SynacorVM

synacorvm.c

#include <stdio.h>
#include <stdlib.h>

#define eval(v) (v < 32768u ? v : memory[v])

static int pc, sp;
static unsigned short stack[1024];
static unsigned short memory[(1ul << 15) + 8];

static int
step(void)
{
    int in;
    unsigned a, b, c, op = memory[pc++];
    switch (op) {
        case  0: return 0;
        case  1: a = memory[pc++];
                 b = memory[pc++];
                 memory[a] = eval(b);
                 return 1;
        case  2: a = memory[pc++];
                 stack[sp++] = eval(a);
                 return 1;
        case  3: if (!sp) abort();
                 a = memory[pc++];
                 memory[a] = stack[--sp];
                 return 1;
        case  4: a = memory[pc++];
                 b = memory[pc++];
                 c = memory[pc++];
                 memory[a] = eval(b) == eval(c);
                 return 1;
        case  5: a = memory[pc++];
                 b = memory[pc++];
                 c = memory[pc++];
                 memory[a] = eval(b) > eval(c);
                 return 1;
        case  6: a = memory[pc];
                 pc = eval(a);
                 return 1;
        case  7: a = memory[pc++];
                 b = memory[pc++];
                 if (eval(a)) pc = eval(b);
                 return 1;
        case  8: a = memory[pc++];
                 b = memory[pc++];
                 if (!eval(a)) pc = eval(b);
                 return 1;
        case  9: a = memory[pc++];
                 b = memory[pc++];
                 c = memory[pc++];
                 memory[a] = (eval(b) + eval(c)) % 32768u;
                 return 1;
        case 10: a = memory[pc++];
                 b = memory[pc++];
                 c = memory[pc++];
                 memory[a] = (eval(b) * eval(c)) % 32768u;
                 return 1;
        case 11: a = memory[pc++];
                 b = memory[pc++];
                 c = memory[pc++];
                 memory[a] = eval(b) % eval(c);
                 return 1;
        case 12: a = memory[pc++];
                 b = memory[pc++];
                 c = memory[pc++];
                 memory[a] = eval(b) & eval(c);
                 return 1;
        case 13: a = memory[pc++];
                 b = memory[pc++];
                 c = memory[pc++];
                 memory[a] = eval(b) | eval(c);
                 return 1;
        case 14: a = memory[pc++];
                 b = memory[pc++];
                 memory[a] = ~eval(b) & 0x7fff;
                 return 1;
        case 15: a = memory[pc++];
                 b = memory[pc++];
                 memory[a] = memory[eval(b)];
                 return 1;
        case 16: a = memory[pc++];
                 b = memory[pc++];
                 memory[eval(a)] = eval(b);
                 return 1;
        case 17: a = memory[pc++];
                 stack[sp++] = pc;
                 pc = eval(a);
                 return 1;
        case 18: if (!sp) return 0;
                 pc = stack[--sp];
                 return 1;
        case 19: a = memory[pc++];
                 putchar(eval(a));
                 return 1;
        case 20: in = getchar();
                 if (in == EOF) abort();
                 memory[memory[pc++]] = in;
                 return 1;
        case 21: return 1;
    }
    abort();
}

int
main(int argc, char *argv[])
{
    FILE *f = fopen(argv[argc - 1], "rb");
    int i = 0;
    for (;;) {
        unsigned v;
        int lo = fgetc(f);
        int hi = fgetc(f);
        if (lo == EOF) break;
        if (hi == EOF) abort();
        v = (unsigned)hi << 8 | lo;
        if (v > 32775) abort();
        memory[i++] = v;
    }
    fclose(f);

    while (step())
        ;
    return 0;
}