std_bitset.h: Doxygenate std::bitset<>.

2002-04-12  Phil Edwards  <pme@gcc.gnu.org>

	* include/std/std_bitset.h:  Doxygenate std::bitset<>.  Clean up
	trailing spaces, indentation, and macro names.  Make exception
	messages more informative.

From-SVN: r52233

2 files changed, 497 insertions, 267 deletions

diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index 6533d39..b552f4f 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,3 +1,9 @@
+2002-04-12  Phil Edwards  <pme@gcc.gnu.org>
+
+	* include/std/std_bitset.h:  Doxygenate std::bitset<>.  Clean up
+	trailing spaces, indentation, and macro names.  Make exception
+	messages more informative.
+
 2002-04-11  Richard Henderson  <rth@redhat.com>
 
 	* include/bits/fstream.tcc (basic_filebuf<>::open): Fix & ordering.
diff --git a/libstdc++-v3/include/std/std_bitset.h b/libstdc++-v3/include/std/std_bitset.h
index a8aa319..bda3899 100644
--- a/libstdc++-v3/include/std/std_bitset.h
+++ b/libstdc++-v3/include/std/std_bitset.h
@@ -38,38 +38,29 @@
  * in supporting documentation.  Silicon Graphics makes no
  * representations about the suitability of this software for any
  * purpose.  It is provided "as is" without express or implied warranty.
- */ 
+ */
 
 /** @file bitset
  *  This is a Standard C++ Library header.  You should @c #include this header
  *  in your programs, rather than any of the "st[dl]_*.h" implementation files.
  */
 
-#ifndef __GLIBCPP_BITSET
-#define __GLIBCPP_BITSET
+#ifndef _GLIBCPP_BITSET_H
+#define _GLIBCPP_BITSET_H
 
 #pragma GCC system_header
 
-// A bitset of size N has N % (sizeof(unsigned long) * CHAR_BIT) unused 
-// bits.  (They are the high- order bits in the highest word.)  It is
-// a class invariant of class bitset<> that those unused bits are
-// always zero.
-
-// Most of the actual code isn't contained in bitset<> itself, but in the 
-// base class _Base_bitset.  The base class works with whole words, not with
-// individual bits.  This allows us to specialize _Base_bitset for the
-// important special case where the bitset is only a single word.
-
 #include <cstddef>     // for size_t
 #include <cstring>     // for memset
 #include <string>
-#include <bits/functexcept.h>   // for invalid_argument, out_of_range, 
-			         // overflow_error
+#include <bits/functexcept.h>   // for invalid_argument, out_of_range,
+                                // overflow_error
 #include <ostream>     // for ostream (operator<<)
 #include <istream>     // for istream (operator>>)
 
+
 #define _GLIBCPP_BITSET_BITS_PER_WORD (CHAR_BIT*sizeof(unsigned long))
-#define __BITSET_WORDS(__n) \
+#define _GLIBCPP_BITSET_WORDS(__n) \
  ((__n) < 1 ? 1 : ((__n) + _GLIBCPP_BITSET_BITS_PER_WORD - 1)/_GLIBCPP_BITSET_BITS_PER_WORD)
 
 namespace std
@@ -77,100 +68,107 @@ namespace std
   extern unsigned char 	_S_bit_count[256];
   extern unsigned char 	_S_first_one[256];
 
-  // Base class: general case.
+  /**
+   *  @if maint
+   *  Base class, general case.  It is a class inveriant that _Nw will be
+   *  nonnegative.
+   *
+   *  See documentation for bitset.
+   *  @endif
+  */
   template<size_t _Nw>
-    struct _Base_bitset 
+    struct _Base_bitset
     {
       typedef unsigned long _WordT;
 
-      // 0 is the least significant word.
-      _WordT 		_M_w[_Nw];                
-      
+      /// 0 is the least significant word.
+      _WordT 		_M_w[_Nw];
+
       _Base_bitset() { _M_do_reset(); }
-      _Base_bitset(unsigned long __val) 
+      _Base_bitset(unsigned long __val)
       {
 	_M_do_reset();
 	_M_w[0] = __val;
       }
 
-      static size_t 
+      static size_t
       _S_whichword(size_t __pos )
       { return __pos / _GLIBCPP_BITSET_BITS_PER_WORD; }
 
-      static size_t 
+      static size_t
       _S_whichbyte(size_t __pos )
       { return (__pos % _GLIBCPP_BITSET_BITS_PER_WORD) / CHAR_BIT; }
 
-      static size_t 
+      static size_t
       _S_whichbit(size_t __pos )
       { return __pos % _GLIBCPP_BITSET_BITS_PER_WORD; }
 
-      static _WordT 
+      static _WordT
       _S_maskbit(size_t __pos )
       { return (static_cast<_WordT>(1)) << _S_whichbit(__pos); }
 
-      _WordT& 
-      _M_getword(size_t __pos)       
+      _WordT&
+      _M_getword(size_t __pos)
       { return _M_w[_S_whichword(__pos)]; }
 
-      _WordT  
-      _M_getword(size_t __pos) const 
+      _WordT
+      _M_getword(size_t __pos) const
       { return _M_w[_S_whichword(__pos)]; }
 
