forked from KolibriOS/kolibrios
204 lines
6.5 KiB
C
204 lines
6.5 KiB
C
/**
|
|
* Decode a Game Genie code into an M68000 address/data pair.
|
|
* The Game Genie code is made of the characters
|
|
* ABCDEFGHJKLMNPRSTVWXYZ0123456789 (notice the missing I, O, Q and U).
|
|
* Where A = 00000, B = 00001, C = 00010, ... , on to 9 = 11111.
|
|
*
|
|
* These come out to a very scrambled bit pattern like this:
|
|
* (SCRA-MBLE is just an example)
|
|
*
|
|
* S C R A - M B L E
|
|
* 01111 00010 01110 00000 01011 00001 01010 00100
|
|
* ijklm nopIJ KLMNO PABCD EFGHd efgha bcQRS TUVWX
|
|
*
|
|
* Our goal is to rearrange that to this:
|
|
*
|
|
* 0000 0101 1001 1100 0100 0100 : 1011 0000 0111 1000
|
|
* ABCD EFGH IJKL MNOP QRST UVWX : abcd efgh ijkl mnop
|
|
*
|
|
* which in Hexadecimal is 059C44:B078. Simple, huh? ;)
|
|
*
|
|
* So, then, we dutifully change memory location 059C44 to B078!
|
|
* (of course, that's handled by a different source file :)
|
|
*/
|
|
#include <stdio.h>
|
|
#include <string.h>
|
|
#include "decode.h"
|
|
|
|
static char genie_chars[] = "AaBbCcDdEeFfGgHhJjKkLlMmNnPpRrSsTtVvWwXxYyZz0O1I2233445566778899";
|
|
|
|
/**
|
|
* Decode a Game Genie Code.
|
|
* This function converts a Game Genie code to an address:data pair.
|
|
* The code is given as an 8-character string, like "BJX0SA1C". It need not
|
|
* be null terminated, since only the first 8 characters are taken. It is
|
|
* assumed that the code is already made of valid characters, i.e. there are no
|
|
* Q's, U's, or symbols. If such a character is
|
|
* encountered, the function will return with a warning on stderr.
|
|
*
|
|
* The resulting address:data pair is returned in the struct patch pointed to
|
|
* by result. If an error results, both the address and data will be set to -1.
|
|
*
|
|
* @param[in] code 8 character Game Genie code.
|
|
* @param[out] result The resulting address:data pair is returned in the struct
|
|
* patch pointed to by result. If an error results, both the address and data
|
|
* will be set to -1.
|
|
*/
|
|
void genie_decode(const char *code, struct patch *result)
|
|
{
|
|
int i = 0, n;
|
|
char* x;
|
|
|
|
for(; i < 8; ++i)
|
|
{
|
|
/* If strchr returns NULL, we were given a bad character */
|
|
if(!(x = strchr(genie_chars, code[i])))
|
|
{
|
|
result->addr = -1; result->data = -1;
|
|
return;
|
|
}
|
|
n = (x - genie_chars) >> 1;
|
|
/* Now, based on which character this is, fit it into the result */
|
|
switch(i)
|
|
{
|
|
case 0:
|
|
/* ____ ____ ____ ____ ____ ____ : ____ ____ ABCD E___ */
|
|
result->data |= n << 3;
|
|
break;
|
|
case 1:
|
|
/* ____ ____ DE__ ____ ____ ____ : ____ ____ ____ _ABC */
|
|
result->data |= n >> 2;
|
|
result->addr |= (n & 3) << 14;
|
|
break;
|
|
case 2:
|
|
/* ____ ____ __AB CDE_ ____ ____ : ____ ____ ____ ____ */
|
|
result->addr |= n << 9;
|
|
break;
|
|
case 3:
|
|
/* BCDE ____ ____ ___A ____ ____ : ____ ____ ____ ____ */
|
|
result->addr |= (n & 0xF) << 20 | (n >> 4) << 8;
|
|
break;
|
|
case 4:
|
|
/* ____ ABCD ____ ____ ____ ____ : ___E ____ ____ ____ */
|
|
result->data |= (n & 1) << 12;
|
|
result->addr |= (n >> 1) << 16;
|
|
break;
|
|
case 5:
|
|
/* ____ ____ ____ ____ ____ ____ : E___ ABCD ____ ____ */
|
|
result->data |= (n & 1) << 15 | (n >> 1) << 8;
|
|
break;
|
|
case 6:
|
|
/* ____ ____ ____ ____ CDE_ ____ : _AB_ ____ ____ ____ */
|
|
result->data |= (n >> 3) << 13;
|
|
result->addr |= (n & 7) << 5;
|
|
break;
|
|
case 7:
|
|
/* ____ ____ ____ ____ ___A BCDE : ____ ____ ____ ____ */
|
|
result->addr |= n;
|
|
break;
|
|
}
|
|
/* Go around again */
|
|
}
|
|
return;
|
|
}
|
|
|
|
/**
|
|
* "Decode" an address/data pair into a structure. This is for "012345:ABCD"
|
|
* type codes. You're more likely to find Genie codes circulating around, but
|
|
* there's a chance you could come on to one of these. Which is nice, since
|
|
* they're MUCH easier to implement ;) Once again, the input should be
|
|
* depunctuated already.
