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< div class = "section" >
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< div class = "titlepage" > < div > < div > < h2 class = "title" style = "clear: both" >
< a name = "boost_integer.mask" > < / a > < a class = "link" href = "mask.html" title = "Integer Masks" > Integer Masks< / a >
< / h2 > < / div > < / div > < / div >
< div class = "toc" > < dl >
< dt > < span class = "section" > < a href = "mask.html#boost_integer.mask.overview" > Overview< / a > < / span > < / dt >
< dt > < span class = "section" > < a href = "mask.html#boost_integer.mask.synopsis" > Synopsis< / a > < / span > < / dt >
< dt > < span class = "section" > < a href = "mask.html#boost_integer.mask.single_bit_mask_class_template" > Single
Bit-Mask Class Template< / a > < / span > < / dt >
< dt > < span class = "section" > < a href = "mask.html#boost_integer.mask.group_bit_mask_class_template" > Group
Bit-Mask Class Template< / a > < / span > < / dt >
< dt > < span class = "section" > < a href = "mask.html#boost_integer.mask.implementation_notes" > Implementation
Notes< / a > < / span > < / dt >
< dt > < span class = "section" > < a href = "mask.html#boost_integer.mask.example" > Example< / a > < / span > < / dt >
< dt > < span class = "section" > < a href = "mask.html#boost_integer.mask.demonstration_program" > Demonstration
Program< / a > < / span > < / dt >
< dt > < span class = "section" > < a href = "mask.html#boost_integer.mask.rationale" > Rationale< / a > < / span > < / dt >
< dt > < span class = "section" > < a href = "mask.html#boost_integer.mask.credits" > Credits< / a > < / span > < / dt >
< / dl > < / div >
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< div class = "section" >
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< div class = "titlepage" > < div > < div > < h3 class = "title" >
< a name = "boost_integer.mask.overview" > < / a > < a class = "link" href = "mask.html#boost_integer.mask.overview" title = "Overview" > Overview< / a >
< / h3 > < / div > < / div > < / div >
< p >
The class templates in < a href = "../../../../../boost/integer/integer_mask.hpp" target = "_top" > < boost/integer/integer_mask.hpp> < / a >
provide bit masks for a certain bit position or a contiguous-bit pack of
a certain size. The types of the masking constants come from the < a class = "link" href = "integer.html" title = "Integer Type Selection" > integer
type selection templates< / a > header.
< / p >
< / div >
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< div class = "section" >
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< div class = "titlepage" > < div > < div > < h3 class = "title" >
< a name = "boost_integer.mask.synopsis" > < / a > < a class = "link" href = "mask.html#boost_integer.mask.synopsis" title = "Synopsis" > Synopsis< / a >
< / h3 > < / div > < / div > < / div >
< pre class = "programlisting" > < span class = "preprocessor" > #include< / span > < span class = "special" > < < / span > < span class = "identifier" > cstddef< / span > < span class = "special" > > < / span > < span class = "comment" > // for std::size_t
< / span >
< span class = "keyword" > namespace< / span > < span class = "identifier" > boost< / span >
< span class = "special" > {< / span >
< span class = "keyword" > template< / span > < span class = "special" > < < / span > < span class = "identifier" > std< / span > < span class = "special" > ::< / span > < span class = "identifier" > size_t< / span > < span class = "identifier" > Bit< / span > < span class = "special" > > < / span >
< span class = "keyword" > struct< / span > < span class = "identifier" > high_bit_mask_t< / span >
< span class = "special" > {< / span >
< span class = "keyword" > typedef< / span > < span class = "emphasis" > < em > implementation-defined-type< / em > < / span > < span class = "identifier" > least< / span > < span class = "special" > ;< / span >
< span class = "keyword" > typedef< / span > < span class = "emphasis" > < em > implementation-defined-type< / em > < / span > < span class = "identifier" > fast< / span > < span class = "special" > ;< / span >
< span class = "keyword" > static< / span > < span class = "keyword" > const< / span > < span class = "identifier" > least< / span > < span class = "identifier" > high_bit< / span > < span class = "special" > =< / span > < span class = "emphasis" > < em > implementation-defined< / em > < / span > < span class = "special" > ;< / span >
< span class = "keyword" > static< / span > < span class = "keyword" > const< / span > < span class = "identifier" > fast< / span > < span class = "identifier" > high_bit_fast< / span > < span class = "special" > =< / span > < span class = "emphasis" > < em > implementation-defined< / em > < / span > < span class = "special" > ;< / span >
< span class = "keyword" > static< / span > < span class = "keyword" > const< / span > < span class = "identifier" > std< / span > < span class = "special" > ::< / span > < span class = "identifier" > size_t< / span > < span class = "identifier" > bit_position< / span > < span class = "special" > =< / span > < span class = "identifier" > Bit< / span > < span class = "special" > ;< / span >
< span class = "special" > };< / span >
