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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 <stdint.h>
#include <algorithm>
#include <limits>
#include "base/logging.h"
#include "base/strings/string_util.h"
namespace base {
int RandInt(int min, int max) {
DCHECK_LE(min, max);
uint64_t range = static_cast<uint64_t>(max) - min + 1;
// |range| is at most UINT_MAX + 1, so the result of RandGenerator(range)
// is at most UINT_MAX. Hence it's safe to cast it from uint64_t to int64_t.
int result =
static_cast<int>(min + static_cast<int64_t>(base::RandGenerator(range)));
DCHECK_GE(result, min);
DCHECK_LE(result, max);
return result;
}
double RandDouble() {
return BitsToOpenEndedUnitInterval(base::RandUint64());
}
double BitsToOpenEndedUnitInterval(uint64_t bits) {
// 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.
static_assert(std::numeric_limits<double>::radix == 2,
"otherwise use scalbn");
static const int kBits = std::numeric_limits<double>::digits;
uint64_t random_bits = bits & ((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_t RandGenerator(uint64_t range) {
DCHECK_GT(range, 0u);
// We must discard random results above this number, as they would
// make the random generator non-uniform (consider e.g. if
// MAX_UINT64 was 7 and |range| was 5, then a result of 1 would be twice
// as likely as a result of 3 or 4).
uint64_t max_acceptable_value =
(std::numeric_limits<uint64_t>::max() / range) * range - 1;
uint64_t value;
do {
value = base::RandUint64();
} while (value > max_acceptable_value);
return value % range;
}
std::string RandBytesAsString(size_t length) {
DCHECK_GT(length, 0u);
std::string result;
RandBytes(WriteInto(&result, length + 1), length);
return result;
}
} // namespace base
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