/* process.c - Interpreter loop and program control
* Copyright (c) 1995-1997 Stefan Jokisch
*
* This file is part of Frotz.
*
* Frotz 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.
*
* Frotz 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., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
*/
#include "frotz.h"
#ifdef DJGPP
#include "djfrotz.h"
#endif
zword zargs[8];
int zargc;
static int finished = 0;
static void __extended__ (void);
static void __illegal__ (void);
void (*op0_opcodes[0x10]) (void) = {
z_rtrue,
z_rfalse,
z_print,
z_print_ret,
z_nop,
z_save,
z_restore,
z_restart,
z_ret_popped,
z_catch,
z_quit,
z_new_line,
z_show_status,
z_verify,
__extended__,
z_piracy
};
void (*op1_opcodes[0x10]) (void) = {
z_jz,
z_get_sibling,
z_get_child,
z_get_parent,
z_get_prop_len,
z_inc,
z_dec,
z_print_addr,
z_call_s,
z_remove_obj,
z_print_obj,
z_ret,
z_jump,
z_print_paddr,
z_load,
z_call_n
};
void (*var_opcodes[0x40]) (void) = {
__illegal__,
z_je,
z_jl,
z_jg,
z_dec_chk,
z_inc_chk,
z_jin,
z_test,
z_or,
z_and,
z_test_attr,
z_set_attr,
z_clear_attr,
z_store,
z_insert_obj,
z_loadw,
z_loadb,
z_get_prop,
z_get_prop_addr,
z_get_next_prop,
z_add,
z_sub,
z_mul,
z_div,
z_mod,
z_call_s,
z_call_n,
z_set_colour,
z_throw,
__illegal__,
__illegal__,
__illegal__,
z_call_s,
z_storew,
z_storeb,
z_put_prop,
z_read,
z_print_char,
z_print_num,
z_random,
z_push,
z_pull,
z_split_window,
z_set_window,
z_call_s,
z_erase_window,
z_erase_line,
z_set_cursor,
z_get_cursor,
z_set_text_style,
z_buffer_mode,
z_output_stream,
z_input_stream,
z_sound_effect,
z_read_char,
z_scan_table,
z_not,
z_call_n,
z_call_n,
z_tokenise,
z_encode_text,
z_copy_table,
z_print_table,
z_check_arg_count
};
void (*ext_opcodes[0x1d]) (void) = {
z_save,
z_restore,
z_log_shift,
z_art_shift,
z_set_font,
z_draw_picture,
z_picture_data,
z_erase_picture,
z_set_margins,
z_save_undo,
z_restore_undo,
z_print_unicode,
z_check_unicode,
__illegal__,
__illegal__,
__illegal__,
z_move_window,
z_window_size,
z_window_style,
z_get_wind_prop,
z_scroll_window,
z_pop_stack,
z_read_mouse,
z_mouse_window,
z_push_stack,
z_put_wind_prop,
z_print_form,
z_make_menu,
z_picture_table
};
/*
* init_process
*
* Initialize process variables.
*
*/
void init_process (void)
{
finished = 0;
} /* init_process */
/*
* load_operand
*
* Load an operand, either a variable or a constant.
*
*/
static void load_operand (zbyte type)
{
zword value;
if (type & 2) { /* variable */
zbyte variable;
CODE_BYTE (variable)
if (variable == 0)
value = *sp++;
else if (variable < 16)
value = *(fp - variable);
else {
zword addr = h_globals + 2 * (variable - 16);
LOW_WORD (addr, value)
}
} else if (type & 1) { /* small constant */
zbyte bvalue;
CODE_BYTE (bvalue)
value = bvalue;
} else CODE_WORD (value) /* large constant */
zargs[zargc++] = value;
}/* load_operand */
/*
* load_all_operands
*
* Given the operand specifier byte, load all (up to four) operands
* for a VAR or EXT opcode.
*
*/
static void load_all_operands (zbyte specifier)
{
int i;
for (i = 6; i >= 0; i -= 2) {
zbyte type = (specifier >> i) & 0x03;
if (type == 3)
break;
load_operand (type);
}
}/* load_all_operands */
/*
* interpret
*
* Z-code interpreter main loop
*
*/
void interpret (void)
{
do {
zbyte opcode;
CODE_BYTE (opcode)
zargc = 0;
if (opcode < 0x80) { /* 2OP opcodes */
load_operand ((zbyte) (opcode & 0x40) ? 2 : 1);
load_operand ((zbyte) (opcode & 0x20) ? 2 : 1);
var_opcodes[opcode & 0x1f] ();
} else if (opcode < 0xb0) { /* 1OP opcodes */
load_operand ((zbyte) (opcode >> 4));
op1_opcodes[opcode & 0x0f] ();
} else if (opcode < 0xc0) { /* 0OP opcodes */
op0_opcodes[opcode - 0xb0] ();
} else { /* VAR opcodes */
zbyte specifier1;
zbyte specifier2;
if (opcode == 0xec || opcode == 0xfa) { /* opcodes 0xec */
CODE_BYTE (specifier1) /* and 0xfa are */
CODE_BYTE (specifier2) /* call opcodes */
load_all_operands (specifier1); /* with up to 8 */
load_all_operands (specifier2); /* arguments */
} else {
CODE_BYTE (specifier1)
load_all_operands (specifier1);
}
var_opcodes[opcode - 0xc0] ();
}
#if defined(DJGPP) && defined(SOUND_SUPPORT)
if (end_of_sound_flag)
end_of_sound ();
#endif
} while (finished == 0);
finished--;
}/* interpret */
/*
* call
*
* Call a subroutine. Save PC and FP then load new PC and initialise
* new stack frame. Note that the caller may legally provide less or
* more arguments than the function actually has. The call type "ct"
* can be 0 (z_call_s), 1 (z_call_n) or 2 (direct call).
