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1 // Copyright (c) 2011 The Chromium Authors. All rights reserved. | 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 | 2 // Use of this source code is governed by a BSD-style license that can be |
3 // found in the LICENSE file. | 3 // found in the LICENSE file. |
4 | 4 |
5 #include "base/rand_util.h" | 5 #include "base/rand_util.h" |
6 | 6 |
7 #include <math.h> | 7 #include <math.h> |
8 | 8 |
9 #include <limits> | 9 #include <limits> |
10 | 10 |
(...skipping 27 matching lines...) Expand all Loading... | |
38 static const int kBits = std::numeric_limits<double>::digits; | 38 static const int kBits = std::numeric_limits<double>::digits; |
39 uint64 random_bits = bits & ((GG_UINT64_C(1) << kBits) - 1); | 39 uint64 random_bits = bits & ((GG_UINT64_C(1) << kBits) - 1); |
40 double result = ldexp(static_cast<double>(random_bits), -1 * kBits); | 40 double result = ldexp(static_cast<double>(random_bits), -1 * kBits); |
41 DCHECK_GE(result, 0.0); | 41 DCHECK_GE(result, 0.0); |
42 DCHECK_LT(result, 1.0); | 42 DCHECK_LT(result, 1.0); |
43 return result; | 43 return result; |
44 } | 44 } |
45 | 45 |
46 uint64 RandGenerator(uint64 max) { | 46 uint64 RandGenerator(uint64 max) { |
47 DCHECK_GT(max, 0ULL); | 47 DCHECK_GT(max, 0ULL); |
48 return base::RandUint64() % max; | 48 |
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 4 and max was 3, then a result of 1 would be twice | |
52 // as likely as a result of 0 or 2). | |
53 uint64 max_acceptable_value = | |
54 (std::numeric_limits<uint64>::max() / max) * max; | |
55 | |
56 uint64 value; | |
57 do { | |
58 value = base::RandUint64(); | |
59 } while (value > max_acceptable_value); | |
jar (doing other things)
2011/05/27 20:25:14
Very cute.... but I think there is a typo, and thi
Jói
2011/05/27 23:18:01
You're right, thanks for catching that. Fixed and
jar (doing other things)
2011/05/28 17:26:40
OK... With that change I'm convinced it is "right,
| |
60 | |
61 return value % max; | |
49 } | 62 } |
50 | 63 |
51 void RandBytes(void* output, size_t output_length) { | 64 void RandBytes(void* output, size_t output_length) { |
52 uint64 random_int; | 65 uint64 random_int; |
53 size_t random_int_size = sizeof(random_int); | 66 size_t random_int_size = sizeof(random_int); |
54 for (size_t i = 0; i < output_length; i += random_int_size) { | 67 for (size_t i = 0; i < output_length; i += random_int_size) { |
55 random_int = base::RandUint64(); | 68 random_int = base::RandUint64(); |
56 size_t copy_count = std::min(output_length - i, random_int_size); | 69 size_t copy_count = std::min(output_length - i, random_int_size); |
57 memcpy(((uint8*)output) + i, &random_int, copy_count); | 70 memcpy(((uint8*)output) + i, &random_int, copy_count); |
58 } | 71 } |
59 } | 72 } |
60 | 73 |
61 std::string RandBytesAsString(size_t length) { | 74 std::string RandBytesAsString(size_t length) { |
62 std::string result; | 75 std::string result; |
63 RandBytes(WriteInto(&result, length + 1), length); | 76 RandBytes(WriteInto(&result, length + 1), length); |
64 return result; | 77 return result; |
65 } | 78 } |
66 | 79 |
67 } // namespace base | 80 } // namespace base |
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