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 RandInt(int min,int max)16int 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 RandDouble()26double 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 41