RetroArch/bps.c
2011-12-25 01:38:59 +01:00

175 lines
5.1 KiB
C

/* SSNES - A Super Nintendo Entertainment System (SNES) Emulator frontend for libsnes.
* Copyright (C) 2010-2011 - Hans-Kristian Arntzen
*
* Some code herein may be based on code found in BSNES.
*
* SSNES 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 Found-
* ation, either version 3 of the License, or (at your option) any later version.
*
* SSNES 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 SSNES.
* If not, see <http://www.gnu.org/licenses/>.
*/
#include "bps.h"
#include "movie.h"
#include <stdint.h>
#include "boolean.h"
#include "msvc/msvc_compat.h"
enum bps_mode
{
SOURCE_READ = 0,
TARGET_READ,
SOURCE_COPY,
TARGET_COPY
};
struct bps_data
{
const uint8_t *modify_data, *source_data;
uint8_t *target_data;
size_t modify_length, source_length, target_length;
size_t modify_offset, source_offset, target_offset;
uint32_t modify_checksum, source_checksum, target_checksum;
size_t source_relative_offset, target_relative_offset, output_offset;
};
static uint8_t bps_read(struct bps_data *bps)
{
uint8_t data = bps->modify_data[bps->modify_offset++];
bps->modify_checksum = crc32_adjust(bps->modify_checksum, data);
return data;
}
static uint64_t bps_decode(struct bps_data *bps)
{
uint64_t data = 0, shift = 1;
for (;;)
{
uint8_t x = bps_read(bps);
data += (x & 0x7f) * shift;
if (x & 0x80)
break;
shift <<= 7;
data += shift;
}
return data;
}
static void bps_write(struct bps_data *bps, uint8_t data)
{
bps->target_data[bps->output_offset++] = data;
bps->target_checksum = crc32_adjust(bps->target_checksum, data);
}
bps_error_t bps_apply_patch(
const uint8_t *modify_data, size_t modify_length,
const uint8_t *source_data, size_t source_length,
uint8_t *target_data, size_t *target_length)
{
if (modify_length < 19)
return BPS_PATCH_TOO_SMALL;
struct bps_data bps = {0};
bps.modify_data = modify_data;
bps.modify_length = modify_length;
bps.target_data = target_data;
bps.target_length = *target_length;
bps.source_data = source_data;
bps.source_length = source_length;
bps.modify_checksum = ~0;
bps.target_checksum = ~0;
if ((bps_read(&bps) != 'B') || (bps_read(&bps) != 'P') || (bps_read(&bps) != 'S') || (bps_read(&bps) != '1'))
return BPS_PATCH_INVALID_HEADER;
size_t modify_source_size = bps_decode(&bps);
size_t modify_target_size = bps_decode(&bps);
size_t modify_markup_size = bps_decode(&bps);
for (size_t i = 0; i < modify_markup_size; i++)
bps_read(&bps);
if (modify_source_size > bps.source_length)
return BPS_SOURCE_TOO_SMALL;
if (modify_target_size > bps.target_length)
return BPS_TARGET_TOO_SMALL;
while (bps.modify_offset < bps.modify_length - 12)
{
size_t length = bps_decode(&bps);
unsigned mode = length & 3;
length = (length >> 2) + 1;
switch (mode)
{
case SOURCE_READ:
while (length--)
bps_write(&bps, bps.source_data[bps.output_offset]);
break;
case TARGET_READ:
while (length--)
bps_write(&bps, bps_read(&bps));
break;
case SOURCE_COPY:
case TARGET_COPY:
{
int offset = bps_decode(&bps);
bool negative = offset & 1;
offset >>= 1;
if (negative)
offset = -offset;
if (mode == SOURCE_COPY)
{
bps.source_offset += offset;
while (length--)
bps_write(&bps, bps.source_data[bps.source_offset++]);
}
else
{
bps.target_offset += offset;
while (length--)
bps_write(&bps, bps.target_data[bps.target_offset++]);
break;
}
break;
}
}
}
uint32_t modify_source_checksum = 0, modify_target_checksum = 0, modify_modify_checksum = 0;
for (unsigned i = 0; i < 32; i += 8)
modify_source_checksum |= bps_read(&bps) << i;
for (unsigned i = 0; i < 32; i += 8)
modify_target_checksum |= bps_read(&bps) << i;
uint32_t checksum = ~bps.modify_checksum;
for (unsigned i = 0; i < 32; i += 8)
modify_modify_checksum |= bps_read(&bps) << i;
bps.source_checksum = crc32_calculate(bps.source_data, bps.source_length);
bps.target_checksum = ~bps.target_checksum;
if (bps.source_checksum != modify_source_checksum)
return BPS_SOURCE_CHECKSUM_INVALID;
if (bps.target_checksum != modify_target_checksum)
return BPS_TARGET_CHECKSUM_INVALID;
if (checksum != modify_modify_checksum)
return BPS_PATCH_CHECKSUM_INVALID;
*target_length = modify_target_size;
return BPS_SUCCESS;
}