Sigmoid function in hardware and a reconfigurable data processor including same

A reconfigurable data processor, comprising:

• an array of configurable units;
• and
• a bus system connected to the array of configurable units which communicates data at a processor clock rate, wherein a configurable unit (PCU) in the array of configurable units (CGRA) includes a functional unit, the functional unit including:
• an input register to store a variable X;
• a first circuit, having an input connected to the input register and an output, to generate a value eX on its output;
• a second circuit, having an input connected to the input register and an output, to generate an output which is a value (tan h(X/2)+1)/2 on its output;
• a comparator, having an input connected to the input register and an output, to generate a line on its output based on a comparison between X and a constant;
• and
• a selector to select between the outputs of the first circuit and the second circuit, in response to the output of the comparator, and provide an output representing a value sigmoid(X).

A method for computing a sigmoid function in a functional unit for a data processor, comprising:

• storing a variable X in an input register;
• generating a value eX on an output of a first circuit;
• generating a value (tan h(X/2)+1)/2 on an output of a second circuit;
• generating a signal on an output of a comparator based on a comparison between X and a constant;
• selecting between the outputs of the first circuit and the second circuit, in response to the output of the comparator, and providing a result representing a value sigmoid(X).