-      _WordT& 
+      _WordT&
       _M_hiword() { return _M_w[_Nw - 1]; }
 
-      _WordT  
+      _WordT
       _M_hiword() const { return _M_w[_Nw - 1]; }
 
-      void 
-      _M_do_and(const _Base_bitset<_Nw>& __x) 
+      void
+      _M_do_and(const _Base_bitset<_Nw>& __x)
       {
-	for (size_t __i = 0; __i < _Nw; __i++) 
+	for (size_t __i = 0; __i < _Nw; __i++)
 	  _M_w[__i] &= __x._M_w[__i];
       }
 
-      void 
-      _M_do_or(const _Base_bitset<_Nw>& __x) 
+      void
+      _M_do_or(const _Base_bitset<_Nw>& __x)
       {
-	for (size_t __i = 0; __i < _Nw; __i++) 
+	for (size_t __i = 0; __i < _Nw; __i++)
 	  _M_w[__i] |= __x._M_w[__i];
       }
 
-      void 
-      _M_do_xor(const _Base_bitset<_Nw>& __x) 
+      void
+      _M_do_xor(const _Base_bitset<_Nw>& __x)
       {
 	for (size_t __i = 0; __i < _Nw; __i++)
 	  _M_w[__i] ^= __x._M_w[__i];
       }
 
-      void 
+      void
       _M_do_left_shift(size_t __shift);
 
-      void 
+      void
       _M_do_right_shift(size_t __shift);
-      
-      void 
-      _M_do_flip() 
+
+      void
+      _M_do_flip()
       {
-	for (size_t __i = 0; __i < _Nw; __i++) 
+	for (size_t __i = 0; __i < _Nw; __i++)
 	  _M_w[__i] = ~_M_w[__i];
       }
 
-      void 
-      _M_do_set() 
+      void
+      _M_do_set()
       {
 	for (size_t __i = 0; __i < _Nw; __i++)
 	  _M_w[__i] = ~static_cast<_WordT>(0);
       }
 
-      void 
+      void
       _M_do_reset() { memset(_M_w, 0, _Nw * sizeof(_WordT)); }
 
-      bool 
-      _M_is_equal(const _Base_bitset<_Nw>& __x) const 
+      bool
+      _M_is_equal(const _Base_bitset<_Nw>& __x) const
       {
-	for (size_t __i = 0; __i < _Nw; ++__i) 
+	for (size_t __i = 0; __i < _Nw; ++__i)
 	  {
 	    if (_M_w[__i] != __x._M_w[__i])
 	      return false;
@@ -178,10 +176,10 @@ namespace std
 	return true;
       }
 
-      bool 
-      _M_is_any() const 
+      bool
+      _M_is_any() const
       {
-	for (size_t __i = 0; __i < _Nw; __i++) 
+	for (size_t __i = 0; __i < _Nw; __i++)
 	  {
 	    if (_M_w[__i] != static_cast<_WordT>(0))
 	      return true;
@@ -189,14 +187,14 @@ namespace std
 	return false;
       }
 
-      size_t 
-      _M_do_count() const 
+      size_t
+      _M_do_count() const
       {
 	size_t __result = 0;
 	const unsigned char* __byte_ptr = (const unsigned char*)_M_w;
 	const unsigned char* __end_ptr = (const unsigned char*)(_M_w + _Nw);
-	
-	while ( __byte_ptr < __end_ptr ) 
+
+	while ( __byte_ptr < __end_ptr )
 	  {
 	    __result += _S_bit_count[*__byte_ptr];
 	    __byte_ptr++;
@@ -204,58 +202,58 @@ namespace std
 	return __result;
       }
 
-      unsigned long 
-      _M_do_to_ulong() const; 
+      unsigned long
+      _M_do_to_ulong() const;
 
       // find first "on" bit
-      size_t 
+      size_t
       _M_do_find_first(size_t __not_found) const;
 
       // find the next "on" bit that follows "prev"
-      size_t 
+      size_t
       _M_do_find_next(size_t __prev, size_t __not_found) const;
     };
 
