-B<bits> bits in length and stores it in B<rnd>. If B<top> is true, the
-two most significant bits of the number will be set to 1, so that the
-product of two such random numbers will always have 2*B<bits> length.
-If B<bottom> is true, the number will be odd.
+B<bits> bits in length and stores it in B<rnd>. If B<top> is -1, the
+most significant bit of the random number can be zero. If B<top> is 0,
+it is set to 1, and if B<top> is 1, the two most significant bits of
+the number will be set to 1, so that the product of two such random
+numbers will always have 2*B<bits> length. If B<bottom> is true, the
+number will be odd.