1 // Copyright (c) 2011 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 <algorithm> 10 #include <limits> 11 12 #include "base/basictypes.h" 13 #include "base/logging.h" 14 #include "base/strings/string_util.h" 15 16 namespace base { 17 18 int RandInt(int min, int max) { 19 DCHECK_LE(min, max); 20 21 uint64 range = static_cast<uint64>(max) - min + 1; 22 int result = min + static_cast<int>(base::RandGenerator(range)); 23 DCHECK_GE(result, min); 24 DCHECK_LE(result, max); 25 return result; 26 } 27 28 double RandDouble() { 29 return BitsToOpenEndedUnitInterval(base::RandUint64()); 30 } 31 32 double BitsToOpenEndedUnitInterval(uint64 bits) { 33 // We try to get maximum precision by masking out as many bits as will fit 34 // in the target type's mantissa, and raising it to an appropriate power to 35 // produce output in the range [0, 1). For IEEE 754 doubles, the mantissa 36 // is expected to accommodate 53 bits. 37 38 COMPILE_ASSERT(std::numeric_limits<double>::radix == 2, otherwise_use_scalbn); 39 static const int kBits = std::numeric_limits<double>::digits; 40 uint64 random_bits = bits & ((GG_UINT64_C(1) << kBits) - 1); 41 double result = ldexp(static_cast<double>(random_bits), -1 * kBits); 42 DCHECK_GE(result, 0.0); 43 DCHECK_LT(result, 1.0); 44 return result; 45 } 46 47 uint64 RandGenerator(uint64 range) { 48 DCHECK_GT(range, 0u); 49 // We must discard random results above this number, as they would 50 // make the random generator non-uniform (consider e.g. if 51 // MAX_UINT64 was 7 and |range| was 5, then a result of 1 would be twice 52 // as likely as a result of 3 or 4). 53 uint64 max_acceptable_value = 54 (std::numeric_limits<uint64>::max() / range) * range - 1; 55 56 uint64 value; 57 do { 58 value = base::RandUint64(); 59 } while (value > max_acceptable_value); 60 61 return value % range; 62 } 63 64 std::string RandBytesAsString(size_t length) { 65 DCHECK_GT(length, 0u); 66 std::string result; 67 RandBytes(WriteInto(&result, length + 1), length); 68 return result; 69 } 70 71 } // namespace base 72
