expr "raise to power" operator, similar to pow function
Returns an integer value if both arguments are integers, and double-precision floating-point otherwise.
The left operand may be any integer from Tcl's unlimited integer range.
The right operand is limited to a max integer value of 268435455 (0xfffffff) (28 bits). (Unless the left operand is -1, 0, or 1, so that the answer is trivial).
Expect to wait a long while for [expr 2**0xfffffff] to return.