A calculation processor for determining a digital output value from a digital input value based on an exponent value a, the processor comprising - a first calculation block that is configured to: a) determine a position number n denoting a position of a Most Significant Bit, MSB, of a significant part of the input value IN; b) set an intermediate value y = b a·n with b being a base value; c) set an error value err = IN / b n; and d) initialize a counter value k; - a second calculation block that is configured to perform repeatedly each of the following steps e),f), g1), g2), g3) until an exit criterion is fulfilled: e) increment the counter value k by 1; f) determine a power error value perr with perr = err b; g1) if the power error value perr is larger than or equal to an error threshold, adjust the intermediate value y by multiplying the intermediate value y with an adaptation value being dependent on the counter value k; g2) if the power error value perr is larger than or equal to the error threshold, set the error value err to the power error value perr divided by the base value b; g3) if the power error value perr is smaller than the error threshold, set the error value err to the power error value perr; and - a final calculation block that is configured to set the output value to the intermediate value y. - a first calculation block that is configured to: a) determine a position number n denoting a position of a Most Significant Bit, MSB, of a significant part of the input value IN; b) set an intermediate value y = b a·n with b being a base value; c) set an error value err = IN / b n; and d) initialize a counter value k; a) determine a position number n denoting a position of a Most Significant Bit, MSB, of a significant part of the input value IN; b) set an intermediate value y = b a·n with b being a base value; c) set an error value err = IN / b n; and d) initialize a counter value k; - a second calculation block that is configured to perform repeatedly each of the following steps e),f), g1), g2), g3) until an exit criterion is fulfilled: e) increment the counter value k by 1; f) determine a power error value perr with perr = err b; g1) if the power error value perr is larger than or equal to an error threshold, adjust the intermediate value y by multiplying the intermediate value y with an adaptation value being dependent on the counter value k; g2) if the power error value perr is larger than or equal to the error threshold, set the error value err to the power error value perr divided by the base value b; g3) if the power error value perr is smaller than the error threshold, set the error value err to the power error value perr; and e) increment the counter value k by 1; f) determine a power error value perr with perr = err b; g1) if the power error value perr is larger than or equal to an error threshold, adjust the intermediate value y by multiplying the intermediate value y with an adaptation value being dependent on the counter value k; g2) if the power error value perr is larger than or equal to the error threshold, set the error value err to the power error value perr divided by the base value b; g3) if the power error value perr is smaller than the error threshold, set the error value err to the power error value perr; - a final calculation block that is configured to set the output value to the intermediate value y.