1 files changed, 227 insertions, 0 deletions
diff --git a/test/core/util/histogram.cc b/test/core/util/histogram.cc
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+++ b/test/core/util/histogram.cc
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+/*
+ *
+ * Copyright 2015 gRPC authors.
+ *
+ * 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.
+ *
+ */
+
+#include <math.h>
+#include <stddef.h>
+#include <string.h>
+
+#include <grpc/support/alloc.h>
+#include <grpc/support/log.h>
+#include <grpc/support/port_platform.h>
+#include <grpc/support/useful.h>
+
+#include "test/core/util/histogram.h"
+
+/* Histograms are stored with exponentially increasing bucket sizes.
+   The first bucket is [0, m) where m = 1 + resolution
+   Bucket n (n>=1) contains [m**n, m**(n+1))
+   There are sufficient buckets to reach max_bucket_start */
+
+struct grpc_histogram {
+  /* Sum of all values seen so far */
+  double sum;
+  /* Sum of squares of all values seen so far */
+  double sum_of_squares;
+  /* number of values seen so far */
+  double count;
+  /* m in the description */
+  double multiplier;
+  double one_on_log_multiplier;
+  /* minimum value seen */
+  double min_seen;
+  /* maximum value seen */
+  double max_seen;
+  /* maximum representable value */
+  double max_possible;
+  /* number of buckets */
+  size_t num_buckets;
+  /* the buckets themselves */
+  uint32_t* buckets;
+};
+
+/* determine a bucket index given a value - does no bounds checking */
+static size_t bucket_for_unchecked(grpc_histogram* h, double x) {
+  return (size_t)(log(x) * h->one_on_log_multiplier);
+}
+
+/* bounds checked version of the above */
+static size_t bucket_for(grpc_histogram* h, double x) {
+  size_t bucket = bucket_for_unchecked(h, GPR_CLAMP(x, 1.0, h->max_possible));
+  GPR_ASSERT(bucket < h->num_buckets);
+  return bucket;
+}
+
+/* at what value does a bucket start? */
+static double bucket_start(grpc_histogram* h, double x) {
+  return pow(h->multiplier, x);
+}
+
+grpc_histogram* grpc_histogram_create(double resolution,
+                                      double max_bucket_start) {
+  grpc_histogram* h = (grpc_histogram*)gpr_malloc(sizeof(grpc_histogram));
+  GPR_ASSERT(resolution > 0.0);
+  GPR_ASSERT(max_bucket_start > resolution);
+  h->sum = 0.0;
+  h->sum_of_squares = 0.0;
+  h->multiplier = 1.0 + resolution;
+  h->one_on_log_multiplier = 1.0 / log(1.0 + resolution);
+  h->max_possible = max_bucket_start;
+  h->count = 0.0;
+  h->min_seen = max_bucket_start;
+  h->max_seen = 0.0;
+  h->num_buckets = bucket_for_unchecked(h, max_bucket_start) + 1;
+  GPR_ASSERT(h->num_buckets > 1);
+  GPR_ASSERT(h->num_buckets < 100000000);
+  h->buckets = (uint32_t*)gpr_zalloc(sizeof(uint32_t) * h->num_buckets);
+  return h;
+}
+
+void grpc_histogram_destroy(grpc_histogram* h) {
+  gpr_free(h->buckets);
+  gpr_free(h);
+}
+
+void grpc_histogram_add(grpc_histogram* h, double x) {
+  h->sum += x;
+  h->sum_of_squares += x * x;
+  h->count++;
+  if (x < h->min_seen) {
+    h->min_seen = x;
+  }
+  if (x > h->max_seen) {
+    h->max_seen = x;
+  }
+  h->buckets[bucket_for(h, x)]++;
+}
+
+int grpc_histogram_merge(grpc_histogram* dst, const grpc_histogram* src) {
+  if ((dst->num_buckets != src->num_buckets) ||
+      (dst->multiplier != src->multiplier)) {
+    /* Fail because these histograms don't match */
+    return 0;
+  }
+  grpc_histogram_merge_contents(dst, src->buckets, src->num_buckets,
