Formula to convert any dpi to any dpi

I need the formulas to calculate any dpi to any dpi. For example: mdpi to hdpi, xdpi to xxhdpi, etc. This website exactly does what I require but I am not able to find the logic for it. Any suggestions on what will be the formula for it?

All the logic is client-side, so simple inspection will show You the whole algoritm:

I've extracted it and simplified a little bit:

if (e == ldpi) {
    mdpi.value = (Number(ldpi.value) / 3) + Number(ldpi.value);
    hdpi.value =  Number(ldpi.value) * 2;
    xhdpi.value =  Number(mdpi.value) * 2;
    xxhdpi.value =  Number(mdpi.value) * 3;
    xxxhdpi.value =  Number(mdpi.value) * 4;
}
else if (e == mdpi) {
    ldpi.value =  (Number(mdpi.value) / 2) + (Number(mdpi.value) / 4);
    hdpi.value =  Number(ldpi.value) * 2;
    xhdpi.value =  Number(mdpi.value) * 2;
    xxhdpi.value =  Number(mdpi.value) * 3;
    xxxhdpi.value =  Number(mdpi.value) * 4;
}
else if (e == hdpi) {
    ldpi.value =  Number(hdpi.value) / 2;
    mdpi.value = (Number(ldpi.value) / 3) + Number(ldpi.value);
    xhdpi.value =  Number(mdpi.value) * 2;
    xxhdpi.value =  Number(mdpi.value) * 3;
    xxxhdpi.value =  Number(mdpi.value) * 4;
}
else if (e == xhdpi) {
    ldpi.value =  Number(e.value) - (Number(e.value) / 2 + Number(e.value) / 8);
    mdpi.value =  Number(e.value) / 2;
    hdpi.value =  Number(ldpi.value) * 2;
    xxhdpi.value =  Number(mdpi.value) * 3;
    xxxhdpi.value =  Number(mdpi.value) * 4;
}
else if (e == xxhdpi) {
    ldpi.value =  Number(e.value) / 4;
    mdpi.value = (Number(ldpi.value) / 3) + Number(ldpi.value);
    hdpi.value =  Number(ldpi.value) * 2;
    xhdpi.value = Number(mdpi.value * 2);
    xxxhdpi.value =  Number(mdpi.value) * 4;
}
else if (e == xxxhdpi) {
    const val = e.value / 4;
    ldpi.value =  val - (val / 4);
    mdpi.value = (Number(ldpi.value) / 3) + Number(ldpi.value);
    hdpi.value =  Number(ldpi.value) * 2;
    xhdpi.value = Number(mdpi.value * 2);
    xxhdpi.value =  Number(mdpi.value) * 3;
}

I think that the above code is pretty self explanatory, but the value e represents some dpi value. Then You should check if that value was ldpi, mdpi or any other and based on that You can calculate other densities.