   // Definitions of non-inline functions from _Base_bitset.
   template<size_t _Nw>
-    void 
-    _Base_bitset<_Nw>::_M_do_left_shift(size_t __shift) 
+    void
+    _Base_bitset<_Nw>::_M_do_left_shift(size_t __shift)
     {
-      if (__shift != 0) 
+      if (__shift != 0)
 	{
 	  const size_t __wshift = __shift / _GLIBCPP_BITSET_BITS_PER_WORD;
 	  const size_t __offset = __shift % _GLIBCPP_BITSET_BITS_PER_WORD;
-	  
+
 	  if (__offset == 0)
 	    for (size_t __n = _Nw - 1; __n >= __wshift; --__n)
 	      _M_w[__n] = _M_w[__n - __wshift];
-	  else 
+	  else
 	    {
 	      const size_t __sub_offset = _GLIBCPP_BITSET_BITS_PER_WORD - __offset;
 	      for (size_t __n = _Nw - 1; __n > __wshift; --__n)
-		_M_w[__n] = (_M_w[__n - __wshift] << __offset) | 
+		_M_w[__n] = (_M_w[__n - __wshift] << __offset) |
 		  (_M_w[__n - __wshift - 1] >> __sub_offset);
 	      _M_w[__wshift] = _M_w[0] << __offset;
 	    }
-	  
+
 	  fill(_M_w + 0, _M_w + __wshift, static_cast<_WordT>(0));
 	}
     }
-  
+
   template<size_t _Nw>
-    void 
-    _Base_bitset<_Nw>::_M_do_right_shift(size_t __shift) 
+    void
+    _Base_bitset<_Nw>::_M_do_right_shift(size_t __shift)
     {
-      if (__shift != 0) 
+      if (__shift != 0)
 	{
 	  const size_t __wshift = __shift / _GLIBCPP_BITSET_BITS_PER_WORD;
 	  const size_t __offset = __shift % _GLIBCPP_BITSET_BITS_PER_WORD;
 	  const size_t __limit = _Nw - __wshift - 1;
-	  
+
 	  if (__offset == 0)
 	    for (size_t __n = 0; __n <= __limit; ++__n)
 	      _M_w[__n] = _M_w[__n + __wshift];
-	  else 
+	  else
 	    {
 	      const size_t __sub_offset = _GLIBCPP_BITSET_BITS_PER_WORD - __offset;
 	      for (size_t __n = 0; __n < __limit; ++__n)
@@ -263,32 +261,32 @@ namespace std
 		  (_M_w[__n + __wshift + 1] << __sub_offset);
 	      _M_w[__limit] = _M_w[_Nw-1] >> __offset;
 	    }
-	  
+
 	  fill(_M_w + __limit + 1, _M_w + _Nw, static_cast<_WordT>(0));
 	}
     }
 
   template<size_t _Nw>
-    unsigned long 
+    unsigned long
     _Base_bitset<_Nw>::_M_do_to_ulong() const
     {
-      for (size_t __i = 1; __i < _Nw; ++__i) 
-	if (_M_w[__i]) 
-	  __throw_overflow_error("bitset");
+      for (size_t __i = 1; __i < _Nw; ++__i)
+	if (_M_w[__i])
+	  __throw_overflow_error("bitset -- too large to fit in unsigned long");
       return _M_w[0];
     }
 
   template<size_t _Nw>
-    size_t 
-    _Base_bitset<_Nw>::_M_do_find_first(size_t __not_found) const 
+    size_t
+    _Base_bitset<_Nw>::_M_do_find_first(size_t __not_found) const
     {
-      for (size_t __i = 0; __i < _Nw; __i++ ) 
+      for (size_t __i = 0; __i < _Nw; __i++ )
 	{
 	  _WordT __thisword = _M_w[__i];
-	  if ( __thisword != static_cast<_WordT>(0) ) 
+	  if ( __thisword != static_cast<_WordT>(0) )
 	    {
 	      // find byte within word
-	      for (size_t __j = 0; __j < sizeof(_WordT); __j++ ) 
+	      for (size_t __j = 0; __j < sizeof(_WordT); __j++ )
 		{
 		  unsigned char __this_byte
 		    = static_cast<unsigned char>(__thisword & (~(unsigned char)0));
@@ -307,22 +305,22 @@ namespace std
   template<size_t _Nw>
     size_t
     _Base_bitset<_Nw>::_M_do_find_next(size_t __prev, size_t __not_found) const
-    { 
+    {
       // make bound inclusive
       ++__prev;
-      
+
       // check out of bounds
       if ( __prev >= _Nw * _GLIBCPP_BITSET_BITS_PER_WORD )
 	return __not_found;
-      
+
       // search first word
       size_t __i = _S_whichword(__prev);
       _WordT __thisword = _M_w[__i];
-      
+
       // mask off bits below bound
       __thisword &= (~static_cast<_WordT>(0)) << _S_whichbit(__prev);
-      
-      if ( __thisword != static_cast<_WordT>(0) ) 
+
+      if ( __thisword != static_cast<_WordT>(0) )
 	{
 	  // find byte within word
 	  // get first byte into place
@@ -334,27 +332,27 @@ namespace std
 	      if ( __this_byte )
 		return __i*_GLIBCPP_BITSET_BITS_PER_WORD + __j*CHAR_BIT +
 		  _S_first_one[__this_byte];
-	      
+
 	      __thisword >>= CHAR_BIT;
 	    }
 	}
-      
+
       // check subsequent words
       __i++;
-      for ( ; __i < _Nw; __i++ ) 
+      for ( ; __i < _Nw; __i++ )
 	{
 	  __thisword = _M_w[__i];
-	  if ( __thisword != static_cast<_WordT>(0) ) 
+	  if ( __thisword != static_cast<_WordT>(0) )
 	    {
 	      // find byte within word
-	      for (size_t __j = 0; __j < sizeof(_WordT); __j++ ) 
+	      for (size_t __j = 0; __j < sizeof(_WordT); __j++ )
 		{
 		  unsigned char __this_byte
 		    = static_cast<unsigned char>(__thisword & (~(unsigned char)0));
 		  if ( __this_byte )
 		    return __i*_GLIBCPP_BITSET_BITS_PER_WORD + __j*CHAR_BIT +
 		      _S_first_one[__this_byte];
-		  
+
 		  __thisword >>= CHAR_BIT;
 		}
 	    }
@@ -362,11 +360,17 @@ namespace std
       // not found, so return an indication of failure.
       return __not_found;
     } // end _M_do_find_next
-  
 
