Approximate quantile estimation

Apparatus comprising:

• input circuitry arranged to receive a sequence of data values, wherein the data values span a range of values;
• a plurality of counters implemented in hardware, wherein each counter of the plurality of counters is configured to have a correspondence to a subrange within the range of values;
• data counter correspondence circuitry arranged to determine for each data value received by the input circuitry a corresponding counter of the plurality of counters and to apply an update to the corresponding counter of the plurality of counters;
• and
• approximate quantile determination circuitry arranged to generate at least one approximate quantile value for the sequence of data values received in dependence on respective counts of the plurality of counters,
• wherein the apparatus is configured to operate initially in a data population mode and subsequently in a quantile estimation mode, wherein the apparatus is configured to switch from the data population mode to the quantile estimation mode in response to count saturation of a threshold number of the plurality of counters.