-Sets all LSBs leading up to where an LSB in the src is set. If the second
-operand is non-zero, this process begins each time from where 1s are set in the
-second operand.
+Sets all LSBs leading up to (excluding) where an LSB in the src is set,
+and sets zeros including and following the src bit found.
+If the second operand is non-zero, this process continues the search
+(in the same LSB to MSB order) beginning each time (including the first time)
+from where 1s are set in the second operand.
+
+A side-effect of the search is that when src is zero, the output is all ones.
+If the second operand is non-zero and the src is zero, the output is a
+copy of the second operand.