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re PR libstdc++/51795 (linear_congruential_engine doesn't work correctly)

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2012-04-29  Marc Glisse  <marc.glisse@inria.fr>
	    Paolo Carlini  <paolo.carlini@oracle.com>

	PR libstdc++/51795
	* include/bits/stl_algobase.h (__lg<>(_Size)): Remove.
	(__lg(int), __lg(unsigned), __lg(long), __lg(unsigned long),
	__lg(long long), __lg(unsigned long long)): Define constexpr.
	* include/bits/random.h (_Mod<>): Overcome Schrage's algorithm
	limitations.
	(__mod): Adjust.
	(linear_congruential): Remove FIXME static_assert.
	* include/bits/random.tcc (_Mod<>): Adjust.
	* testsuite/26_numerics/random/linear_congruential_engine/operators/
	51795.cc: New.

Co-Authored-By: Paolo Carlini <paolo.carlini@oracle.com>

From-SVN: r186948
This commit is contained in:
Marc Glisse 2012-04-30 01:36:09 +02:00 • committed by Paolo Carlini
parent 143a1ce16c
commit cf48c25519
5 changed files with 165 additions and 73 deletions
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15
libstdc++-v3/ChangeLog
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@ -1,3 +1,18 @@
2012-04-29 Marc Glisse <marc.glisse@inria.fr>
Paolo Carlini <paolo.carlini@oracle.com>
PR libstdc++/51795
* include/bits/stl_algobase.h (__lg<>(_Size)): Remove.
(__lg(int), __lg(unsigned), __lg(long), __lg(unsigned long),
__lg(long long), __lg(unsigned long long)): Define constexpr.
* include/bits/random.h (_Mod<>): Overcome Schrage's algorithm
limitations.
(__mod): Adjust.
(linear_congruential): Remove FIXME static_assert.
* include/bits/random.tcc (_Mod<>): Adjust.
* testsuite/26_numerics/random/linear_congruential_engine/operators/
51795.cc: New.
2012-04-29 Jonathan Wakely <jwakely.gcc@gmail.com>
* include/std/functional (function::function(F)): LWG 2132: Disable

78
libstdc++-v3/include/bits/random.h
View file

@ -76,15 +76,78 @@ _GLIBCXX_END_NAMESPACE_VERSION
struct _Shift<_UIntType, __w, true>
{ static const _UIntType __value = _UIntType(1) << __w; };
template<typename _Tp, _Tp __m, _Tp __a, _Tp __c, bool>
struct _Mod;
template<int __s,
int __which = ((__s <= __CHAR_BIT__ * sizeof (int))
+ (__s <= __CHAR_BIT__ * sizeof (long))
+ (__s <= __CHAR_BIT__ * sizeof (long long))
/* assume long long no bigger than __int128 */
+ (__s <= 128))>
struct _Select_uint_least_t
{
static_assert(__which < 0, /* needs to be dependent */
"sorry, would be too much trouble for a slow result");
};
template<int __s>
struct _Select_uint_least_t<__s, 4>
{ typedef unsigned int type; };
template<int __s>
struct _Select_uint_least_t<__s, 3>
{ typedef unsigned long type; };
template<int __s>
struct _Select_uint_least_t<__s, 2>
{ typedef unsigned long long type; };
#ifdef _GLIBCXX_USE_INT128
template<int __s>
struct _Select_uint_least_t<__s, 1>
{ typedef unsigned __int128 type; };
#endif
// Assume a != 0, a < m, c < m, x < m.
template<typename _Tp, _Tp __m, _Tp __a, _Tp __c,
bool __big_enough = (!(__m & (__m - 1))
|| (_Tp(-1) - __c) / __a >= __m - 1),
bool __schrage_ok = __m % __a < __m / __a>
struct _Mod
{
typedef typename _Select_uint_least_t<std::__lg(__a)
+ std::__lg(__m) + 2>::type _Tp2;
static _Tp
__calc(_Tp __x)
{ return static_cast<_Tp>((_Tp2(__a) * __x + __c) % __m); }
};
// Schrage.
template<typename _Tp, _Tp __m, _Tp __a, _Tp __c>
struct _Mod<_Tp, __m, __a, __c, false, true>
{
static _Tp
__calc(_Tp __x);
};
// Special cases:
// - for m == 2^n or m == 0, unsigned integer overflow is safe.
// - a * (m - 1) + c fits in _Tp, there is no overflow.
template<typename _Tp, _Tp __m, _Tp __a, _Tp __c, bool __s>
struct _Mod<_Tp, __m, __a, __c, true, __s>
{
static _Tp
__calc(_Tp __x)
{
_Tp __res = __a * __x + __c;
if (__m)
__res %= __m;
return __res;
}
};
// Dispatch based on modulus value to prevent divide-by-zero compile-time
// errors when m == 0.
template<typename _Tp, _Tp __m, _Tp __a = 1, _Tp __c = 0>
inline _Tp
__mod(_Tp __x)
{ return _Mod<_Tp, __m, __a, __c, __m == 0>::__calc(__x); }
{ return _Mod<_Tp, __m, __a, __c>::__calc(__x); }
/*
* An adaptor class for converting the output of any Generator into
@ -174,11 +237,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
static_assert(__m == 0u || (__a < __m && __c < __m),
"template argument substituting __m out of bounds");
// XXX FIXME:
// _Mod::__calc should handle correctly __m % __a >= __m / __a too.
static_assert(__m % __a < __m / __a,
"sorry, not implemented yet: try a smaller 'a' constant");
public:
/** The type of the generated random value. */
typedef _UIntType result_type;

