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Added correct decryption function which doesn't rely on the second half of the rom as an inverted key. The actual decryption on hardware is likely done by an undumped PAL which also handles memory mapping. [Lord Nightmare, Kevtris]

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This commit is contained in:
Jonathan Gevaryahu 2011-04-07 06:08:06 +00:00
parent 302b6ed34d
commit a794f925dd
1 changed files with 11 additions and 2 deletions
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13
src/mame/drivers/3super8.c
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@ -165,9 +165,18 @@ static DRIVER_INIT( 3super8 )
UINT8 *ROM = machine.region("maincpu")->base();
int i;
/* TODO: proper decryption scheme */
/* Decryption is probably done using one macrocell/output on an address decoding pal which we do not have a dump of */
/* The encryption is quite awful actually, especially since the program rom is entirely blank/0xFF but encrypted on its second half, exposing the entire function in plaintext */
/* Input: A6, A7, A8, A9, A11; Output: D5 XOR */
/* function: (A6&A8)&((!A7&A11)|(A9&!A11)); */
/* nor-reduced: !(!(!(!A6|!A8))|!(!(A7|!A11)|!(!A9|A11))); */
for(i=0;i<0x10000;i++)
ROM[i] ^= (ROM[i+0x10000] ^ 0xff);
{
UINT8 a6, a7, a8, a9, a11, d5 = 0;
a6 = BIT(i,6); a7 = BIT(i,7); a8 = BIT(i,8); a9 = BIT(i,9); a11 = BIT(i,11);
d5 = (a6&a8)&((!a7&a11)|(a9&!a11));
ROM[i] ^= d5*0x20;
}
}
GAME( 199?, 3super8, 0, 3super8, 3super8, 3super8, ROT0, "<unknown>", "3 Super 8 (Italy)", GAME_NOT_WORKING|GAME_NO_SOUND )