Activation accelerator for neural network accelerator

A method of applying a non-linear activation function to an input value using an activation accelerator, the method comprising:

• generating, at the activation accelerator, a converted value from an input value;
• receiving, at the activation accelerator, information identifying (i) a first subset of bits of the converted value and (ii) a second subset of bits of the converted value, and in dependence on the received information:
• generating, at the activation accelerator, an index from the first subset of bits of the converted value and an interpolation value from the second subset of bits of the converted value, wherein a number of bits of the index and a number of bits of the interpolation value is determined by the received information;
• retrieving multiple values from a look-up table based on the index, the look-up table configured to store a plurality of values representing the non-linear activation function;
• and
• generating, at the activation accelerator, an estimated result of the non-linear activation function for the input value by interpolating between the multiple values from the look-up table based on the interpolation value.

A non-transitory computer readable storage medium having stored thereon a computer readable dataset description of an activation accelerator for use in a neural network accelerator that, when processed in an integrated circuit manufacturing system, causes the integrated circuit manufacturing system to manufacture an integrated circuit embodying an activation accelerator comprising:

• a look-up table configured to store a plurality of values representing a non-linear activation function;
• and
• one or more activation pipelines, each activation pipeline comprising:
• a range conversion unit configured to receive an input value and generate a converted value from the input value;
• an index generation unit configured to receive information identifying (i) a first subset of bits of the converted value and (ii) a second subset of bits of the converted value, and in dependence on the received information:
• generate an index from the first subset of bits of the converted value, and
• generate an interpolation value from the second subset of bits of the converted value, wherein a number of bits of the index and a number of bits of the interpolation value is determined by the received information;
• a look-up table interface unit configured to retrieve multiple values from the look-up table based on the index;
• and
• an interpolation unit configured to generate an estimated result of the non-linear activation function for the input value by interpolating between the multiple values retrieved from the look-up table based on the interpolation value.