#include "virt_stack.h"
#include <malloc.h>

virt_stack *vstack_create() {
    return malloc(sizeof (virt_stack));
}

void vstack_destruct(virt_stack *st) {
    free(st);
}

void vstack_init(virt_stack *st) {
    st->cur = RUNTIME_VSTACK_SIZE;
    st->buf[st->cur] = 0;
}

void vstack_push(virt_stack *st, size_t value) {
    if (st->cur == 0) {
        assert(0);
    }
    --st->cur;
    st->buf[st->cur] = value;
}

size_t vstack_pop(virt_stack *st) {
    if (st->cur == RUNTIME_VSTACK_SIZE) {
        assert(0);
    }
    size_t value = st->buf[st->cur];
    ++st->cur;
    return value;
}

void* vstack_top(virt_stack *st) {
    return  st->buf + st->cur;
}

size_t vstack_size(virt_stack *st) {
    return RUNTIME_VSTACK_SIZE - st->cur;
}

size_t vstack_kth_from_start(virt_stack *st, size_t k) {
    assert(vstack_size(st) > k);
    return st->buf[RUNTIME_VSTACK_SIZE - 1 - k];
}