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Implement checksum validation method.

master
Ben Kurtovic 9 år sedan
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incheckning
ced62acfbb
2 ändrade filer med 44 tillägg och 8 borttagningar
  1. +42
    -8
      src/rom.c
  2. +2
    -0
      src/rom.h

+ 42
- 8
src/rom.c Visa fil

@@ -3,7 +3,6 @@

#include <ctype.h>
#include <errno.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
@@ -17,7 +16,7 @@
#define MAGIC_LEN 8
#define HEADER_SIZE 16

static size_t header_locations[NUM_LOCATIONS] = {0x7FF0, 0x1FF0, 0x3FF0};
static size_t header_locations[NUM_LOCATIONS] = {0x7FF0, 0x3FF0, 0x1FF0};
static const char header_magic[MAGIC_LEN + 1] = "TMR SEGA";

/*
@@ -57,23 +56,54 @@ static void print_header(const uint8_t *header)
#endif

/*
Return a string indicating the ROM's size, according to its header.
Determine whether the checksum indicated in the ROM file is valid.
*/
static bool validate_checksum(const uint8_t *data, uint16_t checksum, uint8_t size)
{
size_t low_region, high_region;
switch (size) {
case 0xA: low_region = 0x1FEF; high_region = 0; break;
case 0xB: low_region = 0x3FEF; high_region = 0; break;
case 0xC: low_region = 0x7FEF; high_region = 0; break;
case 0xD: low_region = 0xBFEF; high_region = 0; break;
case 0xE: low_region = 0x7FEF; high_region = 0x0FFFF; break;
case 0xF: low_region = 0x7FEF; high_region = 0x1FFFF; break;
case 0x0: low_region = 0x7FEF; high_region = 0x3FFFF; break;
case 0x1: low_region = 0x7FEF; high_region = 0x7FFFF; break;
case 0x2: low_region = 0x7FEF; high_region = 0xFFFFF; break;
default: return false;
}

uint16_t sum = 0;
for (size_t index = 0; index <= low_region; index++)
sum += data[index];
if (high_region) {
for (size_t index = 0x08000; index <= high_region; index++)
sum += data[index];
}
return sum == checksum;
}

#ifdef DEBUG_MODE
/*
DEBUG FUNCTION: Return the ROM's size as a string, according to its header.
*/
static const char* parse_reported_size(uint8_t value)
{
switch (value) {
case 0x0: return "256 KB";
case 0x1: return "512 KB";
case 0x2: return "1 MB";
case 0xA: return "8 KB";
case 0xB: return "16 KB";
case 0xC: return "32 KB";
case 0xD: return "48 KB";
case 0xE: return "64 KB";
case 0xF: return "128 KB";
case 0x0: return "256 KB";
case 0x1: return "512 KB";
case 0x2: return "1 MB";
default: return "Unknown";
}
}
#endif

/*
Parse a ROM image's header, and return whether or not it is valid.
@@ -106,7 +136,9 @@ static bool parse_header(ROM *rom, const uint8_t *header)
print_header(header);
#endif

uint8_t size = header[0xF] & 0xF;
rom->checksum = header[0xA] + (header[0xB] << 8);
rom->valid_checksum = validate_checksum(rom->data, rom->checksum, size);
rom->product_code = bcd_decode(header[0xC]) +
(bcd_decode(header[0xD]) * 100) + ((header[0xE] >> 4) * 10000);
rom->version = header[0xE] & 0x0F;
@@ -114,11 +146,12 @@ static bool parse_header(ROM *rom, const uint8_t *header)
const char* region = rom_region(rom);

DEBUG("- header info:")
DEBUG(" - checksum: 0x%04X", rom->checksum)
DEBUG(" - checksum: 0x%04X (%s)", rom->checksum,
rom->valid_checksum ? "valid" : "invalid")
DEBUG(" - product code: %u", rom->product_code)
DEBUG(" - version: %u", rom->version)
DEBUG(" - region code: %u (%s)", rom->region_code, region ? region : "unknown")
DEBUG(" - reported size: %s", parse_reported_size(header[0xF] & 0xF))
DEBUG(" - reported size: %s", parse_reported_size(size))
return true;
}

@@ -184,6 +217,7 @@ const char* rom_open(ROM **rom_ptr, const char *path)
rom->data = NULL;
rom->size = 0;
rom->checksum = 0;
rom->valid_checksum = false;
rom->product_code = 0;
rom->version = 0;
rom->region_code = 0;


+ 2
- 0
src/rom.h Visa fil

@@ -3,6 +3,7 @@

#pragma once

#include <stdbool.h>
#include <stdint.h>
#include <stdlib.h>

@@ -21,6 +22,7 @@ typedef struct {
uint8_t *data;
size_t size;
uint16_t checksum;
bool valid_checksum;
uint32_t product_code;
uint8_t version;
uint8_t region_code;


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