1 // Copyright 2021 gRPC authors.
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License");
4 // you may not use this file except in compliance with the License.
5 // You may obtain a copy of the License at
6 //
7 //     http://www.apache.org/licenses/LICENSE-2.0
8 //
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS,
11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 // See the License for the specific language governing permissions and
13 // limitations under the License.
14 
15 #include <grpc/support/port_platform.h>
16 
17 #include "src/core/lib/debug/histogram_view.h"
18 
19 namespace grpc_core {
20 
Count() const21 double HistogramView::Count() const {
22   double sum = 0;
23   for (int i = 0; i < num_buckets; i++) {
24     sum += buckets[i];
25   }
26   return sum;
27 }
28 
ThresholdForCountBelow(double count_below) const29 double HistogramView::ThresholdForCountBelow(double count_below) const {
30   double lower_bound;
31   double upper_bound;
32   int upper_idx;
33 
34   // find the lowest bucket that gets us above count_below
35   double count_so_far = 0.0;
36   int lower_idx = 0;
37   for (; lower_idx < num_buckets; lower_idx++) {
38     count_so_far += static_cast<double>(buckets[lower_idx]);
39     if (count_so_far >= count_below) {
40       break;
41     }
42   }
43   if (count_so_far == count_below) {
44     // this bucket hits the threshold exactly... we should be midway through
45     // any run of zero values following the bucket
46     for (upper_idx = lower_idx + 1; upper_idx < num_buckets; upper_idx++) {
47       if (buckets[upper_idx]) {
48         break;
49       }
50     }
51     return (bucket_boundaries[lower_idx] + bucket_boundaries[upper_idx]) / 2.0;
52   } else {
53     // treat values as uniform throughout the bucket, and find where this value
54     // should lie
55     lower_bound = bucket_boundaries[lower_idx];
56     upper_bound = bucket_boundaries[lower_idx + 1];
57     return upper_bound - (upper_bound - lower_bound) *
58                              (count_so_far - count_below) /
59                              static_cast<double>(buckets[lower_idx]);
60   }
61 }
62 
Percentile(double p) const63 double HistogramView::Percentile(double p) const {
64   const double count = Count();
65   if (count == 0) return 0.0;
66   return ThresholdForCountBelow(count * p / 100.0);
67 }
68 
69 }  // namespace grpc_core
70