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


#define STACK_SIZE 2048

#define STACK_TYPE_INT 1

typedef struct {
	unsigned char stack[STACK_SIZE];
	unsigned char* head;
} VMS;

static void VMS_init(VMS* inst)
{
	memset(inst, 0, sizeof(VMS));
	inst->head = inst->stack + STACK_SIZE;
}

static inline size_t VMS_space(const VMS* inst)
{
	return inst->head - inst->stack;
}

static void VMS_assert(const VMS* inst, size_t space)
{
	assert(VMS_space(inst) >= space);
}

static inline int VMS_empty(const VMS* inst)
{
	return inst->head == (inst->stack + STACK_SIZE);
}

static void VMS_put(VMS* inst, unsigned char ch)
{
	VMS_assert(inst, 1)
	--(inst->head);
	*(inst->head) = ch;
}

static void VMS_put_int(VMS* inst, int num)
{
	VMS_assert(inst, sizeof(int));
	inst->head -= sizeof(int);
	*(int*)(inst->head) = num;
}
/**
 * Puts an int on the stack with a marked type
 */
static void VMS_putm_int(VMS* inst, int num)
{
	VMS_assert(inst, sizeof(int) + 1);
	inst->head -= sizeof(int);
	*(int*)(inst->head) = num;
	--(inst->head);
	*(inst->head) = STACK_TYPE_INT;
}

static void VMS_sum_int(VMS* inst)
{
	int sum = *(int*)(inst->head);
	inst->head += sizeof(int);
	*(int*)(inst->head) += sum;
}

static int VMS_head_int(const VMS* inst)
{
	return *(int*)(inst->head);
}

#define VMS_INSC_STOP 0
#define VMS_INSC_PUSH 1
#define VMS_INSC_SUM  2

static void VMS_run_instruc(VMS* inst, const unsigned char* instruc, size_t size)
{
	const unsigned char* instruc_end = instruc + size;
	while (instruc != instruc_end) {
		switch (*instruc) {
			case VMS_INSC_STOP:
			   return;
			case VMS_INSC_PUSH:
			   break;
			case VMS_INSC_SUM:
			   break;
			default:
			   fprintf("Got unknown instruction %u\n", *instruc);
			   exit(2);
		}
	}
}

int main(int argc, char const *argv[])
{
	puts("Stack Machine PoC");
	VMS a;
	VMS_init(&a);
	VMS_put_int(&a, 5);
	VMS_put_int(&a, 5);
	VMS_sum_int(&a);
	printf("result is %d\n", VMS_head_int(&a));
	return 0;
}