< span class = "keyword" > template< / span > < span class = "special" > < < / span > < span class = "identifier" > std< / span > < span class = "special" > ::< / span > < span class = "identifier" > size_t< / span > < span class = "identifier" > Bits< / span > < span class = "special" > > < / span >
< span class = "keyword" > struct< / span > < span class = "identifier" > low_bits_mask_t< / span >
< span class = "special" > {< / span >
< span class = "keyword" > typedef< / span > < span class = "emphasis" > < em > implementation-defined-type< / em > < / span > < span class = "identifier" > least< / span > < span class = "special" > ;< / span >
< span class = "keyword" > typedef< / span > < span class = "emphasis" > < em > implementation-defined-type< / em > < / span > < span class = "identifier" > fast< / span > < span class = "special" > ;< / span >
< span class = "keyword" > static< / span > < span class = "keyword" > const< / span > < span class = "identifier" > least< / span > < span class = "identifier" > sig_bits< / span > < span class = "special" > =< / span > < span class = "emphasis" > < em > implementation-defined< / em > < / span > < span class = "special" > ;< / span >
< span class = "keyword" > static< / span > < span class = "keyword" > const< / span > < span class = "identifier" > fast< / span > < span class = "identifier" > sig_bits_fast< / span > < span class = "special" > =< / span > < span class = "emphasis" > < em > implementation-defined< / em > < / span > < span class = "special" > ;< / span >
< span class = "keyword" > static< / span > < span class = "keyword" > const< / span > < span class = "identifier" > std< / span > < span class = "special" > ::< / span > < span class = "identifier" > size_t< / span > < span class = "identifier" > bit_count< / span > < span class = "special" > =< / span > < span class = "identifier" > Bits< / span > < span class = "special" > ;< / span >
< span class = "special" > };< / span >
< span class = "comment" > // Specializations for low_bits_mask_t exist for certain bit counts.
< / span >
< span class = "special" > }< / span > < span class = "comment" > // namespace boost
< / span > < / pre >
< / div >
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< div class = "section" >
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< div class = "titlepage" > < div > < div > < h3 class = "title" >
< a name = "boost_integer.mask.single_bit_mask_class_template" > < / a > < a class = "link" href = "mask.html#boost_integer.mask.single_bit_mask_class_template" title = "Single Bit-Mask Class Template" > Single
Bit-Mask Class Template< / a >
< / h3 > < / div > < / div > < / div >
< p >
The < code class = "literal" > boost::high_bit_mask_t< / code > class template provides constants
for bit masks representing the bit at a certain position. The masks are equivalent
to the value 2< sup > Bit< / sup > , where < code class = "literal" > Bit< / code > is the template parameter.
The bit position must be a nonnegative number from zero to < span class = "emphasis" > < em > Max< / em > < / span > ,
where Max is one less than the number of bits supported by the largest unsigned
built-in integral type. The following table describes the members of an instantiation
of < code class = "literal" > high_bit_mask_t< / code > .
< / p >
< div class = "table" >
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< a name = "boost_integer.mask.single_bit_mask_class_template.members_of_the__boost__high_bit_mask_t__class_template" > < / a > < p class = "title" > < b > Table  2.  Members of the `boost::high_bit_mask_t` Class Template< / b > < / p >
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< div class = "table-contents" > < table class = "table" summary = "Members of the `boost::high_bit_mask_t` Class Template" >
< colgroup >
< col >
< col >
< / colgroup >
< thead > < tr >
< th >
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< p >
Member
< / p >
< / th >
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< th >
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< p >
Meaning
< / p >
< / th >
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< / tr > < / thead >
< tbody >
< tr >
< td >
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< p >
< code class = "literal" > least< / code >
< / p >
< / td >
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< td >
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< p >
The smallest, unsigned, built-in type that supports the given bit
position.
< / p >
< / td >
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< / tr >
< tr >
< td >
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< p >
< code class = "literal" > fast< / code >
< / p >
< / td >
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< td >
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< p >
The easiest-to-manipulate analog of < code class = "literal" > least< / code > .
< / p >
< / td >
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< / tr >
< tr >
< td >
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< p >
< code class = "literal" > high_bit< / code >
< / p >
< / td >
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< td >
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< p >
A < code class = "literal" > least< / code > constant of the value 2< sup > Bit< / sup > .
