/***********************************
	ilo-plan9.c (C) Jim Taylor
	
	Example compilation (amd64):	
	6c ilo-plan9.c
	6l -o ilo ilo-plan9.6
	
	May want to run it with vt.
***********************************/

#include <u.h>
#include <libc.h>

#define T ds[sp]	/* Top of Data Stack    */
#define N ds[sp-1]	/* Next on Data Stack   */
#define R as[rp]	/* Top of Address Stack */
#define INST(c_name); void c_name(void)		/* Shorthand for VM INSTructions */

int ip,        /* instruction pointer             */
	sp,        /* data stack pointer              */
	rp,        /* address stack pointer           */
	ds[33],    /* data stack                      */
	as[257],   /* address stack                   */
	m[65536];  /* memory                          */

char *blocks,   /* name of block file (ilo.blocks) */
	*rom;      /* name of image (ilo.rom)         */

int a, b, fd, s, d, l;
char i[1];

void 
push(int v) 
{ 
	ds[sp+1] = v; 
	sp += 1; 
}

int 
pop(void) 
{ 
	sp -= 1; 
	return ds[sp+1]; 
}

void 
load_image(void) 
{
	fd = open(rom, OREAD);
	if(!fd)
		return;
	read(fd, &m, 65536*4);
	close(fd);
	ip = sp = rp = 0;
}

void 
save_image(void) 
{
	fd = open(rom, OWRITE);
	write(fd, &m, 65536*4);
	close(fd);
}

void 
block_common(void) 
{
	b = pop(); /* block buffer */
	a = pop(); /* block number */
	seek(fd, 4096*a, 0);
}

void 
read_block(void) 
{
	fd = open(blocks, OREAD);
	block_common();
	read(fd, m+b, 4096);
	close(fd);
}

void 
write_block(void) 
{
	fd = open(blocks, OWRITE);
	block_common();
	write(fd, m+b, 4096);
	close(fd);
}

void save_ip(void) { rp += 1; R = ip; }
void symmetric(void) { if (b >= 0 && N < 0) { T += 1; N -= b; } }

INST(li) { ip += 1; push(m[ip]); }
INST(du) { push(T); }
INST(dr) { ds[sp] = 0; sp -= 1; }
INST(sw) { a = T; T = N; N = a; }
INST(pu) { rp += 1; R = pop(); }
INST(po) { push(R); rp -= 1; }
INST(ju) { ip = pop() - 1; }
INST(ca) { save_ip(); ip = pop() - 1; }
INST(cc) { a = pop(); if (pop()) { save_ip(); ip = a - 1; } }
INST(cj) { a = pop(); if (pop()) { ip = a - 1; } }
INST(re) { ip = R; rp -= 1; }
INST(eq) { N = (N == T) ? -1 : 0; sp -= 1; }
INST(ne) { N = (N != T) ? -1 : 0; sp -= 1; }
INST(lt) { N = (N <  T) ? -1 : 0; sp -= 1; }
INST(gt) { N = (N >  T) ? -1 : 0; sp -= 1; }
INST(fe) { T = m[T]; }
INST(st) { m[T] = N; sp -= 2; }
INST(ad) { N += T; sp -= 1; }
INST(su) { N -= T; sp -= 1; }
INST(mu) { N *= T; sp -= 1; }
INST(di) { a = T; b = N; T = b / a; N = b % a; symmetric(); }
INST(an) { N = T & N; sp -= 1; }
INST(or) { N = T | N; sp -= 1; }
INST(xo) { N = T ^ N; sp -= 1; }
INST(sl) { N = N << T; sp -= 1; }
INST(sr) { N = N >> T; sp -= 1; }
INST(cp)
{
	l = pop(); d = pop(); 
	s = T; T = -1;
	while(l) { 
		if (m[d] != m[s]) 
			T = 0;
		l -= 1; s += 1; d += 1; 
	} 
}
INST(cy)
{
	l = pop(); d = pop(); s = pop();
	while(l) { 
		m[d] = m[s]; l -= 1; s += 1; d += 1; 
	} 
}
INST(ioa) { i[0] = (char)pop(); write(1, &i, 1); }
INST(iob) { read(0, &i, 1); push(i[0]); }
INST(ioc) { read_block(); }
INST(iod) { write_block(); }
INST(ioe) { save_image(); }
INST(iof) { load_image(); ip = -1; }
INST(iog) { ip = 65536; }
INST(ioh) { push(sp); push(rp); }
INST(io)
{
	switch (pop()) {
		case 0: ioa(); break;  case 1: iob(); break;
		case 2: ioc(); break;  case 3: iod(); break;
		case 4: ioe(); break;  case 5: iof(); break;
		case 6: iog(); break;  case 7: ioh(); break;
		default: break;
	}
}

void 
process(int o) 
{
	switch (o) {
		case  0:       break;   case  1: li(); break;
		case  2: du(); break;   case  3: dr(); break;
		case  4: sw(); break;   case  5: pu(); break;
		case  6: po(); break;   case  7: ju(); break;
		case  8: ca(); break;   case  9: cc(); break;
		case 10: cj(); break;   case 11: re(); break;
		case 12: eq(); break;   case 13: ne(); break;
		case 14: lt(); break;   case 15: gt(); break;
		case 16: fe(); break;   case 17: st(); break;
		case 18: ad(); break;   case 19: su(); break;
		case 20: mu(); break;   case 21: di(); break;
		case 22: an(); break;   case 23: or(); break;
		case 24: xo(); break;   case 25: sl(); break;
		case 26: sr(); break;   case 27: cp(); break;
		case 28: cy(); break;   case 29: io(); break;
		default: break;
	}
}

void 
process_bundle(int opcode) 
{
	process(opcode & 0xFF);
	process((opcode >> 8) & 0xFF);
	process((opcode >> 16) & 0xFF);
	process((opcode >> 24) & 0xFF);
}

void 
execute(void) 
{
	while(ip < 65536) {
		process_bundle(m[ip]);
		ip += 1;
	}
}

void
main() 
{
	blocks = "ilo.blocks";
	rom = "ilo.rom";
	load_image();
	execute();
	exits(nil);
}