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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
// Copyright (c) 2008 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(min <= max);
uint64_t range = static_cast<int64_t>(max) - min + 1;
uint64_t number = base::RandUint64();
int result = min + static_cast<int>(number % range);
DCHECK(result >= min && 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_t random_bits = base::RandUint64() & ((GG_UINT64_C(1) << kBits) - 1);
double result = ldexp(static_cast<double>(random_bits), -1 * kBits);
DCHECK(result >= 0.0 && result < 1.0);
return result;
}
} // namespace base
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