kezhenxu94 commented on code in PR #10449:
URL: https://github.com/apache/skywalking/pull/10449#discussion_r1118374760


##########
oap-server/server-receiver-plugin/otel-receiver-plugin/src/main/java/org/apache/skywalking/oap/server/receiver/otel/otlp/OpenTelemetryMetricRequestProcessor.java:
##########
@@ -161,6 +163,54 @@ private static Map<Double, Long> buildBuckets(
         return result;
     }
 
+    /**
+     * ExponentialHistogram data points are an alternate representation to the 
Histogram data point in OpenTelemetry
+     * metric 
format(https://opentelemetry.io/docs/reference/specification/metrics/data-model/#exponentialhistogram).
+     * It uses scale, offset and bucket index to calculate the bound. Firstly, 
calculate the base using scale by
+     * formula: base = 2**(2**(-scale)). Then the upperBound of specific 
bucket can be calculated by formula:
+     * base**(offset+index+1). Above calculation way is about positive 
buckets. For the negative case, we just
+     * map them by their absolute value into the negative range using the same 
scale as the positive range. So the
+     * upperBound should be calculated as -base**(offset+index).
+     *
+     * @param positiveOffset       corresponding to positive Buckets' offset 
in ExponentialHistogramDataPoint
+     * @param positiveBucketCounts corresponding to positive Buckets' 
bucket_counts in ExponentialHistogramDataPoint
+     * @param negativeOffset       corresponding to negative Buckets' offset 
in ExponentialHistogramDataPoint
+     * @param negativeBucketCounts corresponding to negative Buckets' 
bucket_counts in ExponentialHistogramDataPoint
+     * @param scale                corresponding to scale in 
ExponentialHistogramDataPoint
+     * @return The map is a bucket set for histogram, the key is specific 
bucket's upperBound, the value is item count
+     * in this bucket lower than or equals to key(upperBound)
+     */
+    private static Map<Double, Long> buildBucketsFromExponentialHistogram(
+        int positiveOffset, final List<Long> positiveBucketCounts,
+        int negativeOffset, final List<Long> negativeBucketCounts, int scale) {
+
+        final Map<Double, Long> result = new HashMap<>();

Review Comment:
   > We could leave some comments here as a TBD about ignoring this, maybe one 
day, we will know how should we process this. WDYT?
   
   Good to me



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