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WPCchecksumCorrection.cpp
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// based on java source by maddes
// checks and corrects, and optionally writes checksum corrected rom for WPC based machines
// arguments: wpc_cc.exe in.rom [out.rom]
#include <vector>
#define DEVELOPMENT_CHECKSUM 0x00FF
static unsigned short calcShortChecksum(const std::vector<unsigned char>& data)
{
unsigned short sum = 0;
for (size_t i = 0; i < data.size(); i++)
sum += data[i];
return sum;
}
static unsigned short getShort(const unsigned char* const ary, const unsigned int ofs)
{
return ((unsigned short)(ary[ofs]) << 8) | (unsigned short)(ary[ofs+1]);
}
static char* toHex(const unsigned char c)
{
if (c <= 0xF)
return "0";
else
return "";
}
static char* toHex(const unsigned short c)
{
if (c <= 0xF)
return "000";
else if (c <= 0xFF)
return "00";
else if (c <= 0xFFF)
return "0";
else
return "";
}
int main(int argc, char* argv[])
{
FILE* fp;
fopen_s(&fp, argv[1], "rb");
fseek(fp, 0u, SEEK_END);
const size_t size = ftell(fp);
fseek(fp, 0u, SEEK_SET);
std::vector<unsigned char> data;
data.resize(size);
fread(data.data(), 1u, size, fp);
fclose(fp);
// calculate checksum/correction offsets
const unsigned int ofsCO_high = size - 20;
const unsigned int ofsCO_low = ofsCO_high + 1;
const unsigned int ofsCS_high = ofsCO_low + 1;
const unsigned int ofsCS_low = ofsCS_high + 1;
// Validate checksum
printf("Read correction: %s%X%s%X\n", toHex(data[ofsCO_high]), data[ofsCO_high], toHex(data[ofsCO_low]), data[ofsCO_low]);
printf("Read checksum: %s%X%s%X is ", toHex(data[ofsCS_high]), data[ofsCS_high], toHex(data[ofsCS_low]), data[ofsCS_low]);
const unsigned short dataCSorg = getShort(data.data(), ofsCS_high);
const unsigned short dataCOorg = getShort(data.data(), ofsCO_high);
const unsigned short CalcCSorg = calcShortChecksum(data);
bool checksum_ok = true;
if (CalcCSorg != dataCSorg)
checksum_ok = false;
else if (data[ofsCO_low] != 0xFF - data[ofsCS_high])
checksum_ok = false;
else if (dataCOorg == DEVELOPMENT_CHECKSUM)
checksum_ok = false;
if (!checksum_ok)
{
printf("INVALID!!!\n\n");
printf("Calculated checksum: %s%X\n\n", toHex(CalcCSorg), CalcCSorg);
}
else
printf("OK!\n\n");
// start correcting
const unsigned char lowbyte = data[ofsCS_low];
printf("Re-calculating checksum for version low byte %s%X\n",toHex(lowbyte),lowbyte);
// Initialize ROM for checksum calculation
data[ofsCO_high] = 0x00;
data[ofsCO_low] = 0xFF;
data[ofsCS_high] = 0x00;
data[ofsCS_low] = 0xFF;
printf(" Initializing ROM...\n");
printf(" Correction slot: %s%X%s%X\n",toHex(data[ofsCO_high]),data[ofsCO_high],toHex(data[ofsCO_low]),data[ofsCO_low]);
printf(" Checksum slot: %s%X%s%X\n",toHex(data[ofsCS_high]),data[ofsCS_high],toHex(data[ofsCS_low]),data[ofsCS_low]);
// Get checksum for initialized ROM
const unsigned short calcCS = calcShortChecksum(data);
printf(" Calculated checksum: %s%X\n",toHex(calcCS),calcCS);
// Calculate 100% Williams style checksum and correction
printf(" Calculating Williams style checksum...\n");
// CO high byte (compensates CS low byte)
// CO high byte = 0xFF - CS low byte
data[ofsCO_high] = 0xFF - (calcCS & 0xFF);
printf(" Correction high byte: FF - %s%X = %s%X\n",toHex((unsigned char)(calcCS & 0xFF)),calcCS & 0xFF,toHex(data[ofsCO_high]),data[ofsCO_high]);
// CS low byte (can be set to anything as it was compensated to zero difference before)
data[ofsCS_low] = lowbyte;
// CS high byte
data[ofsCS_high] = (calcCS >> 8) & 0xFF;
// CO low byte (compensates CS high byte)
// CO low byte = 0xFF - CS high byte
data[ofsCO_low] = 0xFF - data[ofsCS_high];
printf(" Correction low byte: FF - %s%X = %s%X\n\n",toHex(data[ofsCS_high]),data[ofsCS_high],toHex(data[ofsCO_low]),data[ofsCO_low]);
printf("Final correction: %s%X%s%X\n",toHex(data[ofsCO_high]),data[ofsCO_high],toHex(data[ofsCO_low]),data[ofsCO_low]);
printf("Final checksum: %s%X%s%X is ",toHex(data[ofsCS_high]),data[ofsCS_high],toHex(data[ofsCS_low]),data[ofsCS_low]);
// Validate checksum
const unsigned short dataCS = getShort(data.data(), ofsCS_high);
const unsigned short dataCO = getShort(data.data(), ofsCO_high);
const unsigned short newCalcCS = calcShortChecksum(data);
checksum_ok = true;
if (newCalcCS != dataCS)
checksum_ok = false;
else if (data[ofsCO_low] != 0xFF - data[ofsCS_high])
checksum_ok = false;
else if (dataCO == DEVELOPMENT_CHECKSUM)
checksum_ok = false;
if (!checksum_ok)
{
printf("INVALID!!!\n\n");
printf("Calculated checksum: %s%X\n", toHex(newCalcCS),newCalcCS);
}
else
printf("OK!\n");
// optionally, write corrected file
if((argc >= 3) && (argv[2]))
{
fopen_s(&fp, argv[2], "wb");
fwrite(data.data(), 1u, size, fp);
fclose(fp);
}
}