base/rand_util.cc

   1 // Copyright (c) 2008 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "base/rand_util.h"
   6
   7 #include <math.h>
   8
   9 #include <limits>
  10
  11 #include "base/basictypes.h"
  12 #include "base/logging.h"
  13
  14 namespace base {
  15
  16 int RandInt(int min, int max) {
  17   DCHECK(min <= max);
  18
  19   uint64 range = static_cast<int64>(max) - min + 1;
  20   uint64 number = base::RandUint64();
  21   int result = min + static_cast<int>(number % range);
  22   DCHECK(result >= min && result <= max);
  23   return result;
  24 }
  25
  26 double RandDouble() {
  27   // We try to get maximum precision by masking out as many bits as will fit
  28   // in the target type's mantissa, and raising it to an appropriate power to
  29   // produce output in the range [0, 1).  For IEEE 754 doubles, the mantissa
  30   // is expected to accommodate 53 bits.
  31
  32   COMPILE_ASSERT(std::numeric_limits<double>::radix == 2, otherwise_use_scalbn);
  33   static const int kBits = std::numeric_limits<double>::digits;
  34   uint64 random_bits = base::RandUint64() & ((GG_UINT64_C(1) << kBits) - 1);
  35   double result = ldexp(static_cast<double>(random_bits), -1 * kBits);
  36   DCHECK(result >= 0.0 && result < 1.0);
  37   return result;
  38 }
  39
  40 }  // namespace base