#include "driver.h"
#include "vidhrdw/generic.h"


static unsigned char decrypt(int addr, unsigned char e)
{
	static const unsigned char swap_xor_table[6][9] =
	{
		{ 7,6,5,4,3,2,1,0, 0x00 },
		{ 7,6,5,4,3,2,1,0, 0x28 },
		{ 6,1,3,2,5,7,0,4, 0x96 },
		{ 6,1,5,2,3,7,0,4, 0xbe },
		{ 0,3,7,6,4,2,1,5, 0xd5 },
		{ 0,3,4,6,7,2,1,5, 0xdd }
	};
	static const int picktable[32] =
	{
		0,2,4,2,4,0,4,2,2,0,2,2,4,0,4,2,
		2,2,4,0,4,2,4,0,0,4,0,4,4,2,4,2
	};
	unsigned int method = 0;
	const unsigned char *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 pacplus_decode(void)
{
	int i;
	unsigned char *RAM;

	/* CPU ROMs */

	RAM = memory_region(REGION_CPU1);
	for (i = 0; i < 0x4000; i++)
	{
		RAM[i] = decrypt(i,RAM[i]);
	}
}


