/* z80.c: z80 supplementary functions
   Copyright (c) 1999-2003 Philip Kendall

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License along
   with this program; if not, write to the Free Software Foundation, Inc.,
   51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.

   Author contact information:

   E-mail: philip-fuse@shadowmagic.org.uk

*/

#include "z80.h"
#include "z80_macros.h"

void (*z80_writebyte)(uint16, uint8);
uint8 (*z80_readbyte)(uint16);
void (*z80_writeport)(uint16, uint8);
uint8 (*z80_readport)(uint16);

/* Whether a half carry occurred or not can be determined by looking at
   the 3rd bit of the two arguments and the result; these are hashed
   into this table in the form r12, where r is the 3rd bit of the
   result, 1 is the 3rd bit of the 1st argument and 2 is the
   third bit of the 2nd argument; the tables differ for add and subtract
   operations */
const uint8 halfcarry_add_table[] =
	{0, FLAG_H, FLAG_H, FLAG_H, 0, 0, 0, FLAG_H};
const uint8 halfcarry_sub_table[] =
	{0, 0, FLAG_H, 0, FLAG_H, 0, FLAG_H, FLAG_H};

/* Similarly, overflow can be determined by looking at the 7th bits; again
   the hash into this table is r12 */
const uint8 overflow_add_table[] = {0, 0, 0, FLAG_V, FLAG_V, 0, 0, 0};
const uint8 overflow_sub_table[] = {0, FLAG_V, 0, 0, 0, 0, FLAG_V, 0};

/* Some more tables; initialised in z80_init_tables() */

uint8 sz53_table[0x100];   /* The S, Z, 5 and 3 bits of the index */
uint8 parity_table[0x100]; /* The parity of the lookup value */
uint8 sz53p_table[0x100];  /* OR the above two tables together */

/* This is what everything acts on! */
processor z80;
uint64 z80_tstates;
uint64 last_z80_tstates;

static void z80_init_tables(void);

/* Set up the z80 emulation */
void z80_init(void)
{
	z80_init_tables();
}

/* Initalise the tables used to set flags */
static void z80_init_tables(void)
{
	int i, j, k;
	uint8 parity;

	for (i = 0; i < 0x100; i++)
	{
		sz53_table[i] = i & (FLAG_3 | FLAG_5 | FLAG_S);
		j = i;
		parity = 0;
		for (k = 0; k < 8; k++)
		{
			parity ^= j & 1;
			j >>= 1;
		}
		parity_table[i] = (parity ? 0 : FLAG_P);
		sz53p_table[i] = sz53_table[i] | parity_table[i];
	}

	sz53_table[0] |= FLAG_Z;
	sz53p_table[0] |= FLAG_Z;
}

/* Reset the z80 */
void z80_reset(void)
{
	AF = BC = DE = HL = 0;
	AF_ = BC_ = DE_ = HL_ = 0;
	IX = IY = 0;
	I = R = R7 = 0;
	SP = PC = 0;
	IFF1 = IFF2 = IM = 0;
	z80.halted = 0;

	z80.interrupts_enabled_at = 0;
	z80_tstates = last_z80_tstates = 0;
}

/* Process a z80 maskable interrupt */
int z80_interrupt(void)
{

	if (IFF1)
	{

		/* If interrupts have just been enabled, don't accept the interrupt now,
       but check after the next instruction has been executed */
		if (z80_tstates == z80.interrupts_enabled_at)
		{
			return 0;
		}

		if (z80.halted)
		{
			PC++;
			z80.halted = 0;
		}

		IFF1 = IFF2 = 0;

		Z80_WB_MACRO(--SP, PCH);
		Z80_WB_MACRO(--SP, PCL);

		R++;

		switch (IM)
		{
		case 0:
			PC = 0x0038;
			z80_tstates += 7;
			break;
		case 1:
			PC = 0x0038;
			z80_tstates += 7;
			break;
		case 2:
		{
			uint16 inttemp = (0x100 * I) + 0xff;
			PCL = Z80_RB_MACRO(inttemp++);
			PCH = Z80_RB_MACRO(inttemp);
			z80_tstates += 7;
			break;
		}
			//default:
			//	ui_error( UI_ERROR_ERROR, "Unknown interrupt mode %d", IM );
			//	fuse_abort();
		}

		return 1; /* Accepted an interrupt */
	}
	else
	{
		return 0; /* Did not accept an interrupt */
	}
}

/* Process a z80 non-maskable interrupt */
void z80_nmi(void)
{
	if (z80.halted)
	{
		PC++;
		z80.halted = 0;
	}

	IFF1 = 0;

	Z80_WB_MACRO(--SP, PCH);
	Z80_WB_MACRO(--SP, PCL);

	/* FIXME: how is R affected? */

	/* FIXME: how does contention apply here? */
	z80_tstates += 11;
	PC = 0x0066;
}