1 files changed, 76 insertions, 0 deletions
diff --git a/src/include/histogram.h b/src/include/histogram.h
new file mode 100644
index 00000000000..c817b1ec175
--- /dev/null
+++ b/src/include/histogram.h
@@ -0,0 +1,76 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+/*
+ * Ceph - scalable distributed file system
+ *
+ * This is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License version 2.1, as published by the Free Software
+ * Foundation.  See file COPYING.
+ * Copyright 2013 Inktank
+ */
+
+#ifndef HISTOGRAM_H_
+#define HISTOGRAM_H_
+
+/**
+ * power of 2 histogram
+ */
+struct pow2_hist_t { //
+  /**
+   * histogram
+   *
+   * bin size is 2^index
+   * value is count of elements that are <= the current bin but > the previous bin.
+   */
+  vector<int32_t> h;
+
+private:
+  /// expand to at least another's size
+  void _expand_to(unsigned s) {
+    if (s > h.size())
+      h.resize(s, 0);
+  }
+  /// drop useless trailing 0's
+  void _contract() {
+    unsigned p = h.size();
+    while (p > 0 && h[p-1] == 0)
+      --p;
+    h.resize(p);
+  }
+
+public:
+  void clear() {
+    h.clear();
+  }
+  void set(int bin, int32_t v) {
+    _expand_to(bin + 1);
+    h[bin] = v;
+    _contract();
+  }
+
+  void add(const pow2_hist_t& o) {
+    _expand_to(o.h.size());
+    for (unsigned p = 0; p < o.h.size(); ++p)
+      h[p] += o.h[p];
+    _contract();
+  }
+  void sub(const pow2_hist_t& o) {
+    _expand_to(o.h.size());
+    for (unsigned p = 0; p < o.h.size(); ++p)
+      h[p] -= o.h[p];
+    _contract();
+  }
+
+  int32_t upper_bound() const {
+    return 1 << h.size();
+  }
+
+  void dump(Formatter *f) const;
+  void encode(bufferlist &bl) const;
+  void decode(bufferlist::iterator &bl);
+  static void generate_test_instances(std::list<pow2_hist_t*>& o);
+};
+WRITE_CLASS_ENCODER(pow2_hist_t)
+
+#endif /* HISTOGRAM_H_ */