|
|
*
|
|
* @param[in] code 8 character Game Genie code.
|
|
* @param[out] result The resulting address:data pair is returned in the struct
|
|
* patch pointed to by result. If an error results, both the address and data
|
|
* will be set to -1.
|
|
*/
|
|
void hex_decode(const char *code, struct patch *result)
|
|
{
|
|
static char hex_chars[] = "00112233445566778899AaBbCcDdEeFf";
|
|
char *x;
|
|
int i;
|
|
/* 6 digits for address */
|
|
for(i = 0; i < 6; ++i)
|
|
{
|
|
if(!(x = strchr(hex_chars, code[i])))
|
|
{
|
|
result->addr = result->data = -1;
|
|
return;
|
|
}
|
|
result->addr = (result->addr << 4) | ((x - hex_chars) >> 1);
|
|
}
|
|
/* 4 digits for data */
|
|
for(i = 6; i < 10; ++i)
|
|
{
|
|
if(!(x = strchr(hex_chars, code[i])))
|
|
{
|
|
result->addr = result->data = -1;
|
|
return;
|
|
}
|
|
result->data = (result->data << 4) | ((x - hex_chars) >> 1);
|
|
}
|
|
}
|
|
|
|
/**
|
|
* THIS is the function you call from the MegaDrive or whatever. This figures
|
|
* out whether it's a genie or hex code, depunctuates it, and calls the proper
|
|
* decoder.
|
|
*
|
|
* @param[in] code Game Genie or hex code.
|
|
* @param[out] result The resulting address:data pair is returned in the struct
|
|
* patch pointed to by result. If an error results, both the address and data
|
|
* will be set to -1.
|
|
*/
|
|
void decode(const char *code, struct patch *result)
|
|
{
|
|
int len = strlen(code), i, j;
|
|
char code_to_pass[16], *x;
|
|
const char *ad, *da;
|
|
int adl, dal;
|
|
|
|
/* Initialize the result */
|
|
result->addr = result->data = 0;
|
|
|
|
/* If it's 9 chars long and the 5th is a hyphen, we have a Game Genie
|
|
* code. */
|
|
if(len == 9 && code[4] == '-')
|
|
{
|
|
/* Remove the hyphen and pass to genie_decode */
|
|
code_to_pass[0] = code[0];
|
|
code_to_pass[1] = code[1];
|
|
code_to_pass[2] = code[2];
|
|
code_to_pass[3] = code[3];
|
|
code_to_pass[4] = code[5];
|
|
code_to_pass[5] = code[6];
|
|
code_to_pass[6] = code[7];
|
|
code_to_pass[7] = code[8];
|
|
code_to_pass[8] = '\0';
|
|
genie_decode(code_to_pass, result);
|
|
return;
|
|
}
|
|
/* Otherwise, we assume it's a hex code.
|
|
* Find the colon so we know where address ends and data starts. If there's
|
|
* no colon, then we haven't a code at all! */
|
|
if(!(x = strchr(code, ':'))) goto bad_code;
|
|
ad = code; da = x + 1; adl = x - code; dal = len - adl - 1;
|
|
/* If a section is empty or too long, toss it */
|
|
if(adl == 0 || adl > 6 || dal == 0 || dal > 4) goto bad_code;
|
|
/* Pad the address with zeros, then fill it with the value */
|
|
for(i = 0; i < (6 - adl); ++i) code_to_pass[i] = '0';
|
|
for(j = 0; i < 6; ++i, ++j) code_to_pass[i] = ad[j];
|
|
/* Do the same for data */
|
|
for(i = 6; i < (10 - dal); ++i) code_to_pass[i] = '0';
|
|
for(j = 0; i < 10; ++i, ++j) code_to_pass[i] = da[j];
|
|
code_to_pass[10] = '\0';
|
|
/* Decode and goodbye */
|
|
hex_decode(code_to_pass, result);
|
|
return;
|
|
|
|
bad_code:
|
|
/* AGH! Invalid code! */
|
|
result->data = result->addr = -1;
|
|
return;
|
|
}
|