-  // Base class: specialization for a single word.
-  template<> 
-    struct _Base_bitset<1> 
+
+  /**
+   *  @if maint
+   *  Base class, specialization for a single word.
+   *
+   *  See documentation for bitset.
+   *  @endif
+  */
+  template<>
+    struct _Base_bitset<1>
     {
       typedef unsigned long _WordT;
       _WordT _M_w;
@@ -374,73 +378,73 @@ namespace std
       _Base_bitset( void ) : _M_w(0) {}
       _Base_bitset(unsigned long __val) : _M_w(__val) {}
 
-      static size_t 
+      static size_t
       _S_whichword(size_t __pos )
       { return __pos / _GLIBCPP_BITSET_BITS_PER_WORD; }
 
-      static size_t 
+      static size_t
       _S_whichbyte(size_t __pos )
       { return (__pos % _GLIBCPP_BITSET_BITS_PER_WORD) / CHAR_BIT; }
 
-      static size_t 
+      static size_t
       _S_whichbit(size_t __pos )
       {  return __pos % _GLIBCPP_BITSET_BITS_PER_WORD; }
 
-      static _WordT 
+      static _WordT
       _S_maskbit(size_t __pos )
       { return (static_cast<_WordT>(1)) << _S_whichbit(__pos); }
 
-      _WordT& 
+      _WordT&
       _M_getword(size_t) { return _M_w; }
 
-      _WordT  
+      _WordT
       _M_getword(size_t) const { return _M_w; }
 
-      _WordT& 
+      _WordT&
       _M_hiword() { return _M_w; }
 
-      _WordT  
+      _WordT
       _M_hiword() const { return _M_w; }
 
-      void 
+      void
       _M_do_and(const _Base_bitset<1>& __x) { _M_w &= __x._M_w; }
 
-      void 
+      void
       _M_do_or(const _Base_bitset<1>& __x)  { _M_w |= __x._M_w; }
 
-      void 
+      void
       _M_do_xor(const _Base_bitset<1>& __x) { _M_w ^= __x._M_w; }
 
-      void 
+      void
       _M_do_left_shift(size_t __shift) { _M_w <<= __shift; }
 
-      void 
+      void
       _M_do_right_shift(size_t __shift) { _M_w >>= __shift; }
 
-      void 
+      void
       _M_do_flip() { _M_w = ~_M_w; }
 
-      void 
+      void
       _M_do_set() { _M_w = ~static_cast<_WordT>(0); }
 
-      void 
+      void
       _M_do_reset() { _M_w = 0; }
 
-      bool 
+      bool
       _M_is_equal(const _Base_bitset<1>& __x) const
       { return _M_w == __x._M_w; }
 
-      bool 
+      bool
       _M_is_any() const { return _M_w != 0; }
 
-      size_t 
-      _M_do_count() const 
+      size_t
+      _M_do_count() const
       {
 	size_t __result = 0;
 	const unsigned char* __byte_ptr = (const unsigned char*)&_M_w;
 	const unsigned char* __end_ptr
 	  = ((const unsigned char*)&_M_w)+sizeof(_M_w);
-	while ( __byte_ptr < __end_ptr ) 
+	while ( __byte_ptr < __end_ptr )
 	  {
 	    __result += _S_bit_count[*__byte_ptr];
 	    __byte_ptr++;
@@ -448,61 +452,128 @@ namespace std
 	return __result;
       }
 
-      unsigned long 
+      unsigned long
       _M_do_to_ulong() const { return _M_w; }
 
-      size_t 
+      size_t
       _M_do_find_first(size_t __not_found) const;
 
       // find the next "on" bit that follows "prev"
       size_t
-      _M_do_find_next(size_t __prev, size_t __not_found) const; 
+      _M_do_find_next(size_t __prev, size_t __not_found) const;
     };
 
   // Helper class to zero out the unused high-order bits in the highest word.
-  template<size_t _Extrabits> 
-    struct _Sanitize 
+  template<size_t _Extrabits>
+    struct _Sanitize
     {
       static void _S_do_sanitize(unsigned long& __val)
       { __val &= ~((~static_cast<unsigned long>(0)) << _Extrabits); }
     };
 
-  template<> 
-    struct _Sanitize<0> 
+  template<>
+    struct _Sanitize<0>
     { static void _S_do_sanitize(unsigned long) { } };
 
