#include "emu.h"
#include "includes/pacman.h"


static UINT8 decrypt(int addr, UINT8 e)
{
	static const UINT8 swap_xor_table[6][9] =
	{
		{ 7,6,5,4,3,2,1,0, 0x00 },
		{ 7,6,3,4,5,2,1,0, 0x20 },
		{ 5,0,4,3,7,1,2,6, 0xa4 },
		{ 5,0,4,3,7,1,2,6, 0x8c },
		{ 2,3,1,7,4,6,0,5, 0x6e },
		{ 2,3,4,7,1,6,0,5, 0x4e }
	};
	static const int picktable[32] =
	{
		0,2,4,4,4,2,0,2,2,0,2,4,4,2,0,2,
		5,3,5,1,5,3,5,3,1,5,1,5,5,3,5,3
	};
	UINT32 method = 0;
	const UINT8 *tbl;


	/* pick method from bits 0 2 5 7 9 of the address */
	method = picktable[
		(addr & 0x001) |
		((addr & 0x004) >> 1) |
		((addr & 0x020) >> 3) |
		((addr & 0x080) >> 4) |
		((addr & 0x200) >> 5)];

	/* switch method if bit 11 of the address is set */
	if ((addr & 0x800) == 0x800)
		method ^= 1;

	tbl = swap_xor_table[method];
	return BITSWAP8(e,tbl[0],tbl[1],tbl[2],tbl[3],tbl[4],tbl[5],tbl[6],tbl[7]) ^ tbl[8];
}


void jumpshot_decode(running_machine &machine)
{
	int i;
	UINT8 *RAM;

	/* CPU ROMs */

	RAM = machine.root_device().memregion("maincpu")->base();
	for (i = 0; i < 0x4000; i++)
	{
		RAM[i] = decrypt(i,RAM[i]);
	}
}


