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/* advexe.c - adventure code executer */
/*
	Copyright (c) 1986, by David Michael Betz
	All rights reserved
*/

#include "advint.h"
#include "advdbs.h"

/* external variables */
extern char line[];
extern int nouns[],*adjectives[];

/* local variables */
int pc,opcode,p2,p3,sts;
int stack[STKSIZE],*sp,*fp,*top;
long rseed = 1L;

/* external routines */
extern long time();

/* execute - execute adventure code */
int execute(code)
  int code;
{
    /* setup initial program counter */
    if ((pc = code) == NIL)
	return (CHAIN);

    /* initialize */
    sp = fp = top = stack + STKSIZE;

    /* execute the code */
    for (sts = 0; sts == 0; )
	exe_one();

    return (sts);
}

/* exe_one - execute one instruction */
exe_one()
{
    /* get the opcode */
    opcode = getcbyte(pc); pc++;

    /* execute the instruction */
    switch (opcode) {
    case OP_CALL:
		*--sp = getboperand();
		*--sp = pc;
		*--sp = (int)(top - fp);
		fp = sp;
		pc = getafield(fp[fp[2]+3],A_CODE);
		break;
    case OP_SEND:
		*--sp = getboperand();
		*--sp = pc;
		*--sp = (int)(top - fp);
		fp = sp;
		if (p2 = fp[fp[2]+3])
		    p2 = getofield(p2,O_CLASS);
		else
		    p2 = fp[fp[2]+2];
		if (p2 && (p2 = getp(p2,fp[fp[2]+1]))) {
		    pc = getafield(p2,A_CODE);
		    break;
		}
		*sp = NIL;
		/* return NIL if there is no method for this message */
    case OP_RETURN:
		if (fp == top)
		    sts = CHAIN;
		else {
		    p2 = *sp;
		    sp = fp;
		    fp = top - *sp++;
		    pc = *sp++;
		    p3 = *sp++;
		    sp += p3;
		    *sp = p2;
		}
		break;
    case OP_TSPACE:
		sp -= getboperand();
		break;
    case OP_TMP:
		p2 = getboperand();
		*sp = fp[-p2-1];
		break;
    case OP_TSET:
		p2 = getboperand();
		fp[-p2-1] = *sp;
		break;
    case OP_ARG:
		p2 = getboperand();
		if (p2 >= fp[2])
		    error("too few arguments");
		*sp = fp[p2+3];
		break;
    case OP_ASET:
		p2 = getboperand();
		if (p2 >= fp[2])
		    error("too few arguments");
		fp[p2+3] = *sp;
		break;
    case OP_BRT:
		pc = (*sp ? getwoperand() : pc+2);
		break;
    case OP_BRF:
		pc = (*sp ? pc+2 : getwoperand());
		break;
    case OP_BR:
		pc = getwoperand();
		break;
    case OP_T:
		*sp = T;
		break;
    case OP_NIL:
		*sp = NIL;
		break;
    case OP_PUSH:
		*--sp = NIL;
		break;
    case OP_NOT:
		*sp = (*sp ? NIL : T);
		break;
    case OP_ADD:
		p2 = *sp++;
		*sp += p2;
		break;
    case OP_SUB:
		p2 = *sp++;
		*sp -= p2;
		break;
    case OP_MUL:
		p2 = *sp++;
		*sp *= p2;
		break;
    case OP_DIV:
		p2 = *sp++;
		*sp = (p2 == 0 ? 0 : *sp / p2);
		break;
    case OP_REM:
		p2 = *sp++;
		*sp = (p2 == 0 ? 0 : *sp % p2);
		break;
    case OP_BAND:
		p2 = *sp++;
		*sp &= p2;
		break;
    case OP_BOR:
		p2 = *sp++;
		*sp |= p2;
		break;
    case OP_BNOT:
		*sp = ~*sp;
		break;
    case OP_LT:
		p2 = *sp++;
		*sp = (*sp < p2 ? T : NIL);
		break;
    case OP_EQ:
		p2 = *sp++;
		*sp = (*sp == p2 ? T : NIL);
		break;
    case OP_GT:
		p2 = *sp++;
