From fa5aba353f61b3b889e25352a736585ffb88079f Mon Sep 17 00:00:00 2001 From: Gennaro Prota Date: Thu, 22 Jul 2004 08:57:45 +0000 Subject: [PATCH] - documented the new typedefs - added a what's new section - reformatted a bit - updated license reference [SVN r23944] --- doc/static_log2.html | 156 ++++++++++++++++++++++++++++++++++--------- 1 file changed, 124 insertions(+), 32 deletions(-) diff --git a/doc/static_log2.html b/doc/static_log2.html index 6764572..20fd8fe 100644 --- a/doc/static_log2.html +++ b/doc/static_log2.html @@ -1,73 +1,125 @@ + + + Binary Logarithm Template + + + +

c++boost.gif (8819 bytes)Binary Logarithm Template

+

The class template in <boost/integer/static_log2.hpp> determines the position of the highest bit in a given value. This facility is useful for solving generic programming problems.

+ +

Contents

+ + +

Synopsis

+ + 
+
 namespace boost
 {
 
-template < unsigned long Value >
-struct static_log2
-{
-    static const int  value = implementation_defined;
-};
+  typedef implementation-defined static_log2_argument_type;
+  typedef implementation-defined static_log2_result_type;
 
-template < >
-struct static_log2< 0ul >
-{
+  template < static_log2_argument_type arg >
+  struct static_log2
+  {
+    static const static_log2_result_type value = implementation-defined;
+  };
+
+
+  template < >
+  struct static_log2< 0 >
+  {
     // The logarithm of zero is undefined.
-};
+  };
+
 
 }  // namespace boost
+
+ + +

Usage

+ +

The boost::static_log2 class template takes one template -parameter, a value of type unsigned long. The template -only defines one member, value, that returns the truncated -base-two logarithm of the template parameter.

+parameter, a value of type static_log2_argument_type. The template +only defines one member, value, which gives the truncated +base-two logarithm of the template argument.

Since the logarithm of zero, for any base, is undefined, there is a -specialization of static_log2 for a template parameter +specialization of static_log2 for a template argument of zero. This specialization has no members, so an attempt to use the base-two logarithm of zero results in a compile-time error.

+

Note:

+ + +

Example

-
-#include <boost/integer/static_log2.hpp>
 
-template < unsigned long Value >
+
+
+
+#include "boost/integer/static_log2.hpp"
+
+
+template < boost::static_log2_argument_type value >
 bool is_it_what()
 {
-    typedef boost::static_log2<Value>  lb_type;
+    typedef boost::static_log2<value>  lb_type;
 
     int  temp = lb_type::value;
     //...
-
     return (temp % 2) != 0;
 }
 
@@ -77,47 +129,87 @@ int main()
 {
     bool  temp = is_it_what<2000>();
     //...
-
-    #if 0
+# if 0
     temp = is_it_what<0>();  // would give an error
-    #endif
+# endif
     //...
-
     temp = is_it_what<24>();
     //...
 }
+
 

 
+
+
 
Demonstration Program

 
+
+
 
The program static_log2_test.cpp
 is a simplistic demonstration of the results from instantiating various
 examples of the binary logarithm class template.

 
+
+
 
Rationale

 
+
+
 
The base-two (binary) logarithm, abbreviated lb, function
-is occasionally used to give order-estimates of computer algorithms. 
+is occasionally used to give order-estimates of computer algorithms.
 The truncated logarithm can be considered the highest power-of-two in a
 value, which corresponds to the value's highest set bit (for binary
 integers).  Sometimes the highest-bit position could be used in generic
 programming, which requires the position to be statically (i.e.
 at compile-time) available.

 
+
+
+
Changes from previous versions:

+
+
+
+
    
+
  • New in version 1.32.0:

    
+
+The argument type and the result type of boost::static_log2
+are now typedef'd. Formerly, they were hardcoded as unsigned long
+and int respectively. Please, use the provided typedefs in new
+code (and update old code as soon as possible).
+
    • 
+

+
+
+
 
Credits

 
-
The author of the Boost binary logarithm class template is Daryle Walker.  Giovanni Bajo
-added support for compilers without partial template specialization.

+
+
+
The original version of the Boost binary logarithm class template was
+written by Daryle Walker
+and then enhanced by Giovanni Bajo with support for compilers without
+partial template specialization. The current version was suggested,
+together with a reference implementation, by Vesa Karvonen. Gennaro Prota
+wrote the actual source file.
+

 
 

 
-
Revised May 14, 2002

 
-
© Copyright Daryle Walker 2001.  Permission to copy, use,
-modify, sell and distribute this document is granted provided this
-copyright notice appears in all copies.  This document is provided
-"as is" without express or implied warranty, and with no claim
-as to its suitability for any purpose.

+
+
Revised July 19, 2004

+
+          
© Copyright Daryle Walker 2001.

+             © Copyright Gennaro Prota 2004.

+
+     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)
+
+

+
 
+
 
+