func expHistToDistribution[N int64 | float64]()

in exporter/metric/metric.go [723:775]

• 43 lines of code
• 6 McCabe index (conditional complexity)

func expHistToDistribution[N int64 | float64](hist metricdata.ExponentialHistogramDataPoint[N], projectID string) *distribution.Distribution {
	// First calculate underflow bucket with all negatives + zeros.
	underflow := hist.ZeroCount
	negativeBuckets := hist.NegativeBucket.Counts
	for i := 0; i < len(negativeBuckets); i++ {
		underflow += negativeBuckets[i]
	}

	// Next, pull in remaining buckets.
	counts := make([]int64, len(hist.PositiveBucket.Counts)+2)
	bucketOptions := &distribution.Distribution_BucketOptions{}
	counts[0] = int64(underflow)
	positiveBuckets := hist.PositiveBucket.Counts
	for i := 0; i < len(positiveBuckets); i++ {
		counts[i+1] = int64(positiveBuckets[i])
	}
	// Overflow bucket is always empty
	counts[len(counts)-1] = 0

	if len(hist.PositiveBucket.Counts) == 0 {
		// We cannot send exponential distributions with no positive buckets,
		// instead we send a simple overflow/underflow histogram.
		bucketOptions.Options = &distribution.Distribution_BucketOptions_ExplicitBuckets{
			ExplicitBuckets: &distribution.Distribution_BucketOptions_Explicit{
				Bounds: []float64{0},
			},
		}
	} else {
		// Exponential histogram
		growth := math.Exp2(math.Exp2(-float64(hist.Scale)))
		scale := math.Pow(growth, float64(hist.PositiveBucket.Offset))
		bucketOptions.Options = &distribution.Distribution_BucketOptions_ExponentialBuckets{
			ExponentialBuckets: &distribution.Distribution_BucketOptions_Exponential{
				GrowthFactor:     growth,
				Scale:            scale,
				NumFiniteBuckets: int32(len(counts) - 2),
			},
		}
	}

	var mean float64
	if !math.IsNaN(float64(hist.Sum)) && hist.Count > 0 { // Avoid divide-by-zero
		mean = float64(hist.Sum) / float64(hist.Count)
	}

	return &distribution.Distribution{
		Count:         int64(hist.Count),
		Mean:          mean,
		BucketCounts:  counts,
		BucketOptions: bucketOptions,
		Exemplars:     toDistributionExemplar[N](hist.Exemplars, projectID),
	}
}