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// Copyright (c) 2011 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "base/rand_util.h"
#include <math.h>
#include <limits>
#include "base/basictypes.h"
#include "base/logging.h"
namespace base {
int RandInt(int min, int max) {
DCHECK_LE(min, max);
uint64 range = static_cast<uint64>(max) - min + 1;
int result = min + static_cast<int>(base::RandGenerator(range));
DCHECK_GE(result, min);
DCHECK_LE(result, max);
return result;
}
double RandDouble() {
// We try to get maximum precision by masking out as many bits as will fit
// in the target type's mantissa, and raising it to an appropriate power to
// produce output in the range [0, 1). For IEEE 754 doubles, the mantissa
// is expected to accommodate 53 bits.
COMPILE_ASSERT(std::numeric_limits<double>::radix == 2, otherwise_use_scalbn);
static const int kBits = std::numeric_limits<double>::digits;
uint64 random_bits = base::RandUint64() & ((GG_UINT64_C(1) << kBits) - 1);
double result = ldexp(static_cast<double>(random_bits), -1 * kBits);
DCHECK_GE(result, 0.0);
DCHECK_LT(result, 1.0);
return result;
}
uint64 RandGenerator(uint64 max) {
DCHECK_GT(max, 0ULL);
return base::RandUint64() % max;
}
std::string RandBytesAsString(size_t length) {
const size_t kBitsPerChar = 8;
const int kCharsPerInt64 = sizeof(uint64)/sizeof(char);
std::string result(length, '\0');
uint64 entropy = 0;
for (size_t i = 0; i < result.size(); ++i) {
if (i % kCharsPerInt64 == 0)
entropy = RandUint64();
result[i] = static_cast<char>(entropy);
entropy >>= kBitsPerChar;
}
return result;
}
} // namespace base
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