*
*/
void call (zword routine, int argc, zword *args, int ct)
{
long pc;
zword value;
zbyte count;
int i;
if (sp - stack < 4)
runtime_error (ERR_STK_OVF);
GET_PC (pc)
*--sp = (zword) (pc >> 9);
*--sp = (zword) (pc & 0x1ff);
*--sp = (zword) (fp - stack - 1);
*--sp = (zword) (argc | (ct << (f_setup.save_quetzal ? 12 : 8)));
fp = sp;
frame_count++;
/* Calculate byte address of routine */
if (h_version <= V3)
pc = (long) routine << 1;
else if (h_version <= V5)
pc = (long) routine << 2;
else if (h_version <= V7)
pc = ((long) routine << 2) + ((long) h_functions_offset << 3);
else /* h_version == V8 */
pc = (long) routine << 3;
if (pc >= story_size)
runtime_error (ERR_ILL_CALL_ADDR);
SET_PC (pc)
/* Initialise local variables */
CODE_BYTE (count)
if (count > 15)
runtime_error (ERR_CALL_NON_RTN);
if (sp - stack < count)
runtime_error (ERR_STK_OVF);
if (f_setup.save_quetzal)
fp[0] |= (zword) count << 8; /* Save local var count for Quetzal. */
value = 0;
for (i = 0; i < count; i++) {
if (h_version <= V4) /* V1 to V4 games provide default */
CODE_WORD (value) /* values for all local variables */
*--sp = (zword) ((argc-- > 0) ? args[i] : value);
}
/* Start main loop for direct calls */
if (ct == 2)
interpret ();
}/* call */
/*
* ret
*
* Return from the current subroutine and restore the previous stack
* frame. The result may be stored (0), thrown away (1) or pushed on
* the stack (2). In the latter case a direct call has been finished
* and we must exit the interpreter loop.
*
*/
void ret (zword value)
{
long pc;
int ct;
if (sp > fp)
runtime_error (ERR_STK_UNDF);
sp = fp;
ct = *sp++ >> (f_setup.save_quetzal ? 12 : 8);
frame_count--;
fp = stack + 1 + *sp++;
pc = *sp++;
pc = ((long) *sp++ << 9) | pc;
SET_PC (pc)
/* Handle resulting value */
if (ct == 0)
store (value);
if (ct == 2)
*--sp = value;
/* Stop main loop for direct calls */
if (ct == 2)
finished++;
}/* ret */
/*
* branch
*
* Take a jump after an instruction based on the flag, either true or
* false. The branch can be short or long; it is encoded in one or two
* bytes respectively. When bit 7 of the first byte is set, the jump
* takes place if the flag is true; otherwise it is taken if the flag
* is false. When bit 6 of the first byte is set, the branch is short;
* otherwise it is long. The offset occupies the bottom 6 bits of the
* first byte plus all the bits in the second byte for long branches.
* Uniquely, an offset of 0 means return false, and an offset of 1 is
* return true.
*
*/
void branch (bool flag)
{
long pc;
zword offset;
zbyte specifier;
zbyte off1;
zbyte off2;
CODE_BYTE (specifier)
off1 = specifier & 0x3f;
if (!flag)
specifier ^= 0x80;
if (!(specifier & 0x40)) { /* it's a long branch */
if (off1 & 0x20) /* propagate sign bit */
off1 |= 0xc0;
CODE_BYTE (off2)
offset = (off1 << 8) | off2;
} else offset = off1; /* it's a short branch */
if (specifier & 0x80) {
if (offset > 1) { /* normal branch */
GET_PC (pc)
pc += (short) offset - 2;
SET_PC (pc)
} else ret (offset); /* special case, return 0 or 1 */
}
}/* branch */
/*
* store
*
* Store an operand, either as a variable or pushed on the stack.
