ARM Power/Exponential Function
The standard lib function for power on float data type is float powf(float, float). It appears to be well supported on my gcc-based STM32F4 setup. Given the performance of this MCU and its hardware FPU support for float, this function probably has excellent performance (it is likely using some taylor series or similar optimised numerical approximation). A look-up table approach might be faster if you can narrow your application to a specific set of power, but since such an implementation would be more complicated and less flexible, I would keep it as a possible optimisation if/when you determine that powf is too slow for your needs.