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/*
* Copyright 2009, Google Inc.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following disclaimer
* in the documentation and/or other materials provided with the
* distribution.
* * Neither the name of Google Inc. nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include <cstddef>
#include <iostream>
#include "rand.h"
#include "puritan_assert.h"
namespace Salem
{
namespace Puritan
{
static const unsigned a = 1103515245 ;
static const unsigned b = 12345;
// Convention:
// If seed passed in is zero, this class will use the strong random number
// generator from crypto API via CryptGenRandom()
// Otherwise fallback to the linear-congruential generator.
Rand::Rand (unsigned seed) : y (seed+1231)
{
crypt_provider_ = NULL;
available_ = 0;
if (seed == 0)
InitializeProvider();
}
unsigned Rand::rnd_uint(void)
{
unsigned result = 0;
// If there is no provider, use the LCG.
if (crypt_provider_ == NULL) {
y = (a * y + b);
result = y >> 4;
}
#ifdef _WIN32
// The following code is used for improved random-number generation.
// TODO: Investigate use of openssl, which may do this on all
// platforms, but will still require platform-specific seeding.
else {
// Maintain a cache of random values by getting a large batch
// on each call, since calling CryptGenRandom() is expensive.
// Note: This code is not thread-safe, neither is the original LCG.
// Use InterlockedDecrement/CompareXchg etc. if that has to change.
long chosen_index = --available_;
if (chosen_index < 0) {
// We are out of values, time to replenish the cache.
::CryptGenRandom(crypt_provider_, sizeof(cached_numbers_),
reinterpret_cast<BYTE*>(cached_numbers_));
available_ = kCacheSize;
chosen_index = --available_;
}
result = cached_numbers_[chosen_index];
}
#endif
return result;
}
double Rand::rnd_flt()
{
unsigned r = rnd_uint();
// We don't ask for the full range of random numbers because
// I see different rounding behavior on different machines at the limit.
unsigned mask = 0xffffff;
unsigned div = mask + 1;
double dr = r & mask;
double res = dr / div;
return res;
}
int Rand::range (int from, int to)
{
PURITAN_ASSERT (from <= to, "Range is malformed");
if (from == to)
{
return from;
}
double x = (rnd_flt ()) * (to - from) + from;
int r = static_cast <int>(x);
return r;
}
unsigned Rand::urange (unsigned from, unsigned to)
{
return range (from, to);
}
size_t Rand::srange (size_t from, size_t to)
{
return range (static_cast <int>(from),
static_cast <int>(to));
}
// Return random string from list of strings.
const char *Rand::from_list (const char **list)
{
unsigned int i;
for (i = 0; list[i]; i++)
;
unsigned rn = range (0, i);
return list[rn];
}
bool Rand::InitializeProvider() {
#ifdef _WIN32
int result = ::CryptAcquireContext(& crypt_provider_, NULL, NULL,
PROV_RSA_FULL,
CRYPT_VERIFYCONTEXT);
return (result != 0);
#else
// If there is no cryptographic PRNG, this is a noop.
return true;
#endif
}
}
}
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