< / p >
< / td >
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< / tr >
< tr >
< td >
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< p >
< code class = "literal" > high_bit_fast< / code >
< / p >
< / td >
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< td >
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< p >
A < code class = "literal" > fast< / code > analog of < code class = "literal" > high_bit< / code > .
< / p >
< / td >
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< / tr >
< tr >
< td >
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< p >
< code class = "literal" > bit_position< / code >
< / p >
< / td >
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< td >
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< p >
The value of the template parameter, in case its needed from a
renamed instantiation of the class template.
< / p >
< / td >
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< / tr >
< / tbody >
< / table > < / div >
< / div >
< br class = "table-break" >
< / div >
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< div class = "section" >
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< div class = "titlepage" > < div > < div > < h3 class = "title" >
< a name = "boost_integer.mask.group_bit_mask_class_template" > < / a > < a class = "link" href = "mask.html#boost_integer.mask.group_bit_mask_class_template" title = "Group Bit-Mask Class Template" > Group
Bit-Mask Class Template< / a >
< / h3 > < / div > < / div > < / div >
< p >
The < code class = "literal" > boost::low_bits_mask_t< / code > class template provides constants
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for bit masks equivalent to the value (2< sup > Bits< / sup > - 1), where < code class = "literal" > Bits< / code >
is the template parameter. The parameter < code class = "literal" > Bits< / code > must be
a non-negative integer from zero to < span class = "emphasis" > < em > Max< / em > < / span > , where Max is
the number of bits supported by the largest, unsigned, built-in integral
type. The following table describes the members of < code class = "literal" > low_bits_mask_t< / code > .
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< / p >
< div class = "table" >
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< a name = "boost_integer.mask.group_bit_mask_class_template.members_of_the___boost__low_bits_mask_t__class_template" > < / a > < p class = "title" > < b > Table  3.  Members of the [^boost::low_bits_mask_t] Class Template< / b > < / p >
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< div class = "table-contents" > < table class = "table" summary = "Members of the [^boost::low_bits_mask_t] Class Template" >
< colgroup >
< col >
< col >
< / colgroup >
< thead > < tr >
< th >
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< p >
Member
< / p >
< / th >
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< th >
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< p >
Meaning
< / p >
< / th >
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< / tr > < / thead >
< tbody >
< tr >
< td >
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< p >
< code class = "literal" > least< / code >
< / p >
< / td >
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< td >
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< p >
The smallest, unsigned built-in type that supports the given bit
count.
< / p >
< / td >
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< / tr >
< tr >
< td >
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< p >
< code class = "literal" > fast< / code >
< / p >
< / td >
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< td >
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< p >
The easiest-to-manipulate analog of < code class = "literal" > least< / code > .
< / p >
< / td >
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< / tr >
< tr >
< td >
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< p >
< code class = "literal" > sig_bits< / code >
< / p >
< / td >
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< td >
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< p >
A < code class = "literal" > least< / code > constant of the desired bit-masking
value.
< / p >
< / td >
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< / tr >
< tr >
< td >
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< p >
< code class = "literal" > sig_bits_fast< / code >
< / p >
< / td >
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< td >
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< p >
A < code class = "literal" > fast< / code > analog of < code class = "literal" > sig_bits< / code > .
< / p >
< / td >
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< / tr >
< tr >
< td >
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< p >
< code class = "literal" > bit_count< / code >
< / p >
< / td >
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< td >
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< p >
The value of the template parameter, in case its needed from a
renamed instantiation of the class template.
< / p >
< / td >
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< / tr >
< / tbody >
< / table > < / div >
< / div >
< br class = "table-break" >
< / div >
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< div class = "section" >
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< div class = "titlepage" > < div > < div > < h3 class = "title" >
< a name = "boost_integer.mask.implementation_notes" > < / a > < a class = "link" href = "mask.html#boost_integer.mask.implementation_notes" title = "Implementation Notes" > Implementation
Notes< / a >
< / h3 > < / div > < / div > < / div >
< p >
When < code class = "literal" > Bits< / code > is the exact size of a built-in unsigned type,
the implementation has to change to prevent undefined behavior. Therefore,
there are specializations of < code class = "literal" > low_bits_mask_t< / code > at those
bit counts.