-  // Class bitset.
-  // _Nb may be any nonzero number of type size_t.
+  /**
+   *  @brief  The %bitset class represents a @e fixed-size sequence of bits.
+   *
+   *  @ingroup Containers
+   *
+   *  Meets the requirements of a <a href="tables.html#65">container</a>.
+   *
+   *  The template argument, @a _Nb, may be any nonzero number of type
+   *  size_t.
+   *
+   *  A %bitset of size N has N % (sizeof(unsigned long) * CHAR_BIT) unused
+   *  bits.  (They are the high-order bits in the highest word.)  It is
+   *  a class invariant that those unused bits are always zero.
+   *
+   *  If you think of %bitset as "a simple array of bits," be aware that
+   *  your mental picture is reversed:  a %bitset behaves the same way as
+   *  bits in integers do, with the bit at index 0 in the "least significant
+   *  / right-hand" position, and the bit at index N-1 in the "most
+   *  significant / left-hand" position.  Thus, unlike other containers, a
+   *  %bitset's index "counts from right to left," to put it very loosely.
+   *
+   *  This behavior is preserved when translating to and from strings.  For
+   *  example, the first line of the following program probably prints
+   *  "b('a') is 0001100001" on a modern ASCII system.
+   *
+   *  @code
+   *     #include <bitset>
+   *     #include <iostream>
+   *     #include <sstream>
+   *
+   *     using namespace std;
+   *
+   *     int main()
+   *     {
+   *         long         a = 'a';
+   *         bitset<10>   b(a);
+   *
+   *         cout << "b('a') is " << b << endl;
+   *
+   *         ostringstream s;
+   *         s << b;
+   *         string  str = s.str();
+   *         cout << "index 3 in the string is " << str[3] << " but\n"
+   *              << "index 3 in the bitset is " << b[3] << endl;
+   *     }
+   *  @endcode
+   *
+   *  Also see http://gcc.gnu.org/onlinedocs/libstdc++/ext/sgiexts.html#ch23
+   *
+   *  @if maint
+   *  Most of the actual code isn't contained in %bitset<> itself, but in the
+   *  base class _Base_bitset.  The base class works with whole words, not with
+   *  individual bits.  This allows us to specialize _Base_bitset for the
+   *  important special case where the %bitset is only a single word.
+   *
+   *  Extra confusion can result due to the fact that the storage for
+   *  _Base_bitset @e is a regular array, and is indexed as such.  This is
+   *  carefully encapsulated.
+   *  @endif
+  */
   template<size_t _Nb>
-    class bitset : private _Base_bitset<__BITSET_WORDS(_Nb)>
+    class bitset : private _Base_bitset<_GLIBCPP_BITSET_WORDS(_Nb)>
   {
   private:
-    typedef _Base_bitset<__BITSET_WORDS(_Nb)> _Base;
+    typedef _Base_bitset<_GLIBCPP_BITSET_WORDS(_Nb)> _Base;
     typedef unsigned long _WordT;
-    
-    void 
-    _M_do_sanitize() 
+
+    void
+    _M_do_sanitize()
     {
-    _Sanitize<_Nb%_GLIBCPP_BITSET_BITS_PER_WORD>::_S_do_sanitize(this->_M_hiword());
+      _Sanitize<_Nb%_GLIBCPP_BITSET_BITS_PER_WORD>::
+          _S_do_sanitize(this->_M_hiword());
     }
 
   public:
-    // bit reference:
-    class reference;
-    friend class reference;
-    
-    class reference 
+    /**
+     *  This encapsulates the concept of a single bit.  An instance of this
+     *  class is a proxy for an actual bit; this way the individual bit
+     *  operations are done as faster word-size bitwise instructions.
+     *
+     *  Most users will never need to use this class directly; conversions
+     *  to and from bool are automatic and should be transparent.  Overloaded
+     *  operators help to preserve the illusion.
+     *
+     *  (On a typical system, this "bit %reference" is 64 times the size of
+     *  an actual bit.  Ha.)
+    */
+    class reference
     {
       friend class bitset;
-      
+
       _WordT *_M_wp;
       size_t _M_bpos;
-      
+
       // left undefined
       reference();
-      
+
     public:
-      reference( bitset& __b, size_t __pos ) 
+      reference(bitset& __b, size_t __pos)
       {
 	_M_wp = &__b._M_getword(__pos);
 	_M_bpos = _Base::_S_whichbit(__pos);
@@ -511,8 +582,8 @@ namespace std
       ~reference() { }
 
       // for b[i] = __x;
-      reference& 
-      operator=(bool __x) 
+      reference&
+      operator=(bool __x)
       {
 	if ( __x )
 	  *_M_wp |= _Base::_S_maskbit(_M_bpos);
@@ -520,10 +591,10 @@ namespace std
 	  *_M_wp &= ~_Base::_S_maskbit(_M_bpos);
 	return *this;
       }
-      
+
       // for b[i] = b[__j];
-      reference& 
-      operator=(const reference& __j) 
+      reference&
+      operator=(const reference& __j)
       {
 	if ( (*(__j._M_wp) & _Base::_S_maskbit(__j._M_bpos)) )
 	  *_M_wp |= _Base::_S_maskbit(_M_bpos);
@@ -533,7 +604,7 @@ namespace std
       }
 
       // flips the bit
-      bool 
+      bool
       operator~() const
       { return (*(_M_wp) & _Base::_S_maskbit(_M_bpos)) == 0; }
 
@@ -542,88 +613,131 @@ namespace std
       { return (*(_M_wp) & _Base::_S_maskbit(_M_bpos)) != 0; }
 
