#### 23.1.12.25 Instruction powi

Synopsys:

Perform the exponentiation of the integer at the under top of the
stack. The exponent is the unsigned integer at the top of the
stack. If the exponent is 0, the result is 1.

Note that this instruction does NOT check for signed overflow, and
in case it occurs, the result contents are UB.

Stack: `( INT UINT -- INT UINT INT )`