< / p >
< / div >
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< div class = "section" >
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< div class = "titlepage" > < div > < div > < h3 class = "title" >
< a name = "boost_integer.mask.example" > < / a > < a class = "link" href = "mask.html#boost_integer.mask.example" title = "Example" > Example< / a >
< / h3 > < / div > < / div > < / div >
< pre class = "programlisting" > < span class = "preprocessor" > #include< / span > < span class = "special" > < < / span > < span class = "identifier" > boost< / span > < span class = "special" > /< / span > < span class = "identifier" > integer< / span > < span class = "special" > /< / span > < span class = "identifier" > integer_mask< / span > < span class = "special" > .< / span > < span class = "identifier" > hpp< / span > < span class = "special" > > < / span >
< span class = "comment" > //...
< / span >
< span class = "keyword" > int< / span > < span class = "identifier" > main< / span > < span class = "special" > ()< / span >
< span class = "special" > {< / span >
< span class = "keyword" > typedef< / span > < span class = "identifier" > boost< / span > < span class = "special" > ::< / span > < span class = "identifier" > high_bit_mask_t< / span > < span class = "special" > < < / span > < span class = "number" > 29< / span > < span class = "special" > > < / span > < span class = "identifier" > mask1_type< / span > < span class = "special" > ;< / span >
< span class = "keyword" > typedef< / span > < span class = "identifier" > boost< / span > < span class = "special" > ::< / span > < span class = "identifier" > low_bits_mask_t< / span > < span class = "special" > < < / span > < span class = "number" > 15< / span > < span class = "special" > > < / span > < span class = "identifier" > mask2_type< / span > < span class = "special" > ;< / span >
< span class = "identifier" > mask1_type< / span > < span class = "special" > ::< / span > < span class = "identifier" > least< / span > < span class = "identifier" > my_var1< / span > < span class = "special" > ;< / span >
< span class = "identifier" > mask2_type< / span > < span class = "special" > ::< / span > < span class = "identifier" > fast< / span > < span class = "identifier" > my_var2< / span > < span class = "special" > ;< / span >
< span class = "comment" > //...
< / span >
< span class = "identifier" > my_var1< / span > < span class = "special" > |=< / span > < span class = "identifier" > mask1_type< / span > < span class = "special" > ::< / span > < span class = "identifier" > high_bit< / span > < span class = "special" > ;< / span >
< span class = "identifier" > my_var2< / span > < span class = "special" > & =< / span > < span class = "identifier" > mask2_type< / span > < span class = "special" > ::< / span > < span class = "identifier" > sig_bits_fast< / span > < span class = "special" > ;< / span >
< span class = "comment" > //...
< / span > < span class = "special" > }< / span >
< / pre >
< / div >
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< div class = "section" >
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< div class = "titlepage" > < div > < div > < h3 class = "title" >
< a name = "boost_integer.mask.demonstration_program" > < / a > < a class = "link" href = "mask.html#boost_integer.mask.demonstration_program" title = "Demonstration Program" > Demonstration
Program< / a >
< / h3 > < / div > < / div > < / div >
< p >
The program < a href = "../../../test/integer_mask_test.cpp" target = "_top" > integer_mask_test.cpp< / a >
is a simplistic demonstration of the results from instantiating various examples
of the bit mask class templates.
< / p >
< / div >
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< div class = "section" >
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< div class = "titlepage" > < div > < div > < h3 class = "title" >
< a name = "boost_integer.mask.rationale" > < / a > < a class = "link" href = "mask.html#boost_integer.mask.rationale" title = "Rationale" > Rationale< / a >
< / h3 > < / div > < / div > < / div >
< p >
The class templates in this header are an extension of the < a class = "link" href = "integer.html" title = "Integer Type Selection" > integer
type selection class templates< / a > . The new class templates provide the
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same sized types, but also convenient masks to use when extracting the highest
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or all the significant bits when the containing built-in type contains more
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bits. This prevents contamination of values by the higher, unused bits.
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< div class = "section" >
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< div class = "titlepage" > < div > < div > < h3 class = "title" >
< a name = "boost_integer.mask.credits" > < / a > < a class = "link" href = "mask.html#boost_integer.mask.credits" title = "Credits" > Credits< / a >
< / h3 > < / div > < / div > < / div >
< p >
The author of the Boost bit mask class templates is < a href = "http://www.boost.org/people/daryle_walker.html" target = "_top" > Daryle
Walker< / a > .
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< td align = "right" > < div class = "copyright-footer" > Copyright © 2001 -2009 Beman Dawes, Daryle Walker, Gennaro Prota,
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John Maddock< p >
Distributed under the Boost Software License, Version 1.0. (See accompanying
file LICENSE_1_0.txt or copy at < a href = "http://www.boost.org/LICENSE_1_0.txt" target = "_top" > http://www.boost.org/LICENSE_1_0.txt< / a > )
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