They don't - trunc(result \* 255 + 0.5) is just round(result \* 255), i.e. error...

account42 63 days ago | parent | context | favorite | on: Should you normalize RGB values by 255 or 256?

They don't - trunc(result * 255 + 0.5) is just round(result * 255), i.e. error is on average 0 whereas trunc(result * 256) has an average bias of -0.5.