1 // Copyright (c) 2010 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<uint64>(max) - min + 1; 20 int result = min + static_cast<int>(base::RandGenerator(range)); 21 DCHECK(result >= min && result <= max); 22 return result; 23 } 24 25 double RandDouble() { 26 // We try to get maximum precision by masking out as many bits as will fit 27 // in the target type's mantissa, and raising it to an appropriate power to 28 // produce output in the range [0, 1). For IEEE 754 doubles, the mantissa 29 // is expected to accommodate 53 bits. 30 31 COMPILE_ASSERT(std::numeric_limits<double>::radix == 2, otherwise_use_scalbn); 32 static const int kBits = std::numeric_limits<double>::digits; 33 uint64 random_bits = base::RandUint64() & ((GG_UINT64_C(1) << kBits) - 1); 34 double result = ldexp(static_cast<double>(random_bits), -1 * kBits); 35 DCHECK(result >= 0.0 && result < 1.0); 36 return result; 37 } 38 39 uint64 RandGenerator(uint64 max) { 40 DCHECK_GT(max, 0ULL); 41 return base::RandUint64() % max; 42 } 43 44 } // namespace base 45