*
*/
void store (zword value)
{
zbyte variable;
CODE_BYTE (variable)
if (variable == 0)
*--sp = value;
else if (variable < 16)
*(fp - variable) = value;
else {
zword addr = h_globals + 2 * (variable - 16);
SET_WORD (addr, value)
}
}/* store */
/*
* direct_call
*
* Call the interpreter loop directly. This is necessary when
*
* - a sound effect has been finished
* - a read instruction has timed out
* - a newline countdown has hit zero
*
* The interpreter returns the result value on the stack.
*
*/
int direct_call (zword addr)
{
zword saved_zargs[8];
int saved_zargc;
int i;
/* Calls to address 0 return false */
if (addr == 0)
return 0;
/* Save operands and operand count */
for (i = 0; i < 8; i++)
saved_zargs[i] = zargs[i];
saved_zargc = zargc;
/* Call routine directly */
call (addr, 0, 0, 2);
/* Restore operands and operand count */
for (i = 0; i < 8; i++)
zargs[i] = saved_zargs[i];
zargc = saved_zargc;
/* Resulting value lies on top of the stack */
return (short) *sp++;
}/* direct_call */
/*
* __extended__
*
* Load and execute an extended opcode.
*
*/
static void __extended__ (void)
{
zbyte opcode;
zbyte specifier;
CODE_BYTE (opcode)
CODE_BYTE (specifier)
load_all_operands (specifier);
if (opcode < 0x1d) /* extended opcodes from 0x1d on */
ext_opcodes[opcode] (); /* are reserved for future spec' */
}/* __extended__ */
/*
* __illegal__
*
* Exit game because an unknown opcode has been hit.
*
*/
static void __illegal__ (void)
{
runtime_error (ERR_ILL_OPCODE);
}/* __illegal__ */
/*
* z_catch, store the current stack frame for later use with z_throw.
*
* no zargs used
*
*/
void z_catch (void)
{
store (f_setup.save_quetzal ? frame_count : (zword) (fp - stack));
}/* z_catch */
/*
* z_throw, go back to the given stack frame and return the given value.
*
* zargs[0] = value to return
* zargs[1] = stack frame
*
*/
void z_throw (void)
{
if (f_setup.save_quetzal) {
if (zargs[1] > frame_count)
runtime_error (ERR_BAD_FRAME);
/* Unwind the stack a frame at a time. */
for (; frame_count > zargs[1]; --frame_count)
fp = stack + 1 + fp[1];
} else {
if (zargs[1] > STACK_SIZE)
runtime_error (ERR_BAD_FRAME);
fp = stack + zargs[1];
}
ret (zargs[0]);
}/* z_throw */
/*
* z_call_n, call a subroutine and discard its result.
*
* zargs[0] = packed address of subroutine
* zargs[1] = first argument (optional)
* ...
* zargs[7] = seventh argument (optional)
*
*/
void z_call_n (void)
{
if (zargs[0] != 0)
call (zargs[0], zargc - 1, zargs + 1, 1);
}/* z_call_n */
/*
* z_call_s, call a subroutine and store its result.
*
* zargs[0] = packed address of subroutine
* zargs[1] = first argument (optional)
* ...
* zargs[7] = seventh argument (optional)
*
*/
void z_call_s (void)
{
if (zargs[0] != 0)
call (zargs[0], zargc - 1, zargs + 1, 0);
else
store (0);
}/* z_call_s */
/*
* z_check_arg_count, branch if subroutine was called with >= n arg's.
*
* zargs[0] = number of arguments
*
*/
void z_check_arg_count (void)
{
if (fp == stack + STACK_SIZE)
branch (zargs[0] == 0);
else
branch (zargs[0] <= (*fp & 0xff));
}/* z_check_arg_count */
/*
* z_jump, jump unconditionally to the given address.
*
* zargs[0] = PC relative address
*
*/
void z_jump (void)
{
long pc;
GET_PC (pc)
pc += (short) zargs[0] - 2;
if (pc >= story_size)
runtime_error (ERR_ILL_JUMP_ADDR);
SET_PC (pc)
}/* z_jump */
/*
* z_nop, no operation.
*
* no zargs used
*
*/
void z_nop (void)
{
/* Do nothing */
}/* z_nop */
/*
* z_quit, stop game and exit interpreter.
*
* no zargs used
*
*/
void z_quit (void)
{
finished = 9999;
}/* z_quit */
/*
* z_ret, return from a subroutine with the given value.
*
* zargs[0] = value to return
*
*/
void z_ret (void)
{
ret (zargs[0]);
}/* z_ret */
/*
* z_ret_popped, return from a subroutine with a value popped off the stack.
*
* no zargs used
*
*/
void z_ret_popped (void)
{
ret (*sp++);
}/* z_ret_popped */
/*
* z_rfalse, return from a subroutine with false (0).
*
* no zargs used
*
*/
void z_rfalse (void)
{
ret (0);
}/* z_rfalse */
/*
* z_rtrue, return from a subroutine with true (1).
*
* no zargs used
*
*/
void z_rtrue (void)
{
ret (1);
}/* z_rtrue */