Stats.kt
/*
* Copyright (C) 2018 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package androidx.benchmark
import java.util.ArrayList
import kotlin.Double.Companion.NaN
import kotlin.math.pow
import kotlin.math.roundToLong
/**
* Provides statistics such as mean, median, min, max, and percentiles, given a list of input
* values.
*/
internal class Stats(data: List<Long>) {
val median: Long
val min: Long
val max: Long
val percentile90: Long
val percentile95: Long
val mean: Double = data.average()
val standardDeviation: Double
init {
val values = ArrayList(data).sorted()
val size = values.size
if (size < 1) {
throw IllegalArgumentException("At least one result is necessary.")
}
min = values.first()
max = values.last()
median = getPercentile(values, 50)
percentile90 = getPercentile(values, 90)
percentile95 = getPercentile(values, 95)
standardDeviation = if (size == 1) {
NaN
} else {
val sum = values.map { (it - mean).pow(2) }.sum()
Math.sqrt(sum / (size - 1).toDouble())
}
}
companion object {
internal fun lerp(a: Long, b: Long, ratio: Double): Long {
return (a * (1 - ratio) + b * (ratio)).roundToLong()
}
internal fun getPercentile(data: List<Long>, percentile: Int): Long {
val idealIndex = percentile.coerceIn(0, 100) / 100.0 * (data.size - 1)
val firstIndex = idealIndex.toInt()
val secondIndex = firstIndex + 1
val firstValue = data[firstIndex]
val secondValue = data.getOrElse(secondIndex) { firstValue }
return lerp(firstValue, secondValue, idealIndex - firstIndex)
}
}
}