       // for b[i].flip();
-      reference& 
-      flip() 
+      reference&
+      flip()
       {
 	*_M_wp ^= _Base::_S_maskbit(_M_bpos);
 	return *this;
       }
     };
-    
+    friend class reference;
+
     // 23.3.5.1 constructors:
+    /// All bits set to zero.
     bitset() { }
 
-    bitset(unsigned long __val) : _Base_bitset<__BITSET_WORDS(_Nb)>(__val) 
+    /// Initial bits bitwise-copied from a single word (others set to zero).
+    bitset(unsigned long __val) : _Base(__val)
     { _M_do_sanitize(); }
 
+    /**
+     *  @brief  Use a subset of a string.
+     *  @param  s  A string of '0' and '1' characters.
+     *  @param  pos  Index of the first character in @a s to use; defaults
+     *               to zero.
+     *  @throw  std::out_of_range  If @a pos is bigger the size of @a s.
+     *  @throw  std::invalid_argument  If a character appears in the string
+     *                                 which is neither '0' nor '1'.
+    */
     template<class _CharT, class _Traits, class _Alloc>
       explicit bitset(const basic_string<_CharT, _Traits, _Alloc>& __s,
-		      size_t __pos = 0) : _Base() 
+		      size_t __pos = 0) : _Base()
       {
-	if (__pos > __s.size()) 
-	  __throw_out_of_range("bitset");
+	if (__pos > __s.size())
+	  __throw_out_of_range("bitset -- initial position is larger than "
+	                       "the string itself");
 	_M_copy_from_string(__s, __pos,
 			    basic_string<_CharT, _Traits, _Alloc>::npos);
       }
 
+    /**
+     *  @brief  Use a subset of a string.
+     *  @param  s  A string of '0' and '1' characters.
+     *  @param  pos  Index of the first character in @a s to use.
+     *  @param  n    The number of characters to copy.
+     *  @throw  std::out_of_range  If @a pos is bigger the size of @a s.
+     *  @throw  std::invalid_argument  If a character appears in the string
+     *                                 which is neither '0' nor '1'.
+    */
     template<class _CharT, class _Traits, class _Alloc>
       bitset(const basic_string<_CharT, _Traits, _Alloc>& __s,
-	     size_t __pos, size_t __n) : _Base() 
+	     size_t __pos, size_t __n) : _Base()
       {
-	if (__pos > __s.size()) 
-	  __throw_out_of_range("bitset");
+	if (__pos > __s.size())
+	  __throw_out_of_range("bitset -- initial position is larger than "
+	                       "the string itself");
 	_M_copy_from_string(__s, __pos, __n);
       }
 
     // 23.3.5.2 bitset operations:
-    bitset<_Nb>& 
-    operator&=(const bitset<_Nb>& __rhs) 
+    //@{
+    /**
+     *  @brief  Operations on bitsets.
+     *  @param  rhs  A same-sized bitset.
+     *
+     *  These should be self-explanatory.
+    */
+    bitset<_Nb>&
+    operator&=(const bitset<_Nb>& __rhs)
     {
       this->_M_do_and(__rhs);
       return *this;
     }
 
-    bitset<_Nb>& 
-    operator|=(const bitset<_Nb>& __rhs) 
+    bitset<_Nb>&
+    operator|=(const bitset<_Nb>& __rhs)
     {
       this->_M_do_or(__rhs);
       return *this;
     }
 
-    bitset<_Nb>& 
-    operator^=(const bitset<_Nb>& __rhs) 
+    bitset<_Nb>&
+    operator^=(const bitset<_Nb>& __rhs)
     {
       this->_M_do_xor(__rhs);
       return *this;
     }
-
-    bitset<_Nb>& 
-    operator<<=(size_t __pos) 
+    //@}
+
+    //@{
+    /**
+     *  @brief  Operations on bitsets.
+     *  @param  pos  The number of places to shift.
+     *
+     *  These should be self-explanatory.
+    */
+    bitset<_Nb>&
+    operator<<=(size_t __pos)
     {
       this->_M_do_left_shift(__pos);
       this->_M_do_sanitize();
       return *this;
     }
 
-    bitset<_Nb>& 
-    operator>>=(size_t __pos) 
+    bitset<_Nb>&
+    operator>>=(size_t __pos)
     {
       this->_M_do_right_shift(__pos);
       this->_M_do_sanitize();
       return *this;
     }
-
-    // Extension:
-    // Versions of single-bit set, reset, flip, test with no range checking.
-    bitset<_Nb>& 
-    _Unchecked_set(size_t __pos) 
+    //@}
+
+    //@{
+    /**
+     *  These versions of single-bit set, reset, flip, and test are
+     *  extensions from the SGI version.  They do no range checking.
+     *  @ingroup SGIextensions
+    */
+    bitset<_Nb>&
+    _Unchecked_set(size_t __pos)
     {
       this->_M_getword(__pos) |= _Base::_S_maskbit(__pos);
       return *this;
     }
 
-    bitset<_Nb>& 
-    _Unchecked_set(size_t __pos, int __val) 
+    bitset<_Nb>&
+    _Unchecked_set(size_t __pos, int __val)
     {
       if (__val)
 	this->_M_getword(__pos) |= _Base::_S_maskbit(__pos);
@@ -632,95 +746,157 @@ namespace std
       return *this;
     }
 
