How does s16 convert to u32 in convert-bit-depth

#1

I wonder how does a s16 value convert into a u32 value.
what if the source value is negative?

#2

Does it just become 0 if it is negative?

#3

can any body help? :<

#4

does not support…
the specification says only support s16 to u8 or u8 to s16