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control.c
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control.c
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/*
* control.c
*
* Functions that alter the flow of control.
*
*/
#include "ztypes.h"
static const char *v1_lookup_table[3] = {
"abcdefghijklmnopqrstuvwxyz",
"ABCDEFGHIJKLMNOPQRSTUVWXYZ",
" 0123456789.,!?_#'\"/\\<-:()"
};
static const char *v3_lookup_table[3] = {
"abcdefghijklmnopqrstuvwxyz",
"ABCDEFGHIJKLMNOPQRSTUVWXYZ",
" \n0123456789.,!?_#'\"/\\-:()"
};
/*
* check_argument
*
* Jump if argument is present.
*
*/
#ifdef __STDC__
void check_argument (zword_t argc)
#else
void check_argument (argc)
zword_t argc;
#endif
{
conditional_jump (argc <= (zword_t) (stack[fp + 1] & ARGS_MASK));
}/* check_argument */
/*
* call
*
* Call a subroutine. Save PC and FP then load new PC and initialise stack based
* local arguments.
*
*/
#ifdef __STDC__
int call (int argc, zword_t *argv, int type)
#else
int call (argc, argv, type)
int argc;
zword_t *argv;
int type;
#endif
{
zword_t arg;
int i = 1, args, status = 0;
/* Convert calls to 0 as returning FALSE */
if (argv[0] == 0) {
if (type == FUNCTION)
store_operand (FALSE);
return (0);
}
/* Save current PC, FP and argument count on stack */
stack[--sp] = (zword_t) (pc / PAGE_SIZE);
stack[--sp] = (zword_t) (pc % PAGE_SIZE);
stack[--sp] = fp;
stack[--sp] = (argc - 1) | type;
/* Create FP for new subroutine and load new PC */
fp = sp - 1;
pc = (unsigned long) argv[0] * story_scaler;
/* Read argument count and initialise local variables */
args = (unsigned int) read_code_byte ();
while (--args >= 0) {
arg = (h_type > V4) ? 0 : read_code_word ();
stack[--sp] = (--argc > 0) ? argv[i++] : arg;
}
/* If the call is asynchronous then call the interpreter directly.
We will return back here when the corresponding return frame is
encountered in the ret call. */
if (type == ASYNC) {
status = interpret ();
interpreter_state = RUN;
interpreter_status = 1;
}
return (status);
}/* call */
/*
* ret
*
* Return from subroutine. Restore FP and PC from stack.
*
*/
#ifdef __STDC__
void ret (zword_t value)
#else
void ret (value)
zword_t value;
#endif
{
zword_t argc;
/* Clean stack */
sp = fp + 1;
/* Restore argument count, FP and PC */
argc = stack[sp++];
fp = stack[sp++];
pc = stack[sp++];
pc += (unsigned long) stack[sp++] * PAGE_SIZE;
/* If this was an async call then stop the interpreter and return
the value from the async routine. This is slightly hacky using
a global state variable, but ret can be called with conditional_jump
which in turn can be called from all over the place, sigh. A
better design would have all opcodes returning the status RUN, but
this is too much work and makes the interpreter loop look ugly */
if ((argc & TYPE_MASK) == ASYNC) {
interpreter_state = STOP;
interpreter_status = (int) value;
} else {
/* Return subroutine value for function call only */
if ((argc & TYPE_MASK) == FUNCTION)
store_operand (value);
}
}/* ret */
/*
* jump
*
* Unconditional jump. Jump is PC relative.
*
*/
#ifdef __STDC__
void jump (zword_t offset)
#else
void jump (offset)
zword_t offset;
#endif
{
pc = (unsigned long) (pc + (short) offset - 2);
}/* jump */
/*
* restart
*
* Restart game by initialising environment and reloading start PC.
*
*/
#ifdef __STDC__
void restart (void)
#else
void restart ()
#endif
{
unsigned int i, j, restart_size, scripting_flag;
/* Reset output buffer */
flush_buffer (TRUE);
/* Reset text control flags */
formatting = ON;
outputting = ON;
redirecting = OFF;
scripting_disable = OFF;
/* Randomise */
srand ((unsigned int) time (NULL));
/* Remember scripting state */
scripting_flag = get_word (H_FLAGS) & SCRIPTING_FLAG;
/* Load restart size and reload writeable data area */
restart_size = (h_restart_size / PAGE_SIZE) + 1;
for (i = 0; i < restart_size; i++)
read_page (i, &datap[i * PAGE_SIZE]);
/* Restart the screen */
set_status_size (0);
set_attribute (NORMAL);
erase_window (SCREEN);
restart_screen ();
/* Reset the interpreter state */
if (scripting_flag)
set_word (H_FLAGS, (get_word (H_FLAGS) | SCRIPTING_FLAG));
set_byte (H_INTERPRETER, h_interpreter);
set_byte (H_INTERPRETER_VERSION, h_interpreter_version);
set_byte (H_SCREEN_ROWS, screen_rows); /* Screen dimension in characters */
set_byte (H_SCREEN_COLUMNS, screen_cols);
set_byte (H_SCREEN_LEFT, 0); /* Screen dimension in smallest addressable units, ie. pixels */
set_byte (H_SCREEN_RIGHT, screen_cols);
set_byte (H_SCREEN_TOP, 0);
set_byte (H_SCREEN_BOTTOM, screen_rows);
set_byte (H_MAX_CHAR_WIDTH, 1); /* Size of a character in screen units */
set_byte (H_MAX_CHAR_HEIGHT, 1);
/* Initialise status region */
if (h_type < V4) {
set_status_size (0);
blank_status_line ();
}
/* Initialise the character translation lookup tables */
for (i = 0; i < 3; i++) {
for (j = 0; j < 26; j++) {
if (h_alternate_alphabet_offset) {
lookup_table[i][j] = get_byte (h_alternate_alphabet_offset + (i * 26) + j);
} else {
if (h_type == V1)
lookup_table[i][j] = v1_lookup_table[i][j];
else
lookup_table[i][j] = v3_lookup_table[i][j];
}
}
}
/* Load start PC, SP and FP */
pc = h_start_pc;
sp = STACK_SIZE;
fp = STACK_SIZE - 1;
}/* restart */
/*
* get_fp
*
* Return the value of the frame pointer (FP) for later use with unwind.
* Before V5 games this was a simple pop.
*
*/
#ifdef __STDC__
void get_fp (void)
#else
void get_fp ()
#endif
{
if (h_type > V4)
store_operand (fp);
else
sp++;
}/* get_fp */
/*
* unwind
*
* Remove one or more stack frames and return. Works like longjmp, see get_fp.
*
*/
#ifdef __STDC__
void unwind (zword_t value, zword_t new_fp)
#else
void unwind (value, new_fp)
zword_t value;
zword_t new_fp;
#endif
{
if (new_fp > fp)
fatal ("Bad frame for unwind");
fp = new_fp;
ret (value);
}/* unwind */