 0) {
		/* Read the beginning-of-frame pointer. Remember, right now, the
		   whole frame is stored big-endian. So we have to read with the
		   Read*() macros, and then write with the StkW*() macros. */
		frm = Read4(stack + (frameend - 4));

		frm2 = frm;

		frlen = Read4(stack + frm2);
		StkW4(frm2, frlen);
		frm2 += 4;
		locpos = Read4(stack + frm2);
		StkW4(frm2, locpos);
		frm2 += 4;

		/* The locals-format list is in bytes, so we don't have to convert it. */
		frm3 = frm2;
		frm2 = frm + locpos;

		numlocals = 0;

		while (1) {
			unsigned char loctype, loccount;
			loctype = Read1(stack + frm3);
			frm3 += 1;
			loccount = Read1(stack + frm3);
			frm3 += 1;

			if (loctype == 0 && loccount == 0)
				break;

			/* Skip up to 0, 1, or 3 bytes of padding, depending on loctype. */
			while (frm2 & (loctype - 1)) {
				StkW1(frm2, 0);
				frm2++;
			}

			/* Convert this set of locals. */
			switch (loctype) {

			case 1:
				do {
					/* Don't need to convert bytes. */
					frm2 += 1;
					loccount--;
				} while (loccount);
				break;

			case 2:
				do {
					uint16 loc = Read2(stack + frm2);
					StkW2(frm2, loc);
					frm2 += 2;
					loccount--;
				} while (loccount);
				break;

			case 4:
				do {
					uint loc = Read4(stack + frm2);
					StkW4(frm2, loc);
					frm2 += 4;
					loccount--;
				} while (loccount);
				break;

			}

			numlocals++;
		}

		if ((numlocals & 1) == 0) {
			StkW1(frm3, 0);
			frm3++;
			StkW1(frm3, 0);
			frm3++;
		}

		if (frm3 != frm + locpos) {
			return 1;
		}

		while (frm2 & 3) {
			StkW1(frm2, 0);
			frm2++;
		}

		if (frm2 != frm + frlen) {
			return 1;
		}

		/* Now, the values pushed on the stack after the call frame itself.
		   This includes the stub. */
		while (frm2 < frameend) {
			uint loc = Read4(stack + frm2);
			StkW4(frm2, loc);
			frm2 += 4;
		}

		frameend = frm;
	}

	return 0;
}

uint Glulx::perform_verify() {
	uint len, chksum = 0, newlen;
	unsigned char buf[4];
	uint val, newsum, ix;

	len = gamefile_len;

	if (len < 256 || (len & 0xFF) != 0)
		return 1;

	_gameFile.seek(gamefile_start);
	newsum = 0;

	/* Read the header */
	for (ix = 0; ix < 9; ix++) {
		newlen = _gameFile.read(buf, 4);
		if (newlen != 4)
			return 1;
		val = Read4(buf);
		if (ix == 3) {
			if (len != val)
				return 1;
		}
		if (ix == 8)
			chksum = val;
		else
			newsum += val;
	}

	/* Read everything else */
	for (; ix < len / 4; ix++) {
		newlen = _gameFile.read(buf, 4);
		if (newlen != 4)
			return 1;
		val = Read4(buf);
		newsum += val;
	}

	if (newsum != chksum)
		return 1;

	return 0;
}

} // End of namespace Glulx
} // End of namespace Glk