-    bitset<_Nb>& 
-    _Unchecked_reset(size_t __pos) 
+    bitset<_Nb>&
+    _Unchecked_reset(size_t __pos)
     {
       this->_M_getword(__pos) &= ~_Base::_S_maskbit(__pos);
       return *this;
     }
 
-    bitset<_Nb>& 
-    _Unchecked_flip(size_t __pos) 
+    bitset<_Nb>&
+    _Unchecked_flip(size_t __pos)
     {
       this->_M_getword(__pos) ^= _Base::_S_maskbit(__pos);
       return *this;
     }
 
-    bool 
-    _Unchecked_test(size_t __pos) const 
+    bool
+    _Unchecked_test(size_t __pos) const
     {
-      return (this->_M_getword(__pos) & _Base::_S_maskbit(__pos)) 
+      return (this->_M_getword(__pos) & _Base::_S_maskbit(__pos))
 	!= static_cast<_WordT>(0);
     }
+    //@}
 
     // Set, reset, and flip.
-    bitset<_Nb>& 
-    set() 
+    /**
+     *  @brief Sets every bit to true.
+    */
+    bitset<_Nb>&
+    set()
     {
       this->_M_do_set();
       this->_M_do_sanitize();
       return *this;
     }
 
-    bitset<_Nb>& 
-    set(size_t __pos, bool __val = true) 
+    /**
+     *  @brief Sets a given bit to a particular value.
+     *  @param  pos  The index of the bit.
+     *  @param  val  Either true or false, defaults to true.
+     *  @throw  std::out_of_range  If @a pos is bigger the size of the %set.
+    */
+    bitset<_Nb>&
+    set(size_t __pos, bool __val = true)
     {
       if (__pos >= _Nb)
-	__throw_out_of_range("bitset");
+	__throw_out_of_range("bitset -- set() argument too large");
       return _Unchecked_set(__pos, __val);
     }
 
-    bitset<_Nb>& 
-    reset() 
+    /**
+     *  @brief Sets every bit to false.
+    */
+    bitset<_Nb>&
+    reset()
     {
       this->_M_do_reset();
       return *this;
     }
 
-    bitset<_Nb>& 
-    reset(size_t __pos) 
+    /**
+     *  @brief Sets a given bit to false.
+     *  @param  pos  The index of the bit.
+     *  @throw  std::out_of_range  If @a pos is bigger the size of the %set.
+     *
+     *  Same as writing @c set(pos,false).
+    */
+    bitset<_Nb>&
+    reset(size_t __pos)
     {
       if (__pos >= _Nb)
-	__throw_out_of_range("bitset");
+	__throw_out_of_range("bitset -- reset() argument too large");
       return _Unchecked_reset(__pos);
     }
 
-    bitset<_Nb>& 
-    flip() 
+    /**
+     *  @brief Toggles every bit to its opposite value.
+    */
+    bitset<_Nb>&
+    flip()
     {
       this->_M_do_flip();
       this->_M_do_sanitize();
       return *this;
     }
 
-    bitset<_Nb>& 
-    flip(size_t __pos) 
+    /**
+     *  @brief Toggles a given bit to its opposite value.
+     *  @param  pos  The index of the bit.
+     *  @throw  std::out_of_range  If @a pos is bigger the size of the %set.
+    */
+    bitset<_Nb>&
+    flip(size_t __pos)
     {
       if (__pos >= _Nb)
-	__throw_out_of_range("bitset");
+	__throw_out_of_range("bitset -- flip() argument too large");
       return _Unchecked_flip(__pos);
     }
 
-    bitset<_Nb> 
+    /// See the no-argument flip().
+    bitset<_Nb>
     operator~() const { return bitset<_Nb>(*this).flip(); }
 
-    // element access:
-    //for b[i];
-    // _GLIBCPP_RESOLVE_LIB_DEFECTS Note that this implementation already
-    // resolves DR 11 (items 1 and 2), but does not do the range-checking
-    // required by that DR's resolution.  -pme
-    reference 
+    //@{
+    /**
+     *  @brief  Array-indexing support.
+     *  @param  pos  Index into the %bitset.
+     *  @return  A bool for a 'const %bitset'.  For non-const bitsets, an
+     *           instance of the reference proxy class.
+     *  @note  These operators do no range checking and throw no exceptions,
+     *         as required by DR 11 to the standard.
+     *
+     *  @if maint
+     *  _GLIBCPP_RESOLVE_LIB_DEFECTS Note that this implementation already
+     *  resolves DR 11 (items 1 and 2), but does not do the range-checking
+     *  required by that DR's resolution.  -pme
+     *  The DR has since been changed:  range-checking is a precondition
+     *  (users' responsibility), and these functions must not throw.  -pme
+     *  @endif
+    */
+    reference
     operator[](size_t __pos) { return reference(*this,__pos); }
 
-    bool 
+    bool
     operator[](size_t __pos) const { return _Unchecked_test(__pos); }
-
-    unsigned long 
+    //@}
+
+    /**
+     *  @brief Retuns a numerical interpretation of the %bitset.
+     *  @return  The integral equivalent of the bits.
+     *  @throw  std::overflow_error  If there are too many bits to be
+     *                               represented in an @c unsigned @c long.
+    */
+    unsigned long
     to_ulong() const { return this->_M_do_to_ulong(); }
 