		*sp = (*sp > p2 ? T : NIL);
		break;
    case OP_LIT:
		*sp = getwoperand();
		break;
    case OP_SPLIT:
		*sp = getboperand();
		break;
    case OP_SNLIT:
		*sp = -getboperand();
		break;
    case OP_VAR:
		*sp = getvalue(getwoperand());
		break;
    case OP_SVAR:
		*sp = getvalue(getboperand());
		break;
    case OP_SET:
		setvalue(getwoperand(),*sp);
		break;
    case OP_SSET:
		setvalue(getboperand(),*sp);
		break;
    case OP_GETP:
		p2 = *sp++;
		*sp = getp(*sp,p2);
		break;
    case OP_SETP:
		p3 = *sp++;
		p2 = *sp++;
		*sp = setp(*sp,p2,p3);
		break;
    case OP_PRINT:
		print(*sp);
		break;
    case OP_PNUMBER:
    		pnumber(*sp);
    		break;
    case OP_PNOUN:
		show_noun(*sp);
		break;
    case OP_TERPRI:
		trm_chr('\n');
		break;
    case OP_FINISH:
		sts = FINISH;
		break;
    case OP_CHAIN:
		sts = CHAIN;
		break;
    case OP_ABORT:
		sts = ABORT;
		break;
    case OP_EXIT:
#ifdef MAC
		macpause();
#endif
		trm_done();
		exit();
		break;
    case OP_YORN:
		trm_get(line);
		*sp = (line[0] == 'Y' || line[0] == 'y' ? T : NIL);
    		break;
    case OP_CLASS:
		*sp = getofield(*sp,O_CLASS);
		break;
    case OP_MATCH:
		p2 = *sp++;
		*sp = (match(*sp,nouns[p2-1],adjectives[p2-1]) ? T : NIL);
		break;
    case OP_SAVE:
		*sp = db_save();
		break;
    case OP_RESTORE:
		*sp = db_restore();
		break;
    case OP_RESTART:
		*sp = db_restart();
		break;
    case OP_RAND:
		*sp = getrand(*sp);
		break;
    case OP_RNDMIZE:
		setrand(time(0L));
		*sp = NIL;
		break;
    default:
	    if (opcode >= OP_XVAR && opcode < OP_XSET)
		*sp = getvalue(opcode - OP_XVAR);
	    else if (opcode >= OP_XSET && opcode < OP_XPLIT)
		setvalue(opcode - OP_XSET,*sp);
	    else if (opcode >= OP_XPLIT && opcode < OP_XNLIT)
		*sp = opcode - OP_XPLIT;
	    else if (opcode >= OP_XNLIT && opcode < 256)
		*sp = OP_XNLIT - opcode;
	    else
		trm_str("Bad opcode\n");
	    break;
    }
}

/* getboperand - get data byte */
int getboperand()
{
    int data;
    data = getcbyte(pc); pc += 1;
    return (data);
}

/* getwoperand - get data word */
int getwoperand()
{
    int data;
    data = getcword(pc); pc += 2;
    return (data);
}

/* print - print a message */
print(msg)
  int msg;
{
    int ch;

    msg_open(msg);
    while (ch = msg_byte())
	trm_chr(ch);
}

/* pnumber - print a number */
pnumber(n)
  int n;
{
    char buf[10];

    sprintf(buf,"%d",n);
    trm_str(buf);
}

/* getrand - get a random number between 0 and n-1 */
int getrand(n)
  int n;
{
    long k1;

    /* make sure we don't get stuck at zero */
    if (rseed == 0L) rseed = 1L;

    /* algorithm taken from Dr. Dobbs Journal, November 1985, page 91 */
    k1 = rseed / 127773L;
    if ((rseed = 16807L * (rseed - k1 * 127773L) - k1 * 2836L) < 0L)
	rseed += 2147483647L;

    /* return a random number between 0 and n-1 */
    return ((int)(rseed % (long)n));
}

/* setrand - set the random number seed */
setrand(n)
  long n;
{
    rseed = n;
}
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