+                                src->min_seen, src->max_seen, src->sum,
+                                src->sum_of_squares, src->count);
+  return 1;
+}
+
+void grpc_histogram_merge_contents(grpc_histogram* dst, const uint32_t* data,
+                                   size_t data_count, double min_seen,
+                                   double max_seen, double sum,
+                                   double sum_of_squares, double count) {
+  size_t i;
+  GPR_ASSERT(dst->num_buckets == data_count);
+  dst->sum += sum;
+  dst->sum_of_squares += sum_of_squares;
+  dst->count += count;
+  if (min_seen < dst->min_seen) {
+    dst->min_seen = min_seen;
+  }
+  if (max_seen > dst->max_seen) {
+    dst->max_seen = max_seen;
+  }
+  for (i = 0; i < dst->num_buckets; i++) {
+    dst->buckets[i] += data[i];
+  }
+}
+
+static double threshold_for_count_below(grpc_histogram* h, double count_below) {
+  double count_so_far;
+  double lower_bound;
+  double upper_bound;
+  size_t lower_idx;
+  size_t upper_idx;
+
+  if (h->count == 0) {
+    return 0.0;
+  }
+
+  if (count_below <= 0) {
+    return h->min_seen;
+  }
+  if (count_below >= h->count) {
+    return h->max_seen;
+  }
+
+  /* find the lowest bucket that gets us above count_below */
+  count_so_far = 0.0;
+  for (lower_idx = 0; lower_idx < h->num_buckets; lower_idx++) {
+    count_so_far += h->buckets[lower_idx];
+    if (count_so_far >= count_below) {
+      break;
+    }
+  }
+  if (count_so_far == count_below) {
+    /* this bucket hits the threshold exactly... we should be midway through
+       any run of zero values following the bucket */
+    for (upper_idx = lower_idx + 1; upper_idx < h->num_buckets; upper_idx++) {
+      if (h->buckets[upper_idx]) {
+        break;
+      }
+    }
+    return (bucket_start(h, (double)lower_idx) +
+            bucket_start(h, (double)upper_idx)) /
+           2.0;
+  } else {
+    /* treat values as uniform throughout the bucket, and find where this value
+       should lie */
+    lower_bound = bucket_start(h, (double)lower_idx);
+    upper_bound = bucket_start(h, (double)(lower_idx + 1));
+    return GPR_CLAMP(upper_bound - (upper_bound - lower_bound) *
+                                       (count_so_far - count_below) /
+                                       h->buckets[lower_idx],
+                     h->min_seen, h->max_seen);
+  }
+}
+
+double grpc_histogram_percentile(grpc_histogram* h, double percentile) {
+  return threshold_for_count_below(h, h->count * percentile / 100.0);
+}
+
+double grpc_histogram_mean(grpc_histogram* h) {
+  GPR_ASSERT(h->count != 0);
+  return h->sum / h->count;
+}
+
+double grpc_histogram_stddev(grpc_histogram* h) {
+  return sqrt(grpc_histogram_variance(h));
+}
+
+double grpc_histogram_variance(grpc_histogram* h) {
+  if (h->count == 0) return 0.0;
+  return (h->sum_of_squares * h->count - h->sum * h->sum) /
+         (h->count * h->count);
+}
+
+double grpc_histogram_maximum(grpc_histogram* h) { return h->max_seen; }
+
+double grpc_histogram_minimum(grpc_histogram* h) { return h->min_seen; }
+
+double grpc_histogram_count(grpc_histogram* h) { return h->count; }
+
+double grpc_histogram_sum(grpc_histogram* h) { return h->sum; }
+
+double grpc_histogram_sum_of_squares(grpc_histogram* h) {
+  return h->sum_of_squares;
+}
+
+const uint32_t* grpc_histogram_get_contents(grpc_histogram* h, size_t* size) {
+  *size = h->num_buckets;
+  return h->buckets;
+}