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https://github.com/pret/pokegold.git
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Rangi
90 lines
2.3 KiB
C
90 lines
2.3 KiB
C
#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <stdint.h>
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#include "common.h"
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// The Game Boy cartridge header stores a global checksum at 0x014E-0x014F
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#define GLOBALOFF 0x014E
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// ASCII "N64PS3" header
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#define N64PS3SIZE 6
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// N64PS3 + CRC
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#define HEADERSIZE (N64PS3SIZE + 2)
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// Checksum every half-bank
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#define CHECKSIZE 0x2000
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// The CRC polynomial value
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#define CRC_POLY 0xC387
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// The CRC initial value (also used for checksums)
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#define CRC_INIT 0xFEFE
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uint8_t n64ps3[N64PS3SIZE] = {'N', '6', '4', 'P', 'S', '3'};
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#define SET_U16BE(file, off, v) do { \
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file[(off) + 0] = (uint8_t)(((v) & 0xFF00) >> 8); \
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file[(off) + 1] = (uint8_t)(((v) & 0x00FF) >> 0); \
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} while (0)
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void calculate_checksums(uint8_t *file, int filesize) {
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int NUMCHECKS = filesize / CHECKSIZE;
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int DATASIZE = HEADERSIZE + NUMCHECKS * 2; // 2 bytes per checksum
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int ORIGIN = filesize - DATASIZE; // Stadium data goes at the end of the file
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// Initialize the CRC table
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uint16_t crc_table[256];
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for (int i = 0; i < 256; i++) {
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uint16_t c = i;
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uint16_t rem = 0;
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for (int y = 0; y < 8; y++) {
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rem = (rem >> 1) ^ ((rem ^ c) & 1 ? CRC_POLY : 0);
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c >>= 1;
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}
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crc_table[i] = rem;
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}
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// Clear the global checksum
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SET_U16BE(file, GLOBALOFF, 0);
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// Initialize the Stadium data (this should be free space anyway)
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memset(file + ORIGIN, 0, DATASIZE);
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memcpy(file + ORIGIN, n64ps3, N64PS3SIZE);
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// Calculate the half-bank checksums
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for (int i = 0; i < NUMCHECKS; i++) {
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uint16_t checksum = CRC_INIT;
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for (int j = 0; j < CHECKSIZE; j++) {
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checksum += file[i * CHECKSIZE + j];
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}
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SET_U16BE(file, ORIGIN + HEADERSIZE + i * 2, checksum);
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}
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// Calculate the CRC of the half-bank checksums
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uint16_t crc = CRC_INIT;
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for (int i = ORIGIN + HEADERSIZE; i < ORIGIN + DATASIZE; i++) {
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crc = (crc >> 8) ^ crc_table[(crc & 0xFF) ^ file[i]];
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}
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SET_U16BE(file, ORIGIN + HEADERSIZE - 2, crc);
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// Calculate the global checksum
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uint16_t globalsum = 0;
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for (int i = 0; i < filesize; i++) {
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globalsum += file[i];
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}
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SET_U16BE(file, GLOBALOFF, globalsum);
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}
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int main(int argc, char *argv[]) {
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if (argc != 2) {
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fprintf(stderr, "Usage: stadium romfile\n");
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exit(1);
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}
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char *filename = argv[1];
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int filesize;
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uint8_t *file = read_u8(filename, &filesize);
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calculate_checksums(file, filesize);
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write_u8(filename, file, filesize);
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return 0;
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}
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