scummvm/sword2/memory.cpp

/* Copyright (C) 1994-2004 Revolution Software Ltd
 *
 * 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 2
 * 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, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 *
 * $Header$
 */

// The new memory manager, now only used by the resource manager. Unlike the
// original, this one does not allocate a 12 MB memory pool at startup.
//
// There is one thing that prevents us from replacing the whole memory manager
// with the standard memory allocation functions: Broken Sword II absolutely,
// positively needs to be able to encode pointers as 32-bit integers. The
// original engine did this simply by casting between pointers and integers,
// but as far as I know that's not a very portable thing to do.
//
// For a while I was hopeing that the engine only needed pointers as function
// parameters, in which case I could have extended the stack to use a struct or
// a union instead, but no such luck. There is code in walker.cpp that
// obviously violates that assumption, and there are probably other, more
// well-hidden places, as well.
//
// This attacks the problem from the direction of another limitation in the
// original memory manager: it could only handle up to 999 blocks of memory.
// This memory manager has the same limitation, although it's probably way too
// large now, which means that a pointer can be encoded as 10 bits to store the
// block id, and another 22 bits to store an index into that block.

#include "common/stdafx.h"
#include "sword2/sword2.h"
#include "sword2/console.h"

namespace Sword2 {

#define MAX_BLOCKS 999

#define Debug_Printf _vm->_debugger->DebugPrintf

MemoryManager::MemoryManager(Sword2Engine *vm) : _vm(vm) {
	_memBlocks = (MemBlock *) malloc(MAX_BLOCKS * sizeof(MemBlock));
	_memBlockIndex = (MemBlock **) malloc(MAX_BLOCKS * sizeof(MemBlock *));
	_idStack = (int16 *) malloc(MAX_BLOCKS * sizeof(int16));

	_totAlloc = 0;
	_numBlocks = 0;

	for (int i = 0; i < MAX_BLOCKS; i++) {
		_idStack[i] = MAX_BLOCKS - i - 1;
		_memBlocks[i].ptr = NULL;
		_memBlockIndex[i] = NULL;
	}

	_idStackPtr = MAX_BLOCKS;
}

MemoryManager::~MemoryManager() {
	for (int i = 0; i < MAX_BLOCKS; i++)
		free(_memBlocks[i].ptr);
	free(_memBlocks);
	free(_memBlockIndex);
	free(_idStack);
}

int32 MemoryManager::encodePtr(byte *ptr) {
	int idx = findPointerInIndex(ptr);

	if (idx == -1)
		error("Encoding non-allocated pointer %p", ptr);

	int id = _memBlockIndex[idx]->id;

	return (id << 22) | (ptr - _memBlocks[id].ptr);
}

byte *MemoryManager::decodePtr(int32 n) {
	int16 id = (n >> 22) & 0x03ff;
	int32 offset = n & 0x003fffff;

	return _memBlocks[id].ptr + offset;
}

int16 MemoryManager::findExactPointerInIndex(byte *ptr) {
	int left = 0;
	int right = _numBlocks - 1;

	while (right >= left) {
		int n = (left + right) / 2;

		if (_memBlockIndex[n]->ptr == ptr)
			return n;

		if (_memBlockIndex[n]->ptr > ptr)
			right = n - 1;
		else
			left = n + 1;
	}

	return -1;
}

int16 MemoryManager::findPointerInIndex(byte *ptr) {
	int left = 0;
	int right = _numBlocks - 1;

	while (right >= left) {
		int n = (left + right) / 2;

		if (_memBlockIndex[n]->ptr <= ptr && _memBlockIndex[n]->ptr + _memBlockIndex[n]->size > ptr)
			return n;

		if (_memBlockIndex[n]->ptr > ptr)
			right = n - 1;
		else
			left = n + 1;
	}

	return -1;
}

int16 MemoryManager::findInsertionPointInIndex(byte *ptr) {
	if (_numBlocks == 0)
		return 0;

	int left = 0;
	int right = _numBlocks - 1;
	int n = 0;

	while (right >= left) {
		n = (left + right) / 2;

		if (_memBlockIndex[n]->ptr == ptr)
			return -1;

		if (_memBlockIndex[n]->ptr > ptr)
			right = n - 1;
		else
			left = n + 1;
	}

	if (_memBlockIndex[n]->ptr < ptr)
		n++;

	return n;
}

byte *MemoryManager::memAlloc(uint32 size, int16 uid) {
	byte *ptr = (byte *) malloc(size);

	assert(ptr);
	assert(_idStackPtr > 0);

	// Get the new block's id from the stack.
	int16 id = _idStack[--_idStackPtr];

	_memBlocks[id].id = id;
	_memBlocks[id].uid = uid;
	_memBlocks[id].ptr = ptr;
	_memBlocks[id].size = size;

	// The memory index provides a method for figuring out which memory
	// block an arbitrary pointer points to. A balanced tree might be more
	// efficient, but such beasts are tricky to implement.

	int16 idx = findInsertionPointInIndex(ptr);

	assert(idx != -1);

	for (int i = _numBlocks; i > idx; i--)
		_memBlockIndex[i] = _memBlockIndex[i - 1];

	_memBlockIndex[idx] = &_memBlocks[id];
	_numBlocks++;
	_totAlloc += size;

	return _memBlocks[id].ptr;
}

void MemoryManager::memFree(byte *ptr) {
	int16 idx = findExactPointerInIndex(ptr);

	if (idx == -1) {
		warning("Freeing non-allocated pointer %p", ptr);
		return;
	}

	// Put back the id on the stack
	_idStack[_idStackPtr++] = _memBlockIndex[idx]->id;

	free(_memBlockIndex[idx]->ptr);
	_memBlockIndex[idx]->ptr = NULL;

	_totAlloc -= _memBlockIndex[idx]->size;
	
	// Remove the pointer from the index
	_numBlocks--;

	for (int i = idx; i < _numBlocks; i++)
		_memBlockIndex[i] = _memBlockIndex[i + 1];
}

void MemoryManager::memDisplay() {
	for (int i = 0; i < _numBlocks; i++)
		Debug_Printf("%d: %ld bytes allocated by resource %d\n", i, _memBlocks[i].size, _memBlocks[i].uid);
}

void MemoryManager::memStatusStr(char *buf) {
	if (_totAlloc < 1024)
		sprintf(buf, "%u bytes in %d memory blocks", _totAlloc, _numBlocks);
	else if (_totAlloc < 1048576)
		sprintf(buf, "%uK in %d memory blocks", _totAlloc / 1024, _numBlocks);
	else
		sprintf(buf, "%.02fM in %d memory blocks", _totAlloc / 1048576., _numBlocks);
}

} // End of namespace Sword2