Do these computations with signed integers.
Do these computations with signed integers.

This is because NumPy contains a booby trap where if you multiply an
unsigned integer with a plain Python 'int', you will get back a float:
https://github.com/numpy/numpy/issues/5745

HIPERFIT/futhark,diku-dk/futhark,diku-dk/futhark,diku-dk/futhark,HIPERFIT/futhark,diku-dk/futhark,diku-dk/futhark,HIPERFIT/futhark