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 <limits> 10 11 #include "base/basictypes.h" 12 #include "base/logging.h" 13 #include "base/strings/string_util.h" 14 15 namespace base { 16 17 int RandInt(int min, int max) { 18 DCHECK_LE(min, max); 19 20 uint64 range = static_cast<uint64>(max) - min + 1; 21 int result = min + static_cast<int>(base::RandGenerator(range)); 22 DCHECK_GE(result, min); 23 DCHECK_LE(result, max); 24 return result; 25 } 26 27 double RandDouble() { 28 return BitsToOpenEndedUnitInterval(base::RandUint64()); 29 } 30 31 double BitsToOpenEndedUnitInterval(uint64 bits) { 32 // We try to get maximum precision by masking out as many bits as will fit 33 // in the target type's mantissa, and raising it to an appropriate power to 34 // produce output in the range [0, 1). For IEEE 754 doubles, the mantissa 35 // is expected to accommodate 53 bits. 36 37 COMPILE_ASSERT(std::numeric_limits<double>::radix == 2, otherwise_use_scalbn); 38 static const int kBits = std::numeric_limits<double>::digits; 39 uint64 random_bits = bits & ((GG_UINT64_C(1) << kBits) - 1); 40 double result = ldexp(static_cast<double>(random_bits), -1 * kBits); 41 DCHECK_GE(result, 0.0); 42 DCHECK_LT(result, 1.0); 43 return result; 44 } 45 46 uint64 RandGenerator(uint64 range) { 47 DCHECK_GT(range, 0u); 48 // We must discard random results above this number, as they would 49 // make the random generator non-uniform (consider e.g. if 50 // MAX_UINT64 was 7 and |range| was 5, then a result of 1 would be twice 51 // as likely as a result of 3 or 4). 52 uint64 max_acceptable_value = 53 (std::numeric_limits<uint64>::max() / range) * range - 1; 54 55 uint64 value; 56 do { 57 value = base::RandUint64(); 58 } while (value > max_acceptable_value); 59 60 return value % range; 61 } 62 63 void RandBytes(void* output, size_t output_length) { 64 uint64 random_int; 65 size_t random_int_size = sizeof(random_int); 66 for (size_t i = 0; i < output_length; i += random_int_size) { 67 random_int = base::RandUint64(); 68 size_t copy_count = std::min(output_length - i, random_int_size); 69 memcpy(((uint8*)output) + i, &random_int, copy_count); 70 } 71 } 72 73 std::string RandBytesAsString(size_t length) { 74 DCHECK_GT(length, 0u); 75 std::string result; 76 RandBytes(WriteInto(&result, length + 1), length); 77 return result; 78 } 79 80 } // namespace base 81
