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Christopher Kobayashi 2020-04-21 15:32:19 +09:00
parent 1d9a98569f
commit 0fe280bc5a
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Makefile Normal file
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CFLAGS= -O2 -Wall -Werror
all: dc42cksm
install: all
install -m755 dc42cksm /usr/local/bin/
clean:
rm -f dc42cksm *.o

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dc42cksm.c Normal file
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/* dc42cksm
A command-line program to view the checksums in a Macintosh Disk Copy 4.2
disk image file, and optionally to update the checksums if they’re not
correct.
Originally written by Steve Chamberlin <steve@bigmessowires.com>
64-bit-cleaned and lightly converted from C++ to C by Christopher RYU
*/
#include <stdio.h>
#include <stdlib.h>
#include <malloc.h>
#include <sys/types.h>
u_int8_t Read8(FILE* file)
{
u_int8_t b;
fread(&b, 1, 1, file);
return b;
}
u_int16_t ReadBigEndian16(FILE* file)
{
u_int8_t b[2];
fread(&b, 1, 2, file);
return (((u_int16_t)b[0]) << 8) | b[1];
}
u_int32_t ReadBigEndian32(FILE* file)
{
u_int8_t b[4];
fread(&b, 1, 4, file);
return (((u_int32_t)b[0]) << 24) | (((u_int32_t)b[1]) << 16) | (((u_int32_t)b[2]) << 8) | b[3];
}
void SetBigEndian32(u_int8_t* pDest, u_int32_t value)
{
pDest[0] = (value >> 24) & 0xFF;
pDest[1] = (value >> 16) & 0xFF;
pDest[2] = (value >> 8) & 0xFF;
pDest[3] = value & 0xFF;
}
int main(int argc, char* argv[])
{
/* parse the command line */
if (argc != 2)
{
printf("Disk Copy 4.2 checksum tool:\nVerifies and optionally updates checksums for DC42 disk image files.\n\n");
printf("Usage: %s filename\n", argv[0]);
return -1;
}
char *sourceFilename = argv[1];
printf("Verifying Disk Copy 4.2 disk image checksums for %s\n", sourceFilename);
FILE *pFile = fopen(sourceFilename, "rb");
if (!pFile)
{
printf("Could not open source file %s\n", sourceFilename);
return -1;
}
/* check the DC42 signature bytes */
fseek(pFile, 0x52, SEEK_SET);
u_int16_t magic0 = Read8(pFile);
u_int16_t magic1 = Read8(pFile);
if (magic0 != 1 || magic1 != 0)
{
printf("This doesn't look like a valid DC42 disk image file. Aborting.\n");
fclose(pFile);
return 0;
}
/* return to start */
fseek(pFile, 0, SEEK_SET);
/* disk image name */
u_int8_t nameLen = Read8(pFile);
unsigned char name[64];
fread(name, 1, 63, pFile);
if (nameLen < 64)
name[nameLen] = 0;
else
name[63] = 0;
printf(" stored image name: %s\n", name);
/* size of data and tag regions */
u_int32_t dataSize = ReadBigEndian32(pFile);
printf(" data size: %08X\n", dataSize);
u_int32_t tagSize = ReadBigEndian32(pFile);
printf(" tag size: %08X\n", tagSize);
/* stored checksums */
u_int32_t storedDataChecksum = ReadBigEndian32(pFile);
u_int32_t storedTagChecksum = ReadBigEndian32(pFile);
/* disk encoding */
u_int8_t encoding = Read8(pFile);
switch (encoding)
{
case 0:
printf(" encoding: 00, GCR single-sided double density 400K\n");
break;
case 1:
printf(" encoding: 01, GCR double-sided double density 800K\n");
break;
case 2:
printf(" encoding: 02, MFM double-sided double density 720K\n");
break;
case 3:
printf(" encoding: 03, MFM double-sided high density 1440K\n");
break;
default:
printf(" encoding: %02X, unknown\n", encoding);
break;
}
/* disk format */
u_int8_t format = Read8(pFile);
switch (format)
{
case 0x02:
printf(" format: 02, Macintosh/Lisa 400K\n");
break;
case 0x22:
printf(" format: 22, Macintosh 800K\n");
break;
case 0x24:
printf(" format: 24, ProDOS 800K\n");
break;
default:
printf(" format: %02X, unknown\n", format);
break;
}
/* ignore the magic number */
ReadBigEndian16(pFile);
/* compute the data checksum */
u_int32_t dataChecksum = 0;
for (u_int32_t i=0; i<dataSize; i+=2)
{
dataChecksum += ReadBigEndian16(pFile);
dataChecksum = (dataChecksum >> 1) | ((dataChecksum & 1) << 31);
}
/* compute the tag checksum */
u_int32_t tagChecksum = 0;
if (tagSize > 12)
{
/* skip the first 12 tag bytes */
for (int i=0; i<12; i++)
{
Read8(pFile);
}
for (u_int32_t i=12; i<tagSize; i+=2)
{
tagChecksum += ReadBigEndian16(pFile);
tagChecksum = (tagChecksum >> 1) | ((tagChecksum & 1) << 31);
}
}
/* show the results */
printf(" stored data checksum: %08X\n", storedDataChecksum);
printf("computed data checksum: %08X\n", dataChecksum);
printf(" stored tag checksum: %08X\n", storedTagChecksum);
printf(" computed tag checksum: %08X\n", tagChecksum);
if (storedDataChecksum == dataChecksum && storedTagChecksum == tagChecksum)
{
printf("\nVerification succeeded, no errors.\n");
}
else
{
printf("\nThe stored checksums do not match the computed checksums.\n");
printf("\nUpdate the stored checksums? (Y/N) ");
u_int8_t a = getchar();
if (a == 'y' || a =='Y')
{
/* read the whole file into memory */
u_int32_t bufSize = 0x54 + dataSize + tagSize;
u_int8_t* pBuffer = (u_int8_t*)malloc(bufSize);
if (pBuffer == 0)
{
printf("error: couldn't allocate %u bytes\n", bufSize);
return -1;
}
fseek(pFile, 0, SEEK_SET);
fread(pBuffer, bufSize, 1, pFile);
fclose(pFile);
/* modify the checksums */
SetBigEndian32(&pBuffer[0x48], dataChecksum);
SetBigEndian32(&pBuffer[0x4C], tagChecksum);
/* write the modified file */
FILE *pFile = fopen(sourceFilename, "wb");
if (!pFile)
{
printf("error: could not re-open file for writing\n");
return -1;
}
fwrite(pBuffer, bufSize, 1, pFile);
printf("%s was modified, checksums updated.\n", sourceFilename);
}
else
{
printf("%s was not modified.\n", sourceFilename);
}
}
fclose(pFile);
return 0;
}