Per the benchmarking spec:

For each micro-benchmark, the 10th, 25th, 50th, 75th, 90th, 95th, 98th and 99th percentiles will be recorded using the following algorithm:

• Given a 0-indexed array A of N iteration wall clock times
• Sort the array into ascending order (i.e. shortest time first)
• Let the index i for percentile p in the range [1,100] be defined as: i = int(N * p / 100) - 1