michael@0: // Copyright (c) 2008 The Chromium Authors. All rights reserved.
michael@0: // Use of this source code is governed by a BSD-style license that can be
michael@0: // found in the LICENSE file.
michael@0: 
michael@0: #include "base/rand_util.h"
michael@0: 
michael@0: #include <math.h>
michael@0: 
michael@0: #include <limits>
michael@0: 
michael@0: #include "base/basictypes.h"
michael@0: #include "base/logging.h"
michael@0: 
michael@0: namespace base {
michael@0: 
michael@0: int RandInt(int min, int max) {
michael@0:   DCHECK(min <= max);
michael@0: 
michael@0:   uint64_t range = static_cast<int64_t>(max) - min + 1;
michael@0:   uint64_t number = base::RandUint64();
michael@0:   int result = min + static_cast<int>(number % range);
michael@0:   DCHECK(result >= min && result <= max);
michael@0:   return result;
michael@0: }
michael@0: 
michael@0: double RandDouble() {
michael@0:   // We try to get maximum precision by masking out as many bits as will fit
michael@0:   // in the target type's mantissa, and raising it to an appropriate power to
michael@0:   // produce output in the range [0, 1).  For IEEE 754 doubles, the mantissa
michael@0:   // is expected to accommodate 53 bits.
michael@0: 
michael@0:   COMPILE_ASSERT(std::numeric_limits<double>::radix == 2, otherwise_use_scalbn);
michael@0:   static const int kBits = std::numeric_limits<double>::digits;
michael@0:   uint64_t random_bits = base::RandUint64() & ((GG_UINT64_C(1) << kBits) - 1);
michael@0:   double result = ldexp(static_cast<double>(random_bits), -1 * kBits);
michael@0:   DCHECK(result >= 0.0 && result < 1.0);
michael@0:   return result;
michael@0: }
michael@0: 
michael@0: }  // namespace base