78
libstdc++-v3/include/bits/random.tcc
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@ -41,58 +41,42 @@ namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
// General case for x = (ax + c) mod m -- use Schrage's algorithm to
// avoid integer overflow.
//
// Because a and c are compile-time integral constants the compiler
// kindly elides any unreachable paths.
// General case for x = (ax + c) mod m -- use Schrage's algorithm
// to avoid integer overflow.
//
// Preconditions: a > 0, m > 0.
//
// XXX FIXME: as-is, only works correctly for __m % __a < __m / __a.
//
template<typename _Tp, _Tp __m, _Tp __a, _Tp __c, bool>
struct _Mod
{
static _Tp
__calc(_Tp __x)
{
if (__a == 1)
__x %= __m;
else
{
static const _Tp __q = __m / __a;
static const _Tp __r = __m % __a;
_Tp __t1 = __a * (__x % __q);
_Tp __t2 = __r * (__x / __q);
if (__t1 >= __t2)
__x = __t1 - __t2;
else
__x = __m - __t2 + __t1;
}
if (__c != 0)
{
const _Tp __d = __m - __x;
if (__d > __c)
__x += __c;
else
__x = __c - __d;
}
return __x;
}
};
// Special case for m == 0 -- use unsigned integer overflow as modulo
// operator.
// Note: only works correctly for __m % __a < __m / __a.
template<typename _Tp, _Tp __m, _Tp __a, _Tp __c>
struct _Mod<_Tp, __m, __a, __c, true>
_Tp
_Mod<_Tp, __m, __a, __c, false, true>::
__calc(_Tp __x)
{
static _Tp
__calc(_Tp __x)
{ return __a * __x + __c; }
};
if (__a == 1)
__x %= __m;
else
{
static const _Tp __q = __m / __a;
static const _Tp __r = __m % __a;
_Tp __t1 = __a * (__x % __q);
_Tp __t2 = __r * (__x / __q);
if (__t1 >= __t2)
__x = __t1 - __t2;
else
__x = __m - __t2 + __t1;
}
if (__c != 0)
{
const _Tp __d = __m - __x;
if (__d > __c)
__x += __c;
else
__x = __c - __d;
}
return __x;
}
template<typename _InputIterator, typename _OutputIterator,
typename _UnaryOperation>

22
libstdc++-v3/include/bits/stl_algobase.h
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@ -975,37 +975,27 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
/// This is a helper function for the sort routines and for random.tcc.
// Precondition: __n > 0.
template<typename _Size>
inline _Size
__lg(_Size __n)
{
_Size __k;
for (__k = 0; __n != 0; __n >>= 1)
++__k;
return __k - 1;
}
inline int
inline _GLIBCXX_CONSTEXPR int
__lg(int __n)
{ return sizeof(int) * __CHAR_BIT__ - 1 - __builtin_clz(__n); }
inline unsigned
inline _GLIBCXX_CONSTEXPR unsigned
__lg(unsigned __n)
{ return sizeof(int) * __CHAR_BIT__ - 1 - __builtin_clz(__n); }
inline long
inline _GLIBCXX_CONSTEXPR long
__lg(long __n)
{ return sizeof(long) * __CHAR_BIT__ - 1 - __builtin_clzl(__n); }
inline unsigned long
inline _GLIBCXX_CONSTEXPR unsigned long
__lg(unsigned long __n)
{ return sizeof(long) * __CHAR_BIT__ - 1 - __builtin_clzl(__n); }
inline long long
inline _GLIBCXX_CONSTEXPR long long
__lg(long long __n)
{ return sizeof(long long) * __CHAR_BIT__ - 1 - __builtin_clzll(__n); }
inline unsigned long long
inline _GLIBCXX_CONSTEXPR unsigned long long
__lg(unsigned long long __n)
{ return sizeof(long long) * __CHAR_BIT__ - 1 - __builtin_clzll(__n); }

45
libstdc++-v3/testsuite/26_numerics/random/linear_congruential_engine/operators/51795.cc Normal file
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@ -0,0 +1,45 @@
// { dg-options "-std=gnu++11" }
// { dg-require-cstdint "" }
//
// Copyright (C) 2012 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library. This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.
//
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License along
// with this library; see the file COPYING3. If not see
// <http://www.gnu.org/licenses/>.
// 26.5.3.1 class template linear_congruential_engine [rand.eng.lcong]
#include <random>
#include <testsuite_hooks.h>
void test01()
{
bool test __attribute__((unused)) = true;
typedef std::linear_congruential_engine<std::uint64_t, 1103515245ULL,
12345, 2147483648ULL> engine;
engine eng(1103527590ULL);
for (unsigned it = 0; it < 1000; ++it)
{
std::uint64_t num = eng();
VERIFY( (num >= eng.min() && num <= eng.max()) );
}
}
int main()
{
test01();
return 0;
}