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Add note and comment after assert for integer template type for factorial

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[SVN r67367]
This commit is contained in:
Paul A. Bristow
2010-12-20 16:02:33 +00:00
parent bae44eae90
commit 7523045cd0
1 changed files with 33 additions and 8 deletions
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41
doc/sf_and_dist/factorials.qbk
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@@ -27,18 +27,32 @@
[h4 Description]
[important
The functions described below are templates where the template argument T can not be deduced from the
The functions described below are templates where the template argument T CANNOT be deduced from the
arguments passed to the function. Therefore if you write something like:
`boost::math::factorial(2);`
You will get a compiler error, ususally indicating that there is no such function to be found. Instead you need to specifiy
the return type explicity and write:
You will get a (perhaps perplexing) compiler error, ususally indicating that there is no such function to be found.
Instead you need to specify the return type explicity and write:
`boost::math::factorial<double>(2);`
So that the return type is known. Further, the template argument must be a real-valued type such as `float` or `double`
and not an integer type - that would overflow far too easily!
So that the return type is known.
Furthermore, the template argument must be a real-valued type such as `float` or `double`
and not an integer type - that would overflow far too easily for quite small values of parameter `i`!
The source code `static_assert` and comment just after the will be:
``
BOOST_STATIC_ASSERT(!boost::is_integral<T>::value);
// factorial<unsigned int>(n) is not implemented
// because it would overflow integral type T for too small n
// to be useful. Use instead a floating-point type,
// and convert to an unsigned type if essential, for example:
// unsigned int nfac = static_cast<unsigned int>(factorial<double>(n));
// See factorial documentation for more detail.
``
]
template <class T>
@@ -128,13 +142,25 @@ arguments passed to the function. Therefore if you write something like:
`boost::math::double_factorial(2);`
You will get a compiler error, ususally indicating that there is no such function to be found. Instead you need to specifiy
You will get a (possibly perplexing) compiler error, ususally indicating that there is no such function to be found. Instead you need to specifiy
the return type explicity and write:
`boost::math::double_factorial<double>(2);`
So that the return type is known. Further, the template argument must be a real-valued type such as `float` or `double`
and not an integer type - that would overflow far too easily!
The source code `static_assert` and comment just after the will be:
``
BOOST_STATIC_ASSERT(!boost::is_integral<T>::value);
// factorial<unsigned int>(n) is not implemented
// because it would overflow integral type T for too small n
// to be useful. Use instead a floating-point type,
// and convert to an unsigned type if essential, for example:
// unsigned int nfac = static_cast<unsigned int>(factorial<double>(n));
// See factorial documentation for more detail.
``
]
[h4 Accuracy]
@@ -339,9 +365,8 @@ and
[endsect][/section:factorials Factorials]
[/
Copyright 2006 John Maddock and Paul A. Bristow.
Copyright 2006, 2010 John Maddock and Paul A. Bristow.
Distributed under the Boost Software License, Version 1.0.
(See accompanying file LICENSE_1_0.txt or copy at
http://www.boost.org/LICENSE_1_0.txt).
]