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< div class = "section" title = "Integer Masks" >
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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" title = "Overview" >
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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" title = "Synopsis" >
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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" title = "Single Bit-Mask Class Template" >
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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" title = "Group Bit-Mask Class Template" >
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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" title = "Implementation Notes" >
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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" title = "Example" >
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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" title = "Demonstration Program" >
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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" title = "Rationale" >
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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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</ p >
</ div >
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< div class = "section" title = "Credits" >
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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 > .
</ p >
</ div >
</ div >
< table xmlns:rev = "http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width = "100%" >< tr >
< td align = "left" ></ td >
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2009-11-25 12:38:09 +00:00
John Maddock< p >
Distributed under the Boost Software License, Version 1.0. (See accompanying
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