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#include "drain.h"
#include "ops.h"
#include <stdio.h>
#include <stdint.h>
#define MEM_SIZE 0xffff
static uint16_t *mem = NULL, *stack = NULL, *rstack = NULL;
static size_t stack_ptr = 0, rstack_ptr = 0;
static int
fail(void)
{
if (mem != NULL)
free(mem);
if (stack != NULL)
free(stack);
if (rstack != NULL)
free(rstack);
return 1;
}
static uint16_t
get_short(const unsigned char *s)
{
return s[0] | (s[1] * 0x0100);
}
static void
push(uint16_t v)
{
stack[stack_ptr] = v;
stack_ptr += 1;
if (stack_ptr >= MEM_SIZE) {
fprintf(stderr, "stack overflow\n");
exit(fail());
}
}
static uint16_t
pop(void)
{
if (stack_ptr == 0) {
fprintf(stderr, "stack underflow\n");
exit(fail());
}
stack_ptr -= 1;
return stack[stack_ptr];
}
static void
push_rs(uint16_t v)
{
rstack[rstack_ptr] = v;
rstack_ptr += 1;
if (rstack_ptr >= MEM_SIZE) {
fprintf(stderr, "return stack overflow\n");
exit(fail());
}
}
static uint16_t
pop_rs(void)
{
if (rstack_ptr == 0) {
fprintf(stderr, "return stack underflow\n");
exit(fail());
}
rstack_ptr -= 1;
return rstack[rstack_ptr];
}
static void
exec_data(uint16_t *mem)
{
for (long pc = 0; pc < MEM_SIZE;) {
switch (mem[pc]) {
case OP_NOP:
break;
case OP_LIT:
push(mem[pc + 1]);
pc += 1;
break;
case OP_POP:
pop();
break;
case OP_NIP: {
const uint16_t a = pop();
pop();
push(a);
} break;
case OP_SWP: {
const uint16_t a = pop();
const uint16_t b = pop();
push(a);
push(b);
} break;
case OP_DUP: {
const uint16_t a = pop();
push(a);
push(a);
} break;
case OP_ADD:
push(pop() + pop());
break;
case OP_WRT:
putchar(pop());
break;
case OP_JNZ:
if (pop() != 0) {
pc = mem[pc + 1];
continue;
}
pc += 1;
break;
case OP_JRT:
push_rs(pc);
pc = mem[pc + 1];
continue;
case OP_RET:
if (rstack_ptr > 0) {
pc = pop_rs() + 1;
break;
}
return;
case OP_LDA:
push(mem[pop()]);
break;
case OP_STA: {
const uint16_t a = pop();
const uint16_t b = pop();
mem[a] = b;
} break;
default:
fprintf(stderr, "unhandled opcode %04x\n", mem[pc]);
if (mem[pc] <= OP_SLP)
fprintf(stderr, "(%s)\n", ops[mem[pc]]);
exit(fail());
}
pc += 1;
}
}
int
main(int argc, char **argv)
{
if (argc != 2) {
fprintf(stderr, "usage: %s <rom>\n", argv[0]);
return 1;
}
FILE *file = fopen(argv[1], "rb");
if (file == NULL) {
perror(argv[1]);
return 1;
}
long size;
unsigned char *const data = (unsigned char*)drain(file, &size);
fclose(file);
if (data == NULL)
return 1;
mem = calloc(MEM_SIZE, sizeof(uint16_t));
if (mem == NULL) {
perror("main:calloc");
free(data);
return 1;
}
for (long i = 0; i < size; i += 2)
mem[i / 2] = get_short(data + i);
free(data);
stack = calloc(MEM_SIZE, sizeof(uint16_t));
if (stack == NULL) {
perror("main:calloc");
return fail();
}
rstack = calloc(MEM_SIZE, sizeof(uint16_t));
if (rstack == NULL) {
perror("main:calloc");
return fail();
}
exec_data(mem);
return fail(), 0;
}
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