Repo created

TMessagesProj/jni/voip/webrtc/base/rand_util.cc

@@ -0,0 +1,82 @@
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "base/rand_util.h"
+
+#include <limits.h>
+#include <math.h>
+#include <stdint.h>
+
+#include <algorithm>
+#include <limits>
+
+#include "base/logging.h"
+#include "base/strings/string_util.h"
+
+namespace base {
+
+uint64_t RandUint64() {
+  uint64_t number;
+  RandBytes(&number, sizeof(number));
+  return number;
+}
+
+int RandInt(int min, int max) {
+  DCHECK_LE(min, max);
+
+  uint64_t range = static_cast<uint64_t>(max) - min + 1;
+  // |range| is at most UINT_MAX + 1, so the result of RandGenerator(range)
+  // is at most UINT_MAX.  Hence it's safe to cast it from uint64_t to int64_t.
+  int result =
+      static_cast<int>(min + static_cast<int64_t>(base::RandGenerator(range)));
+  DCHECK_GE(result, min);
+  DCHECK_LE(result, max);
+  return result;
+}
+
+double RandDouble() {
+  return BitsToOpenEndedUnitInterval(base::RandUint64());
+}
+
+double BitsToOpenEndedUnitInterval(uint64_t bits) {
+  // We try to get maximum precision by masking out as many bits as will fit
+  // in the target type's mantissa, and raising it to an appropriate power to
+  // produce output in the range [0, 1).  For IEEE 754 doubles, the mantissa
+  // is expected to accommodate 53 bits.
+
+  static_assert(std::numeric_limits<double>::radix == 2,
+                "otherwise use scalbn");
+  static const int kBits = std::numeric_limits<double>::digits;
+  uint64_t random_bits = bits & ((UINT64_C(1) << kBits) - 1);
+  double result = ldexp(static_cast<double>(random_bits), -1 * kBits);
+  DCHECK_GE(result, 0.0);
+  DCHECK_LT(result, 1.0);
+  return result;
+}
+
+uint64_t RandGenerator(uint64_t range) {
+  DCHECK_GT(range, 0u);
+  // We must discard random results above this number, as they would
+  // make the random generator non-uniform (consider e.g. if
+  // MAX_UINT64 was 7 and |range| was 5, then a result of 1 would be twice
+  // as likely as a result of 3 or 4).
+  uint64_t max_acceptable_value =
+      (std::numeric_limits<uint64_t>::max() / range) * range - 1;
+
+  uint64_t value;
+  do {
+    value = base::RandUint64();
+  } while (value > max_acceptable_value);
+
+  return value % range;
+}
+
+std::string RandBytesAsString(size_t length) {
+  DCHECK_GT(length, 0u);
+  std::string result;
+  RandBytes(WriteInto(&result, length + 1), length);
+  return result;
+}
+
+}  // namespace base