Execution unit for evaluating functions using Newton Raphson iterations

A method of operating an execution unit to determine a function result of one or more input values, the execution unit comprising a plurality of processing circuits including at least one multiplier circuit, the method comprising:

• providing, by control circuitry, an initial estimate of a result of an operation to the at least one multiplier circuit of the plurality of processing circuits so as to perform processing, by the plurality of processing circuits, of the initial estimate to generate the function result, the processing comprising:
• applying a Newton Raphson iteration to the initial estimate to determine a preliminary function result;
• applying a reversal of the function to the preliminary function result to determine an error in the preliminary function result, including performing a subtraction between a first one of the input values and an approximation of the first one of the input values generated from the preliminary function result;
• and
• rounding the preliminary function result in dependence upon the error, including applying a unit in the last place (ULP) circuit to determine a ULP.

A method of operating an execution unit in a processor, the execution unit comprising a processing pipeline comprising a plurality of processing circuits comprising a plurality of multiplier circuits, wherein the processing pipeline is operable to evaluate a plurality of different functions, the method comprising:

• receiving an op code from a computer readable instruction, wherein the op code defines that the instruction evaluates a first function of the plurality of different functions to produce a function result;
• and
• in dependence upon the op code of the instruction, controlling multiplexers of the processing pipeline so as to control to which of the multiplier circuits of the processing pipeline, values from a preceding processing stage of the processing pipeline are directed so as to evaluate the first function,
• wherein evaluating the first function comprises providing an initial estimate of a result of an operation to the multiplier circuits so as perform processing, by the plurality of processing units, of the initial estimate to generate the function result, the processing comprising applying a Newton Raphson iteration to the initial estimate.