func bucketQuantile()

in metrics/testutil/metrics.go [297:326]

• 23 lines of code
• 7 McCabe index (conditional complexity)

func bucketQuantile(q float64, buckets []bucket) float64 {
	if q < 0 {
		return math.Inf(-1)
	}
	if q > 1 {
		return math.Inf(+1)
	}

	if len(buckets) < 2 {
		return math.NaN()
	}

	rank := q * buckets[len(buckets)-1].count
	b := sort.Search(len(buckets)-1, func(i int) bool { return buckets[i].count >= rank })

	if b == 0 {
		return buckets[0].upperBound * (rank / buckets[0].count)
	}

	if b == len(buckets)-1 && math.IsInf(buckets[b].upperBound, 1) {
		return buckets[len(buckets)-2].upperBound
	}

	// linear approximation of b-th bucket
	brank := rank - buckets[b-1].count
	bSize := buckets[b].upperBound - buckets[b-1].upperBound
	bCount := buckets[b].count - buckets[b-1].count

	return buckets[b-1].upperBound + bSize*(brank/bCount)
}