opcodes.c

#include <glib.h>

typedef struct {
    GSList *stack;
} MachineState;
static void machine_push (MachineState *state, int v);
static int  machine_pop  (MachineState *state);

/* pushes an operand onto the operand stack */
static void
op_pushint (MachineState *state,
            int           v)
{
    machine_push (state, v);
}

static void
op_add (MachineState *state)
{
    int a, b, res;
    a = machine_pop (state);
    b = machine_pop (state);
    res = a + b;
    machine_push (state, res);
}

static void
op_sub (MachineState *state)
{
    int a, b, res;
    a = machine_pop (state);
    b = machine_pop (state);
    res = a - b;
    machine_push (state, res);
}

static void
op_mul (MachineState *state)
{
    int a, b, res;
    a = machine_pop (state);
    b = machine_pop (state);
    res = a * b;
    machine_push (state, res);
}

G_GNUC_UNUSED
static void
op_pop (MachineState *state)
{
    machine_pop (state);
}

G_GNUC_UNUSED
static void
op_dup (MachineState *state)
{
    int a;
    a = machine_pop (state);
    machine_push (state, a);
    machine_push (state, a);
}

static void
op_swap (MachineState *state)
{
    int a, b;
    a = machine_pop (state);
    b = machine_pop (state);
    machine_push (state, a);
    machine_push (state, b);
}

static void
op_print (MachineState *state)
{
    int a;
    a = machine_pop (state);
    g_print ("%d\n", a);
}

int
main (int argc, char **argv)
{
    MachineState state;
    state.stack = NULL;

    /* (5 * (2 + 4)) - 3 */

    op_pushint (&state, 5);

    op_pushint (&state, 2);
    op_pushint (&state, 4);
    op_add (&state);

    op_mul (&state);

    op_pushint (&state, 3);
    op_swap (&state);
    op_sub (&state);

    op_print (&state);

    return 0;
}

static void
machine_push (MachineState *state,
              int           v)
{
    state->stack = g_slist_prepend (state->stack, GINT_TO_POINTER (v));
}

static int
machine_pop (MachineState *state)
{
    int v;
    v = GPOINTER_TO_INT (state->stack->data);
    state->stack = g_slist_delete_link (state->stack, state->stack);
    return v;
}