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

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2012-01-27  Paolo Carlini  <paolo.carlini@oracle.com>

	PR libstdc++/51795
	* include/bits/random.h (linear_congruential_generator): Add
	static_assert preventing instantiation for values of 'a' and 'm'
	currently handled incorrectly but _Mod::__calc.
	* include/bits/random.tcc (seed_seq::generate): Avoid unsafe
	uses of _Mod::__calc.

From-SVN: r183655
This commit is contained in:
Paolo Carlini 2012-01-27 23:30:28 +00:00 committed by Paolo Carlini
parent af5c13eb04
commit d9c257a7e2
3 changed files with 22 additions and 6 deletions
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9
libstdc++-v3/ChangeLog
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@ -1,3 +1,12 @@
2012-01-27 Paolo Carlini <paolo.carlini@oracle.com>
PR libstdc++/51795
* include/bits/random.h (linear_congruential_generator): Add
static_assert preventing instantiation for values of 'a' and 'm'
currently handled incorrectly but _Mod::__calc.
* include/bits/random.tcc (seed_seq::generate): Avoid unsafe
uses of _Mod::__calc.
2012-01-27 Jakub Jelinek <jakub@redhat.com>
PR libstdc++/51798

7
libstdc++-v3/include/bits/random.h
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@ -1,6 +1,6 @@
// random number generation -*- C++ -*-
// Copyright (C) 2009, 2010, 2011 Free Software Foundation, Inc.
// Copyright (C) 2009, 2010, 2011, 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
@ -174,6 +174,11 @@ _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;

12
libstdc++-v3/include/bits/random.tcc
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@ -1,6 +1,6 @@
// random number generation (out of line) -*- C++ -*-
// Copyright (C) 2009, 2010, 2011 Free Software Foundation, Inc.
// Copyright (C) 2009, 2010, 2011, 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
@ -49,6 +49,8 @@ namespace std _GLIBCXX_VISIBILITY(default)
//
// 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
{
@ -2771,8 +2773,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
^ __begin[(__k + __p) % __n]
^ __begin[(__k - 1) % __n]);
_Type __r1 = __arg ^ (__arg >> 27);
__r1 = __detail::__mod<_Type, __detail::_Shift<_Type, 32>::__value,
1664525u, 0u>(__r1);
__r1 = __detail::__mod<_Type,
__detail::_Shift<_Type, 32>::__value>(1664525u * __r1);
_Type __r2 = __r1;
if (__k == 0)
__r2 += __s;
@ -2793,8 +2795,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
+ __begin[(__k + __p) % __n]
+ __begin[(__k - 1) % __n]);
_Type __r3 = __arg ^ (__arg >> 27);
__r3 = __detail::__mod<_Type, __detail::_Shift<_Type, 32>::__value,
1566083941u, 0u>(__r3);
__r3 = __detail::__mod<_Type,
__detail::_Shift<_Type, 32>::__value>(1566083941u * __r3);
_Type __r4 = __r3 - __k % __n;
__r4 = __detail::__mod<_Type,
__detail::_Shift<_Type, 32>::__value>(__r4);