indexofmipmap.cpp

uint32_t indexof_mipmap(int level)
{
    int mask = ~((level - 1) >> 31);
    uint32_t lvl0sz = texture->iw * texture->ih;
    int kept = 2 * (level - 1) & mask;
    uint32_t mul = (0x55555555 >> ((32 - kept) - 2)) & mask;
    return (lvl0sz * mul) >> (kept & mask);
}