<?php

function valida_variavel_zero_um($valor)
{
    if ($valor !== 0 && $valor !== 1)
    {
        return "inválido";
    }

    return $valor;
}

$tests = [0, 1, false, true, "0", "1", [], "", 0.0, -0.0, 1.0];

foreach ($tests as $test)
{
    var_dump( valida_variavel_zero_um($test) );
}