How do I get/set variables using bitmasks?

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C++

C

So I am trying to make a simple stack-based virtual machine, and i want the stack to be an array of type int8_t, so that every element is 1 byte. But I don't want to exclusively work with bytes, i want 16-, 32-, and 64-bit numbers to work too, therefore i need bitmasks.

This is currently the code:

#include <stdint.h>
#include <stdio.h>
#define STACKSIZE 65536

int8_t stack[STACKSIZE];
void push(int8_t);
int8_t pop();
void pushw(int16_t);
int16_t popw();
int64_t top = -1;

int main() {
	pushw(938);
	for (int i = 0; i < 10; i++)
	{
		printf("%d\n", stack[i]);
	}
	printf("\n\n%d", popw());
	return 0;
}

void push(int8_t x) {
	if (rsp == STACKSIZE - 1)
	{
		printf("Overflow!");
	}
	else
	{
		rsp++;
		stack[rsp] = x;
	}
}

int8_t pop() {
	if (rsp == -1) {
		printf("Underflow");
		return -1;
	}
	else {
		rsp--;
		return stack[rsp + 1];
	}
}

//LSB-MSB at push
//MSH-LSB at pop
void pushw(int16_t x) {
	push(x & 0x00FF);
	push(x & 0xFF00);
}

int16_t popw() {
	int16_t r = pop();
	r |= (pop() << 8);
	return r;
}

Expected output:

234 //I am not too good at decimal-binary conversion, but i think these are right
2
0
0
0
0
0
0
0
0


938

What i get instead:

-86
0
0
0
0
0
0
0
0
0

-22016

Please help.

What I have tried:

I have tried changing the order but then it gave me 0, -86 as the first two numbers and just returned -86 at the end with the popw();