+    /**
+     *  @brief Retuns a character interpretation of the %bitset.
+     *  @return  The string equivalent of the bits.
+     *
+     *  Note the ordering of the bits:  decreasing character positions
+     *  correspond to increasing bit positions (see the main class notes for
+     *  an example).
+     *
+     *  Also note that you must specify the string's template parameters
+     *  explicitly.  Given a bitset @c bs and a string @s:
+     *  @code
+     *     s = bs.to_string<char,char_traits<char>,allocator<char> >();
+     *  @endcode
+    */
     template<class _CharT, class _Traits, class _Alloc>
-      basic_string<_CharT, _Traits, _Alloc> 
-      to_string() const 
+      basic_string<_CharT, _Traits, _Alloc>
+      to_string() const
       {
 	basic_string<_CharT, _Traits, _Alloc> __result;
 	_M_copy_to_string(__result);
@@ -729,76 +905,103 @@ namespace std
 
     // Helper functions for string operations.
     template<class _CharT, class _Traits, class _Alloc>
-      void 
+      void
       _M_copy_from_string(const basic_string<_CharT,_Traits,_Alloc>& __s,
                           size_t, size_t);
 
     template<class _CharT, class _Traits, class _Alloc>
-      void 
+      void
       _M_copy_to_string(basic_string<_CharT,_Traits,_Alloc>&) const;
 
-    size_t 
+    /// Returns the number of bits which are set.
+    size_t
     count() const { return this->_M_do_count(); }
 
-    size_t 
+    /// Returns the total number of bits.
+    size_t
     size() const { return _Nb; }
 
-    bool 
-    operator==(const bitset<_Nb>& __rhs) const 
+    //@{
+    /// These comparisons for equality/inequality are, well, @e bitwise.
+    bool
+    operator==(const bitset<_Nb>& __rhs) const
     { return this->_M_is_equal(__rhs); }
 
-    bool 
-    operator!=(const bitset<_Nb>& __rhs) const 
+    bool
+    operator!=(const bitset<_Nb>& __rhs) const
     { return !this->_M_is_equal(__rhs); }
-
-    bool 
-    test(size_t __pos) const 
+    //@}
+
+    /**
+     *  @brief Tests the value of a bit.
+     *  @param  pos  The index of a bit.
+     *  @return  The value at @a pos.
+     *  @throw  std::out_of_range  If @a pos is bigger the size of the %set.
+    */
+    bool
+    test(size_t __pos) const
     {
       if (__pos >= _Nb)
-	__throw_out_of_range("bitset");
+	__throw_out_of_range("bitset -- test() argument too large");
       return _Unchecked_test(__pos);
     }
 
-    bool 
+    /**
+     *  @brief Tests whether any of the bits are on.
+     *  @return  True if at least one bit is set.
+    */
+    bool
     any() const { return this->_M_is_any(); }
 
-    bool 
+    /**
+     *  @brief Tests whether any of the bits are on.
+     *  @return  True if none of the bits are set.
+    */
+    bool
     none() const { return !this->_M_is_any(); }
 
-    bitset<_Nb> 
+    //@{
+    /// Self-explanatory.
+    bitset<_Nb>
     operator<<(size_t __pos) const
     { return bitset<_Nb>(*this) <<= __pos; }
 
-    bitset<_Nb> 
+    bitset<_Nb>
     operator>>(size_t __pos) const
     { return bitset<_Nb>(*this) >>= __pos; }
+    //@}
 
-    // EXTENSIONS: bit-find operations.  These operations are
-    // experimental, and are subject to change or removal in future
-    // versions.
-
-    // find the index of the first "on" bit
-    size_t 
-    _Find_first() const 
+    /**
+     *  @brief  Finds the index of the first "on" bit.
+     *  @ingroup SGIextensions
+     *  @sa  _Find_next
+    */
+    size_t
+    _Find_first() const
     { return this->_M_do_find_first(_Nb); }
 
-    // find the index of the next "on" bit after prev
-    size_t 
-    _Find_next(size_t __prev ) const 
+    /**
+     *  @brief  Finds the index of the next "on" bit after prev.
+     *  @param  prev  Where to start searching.
+     *  @ingroup SGIextensions
+     *  @sa  _Find_first
+    */
+    size_t
+    _Find_next(size_t __prev ) const
     { return this->_M_do_find_next(__prev, _Nb); }
   };
 
   // Definitions of non-inline member functions.
   template<size_t _Nb>
     template<class _CharT, class _Traits, class _Alloc>
-    void 
+    void
     bitset<_Nb>::_M_copy_from_string(const basic_string<_CharT,_Traits,_Alloc>& __s, size_t __pos, size_t __n)
-    {  
+    {
       reset();
       const size_t __nbits = min(_Nb, min(__n, __s.size() - __pos));
-      for (size_t __i = 0; __i < __nbits; ++__i) 
+      for (size_t __i = 0; __i < __nbits; ++__i)
 	{
-	  switch(__s[__pos + __nbits - __i - 1]) 
+	  switch(__s[__pos + __nbits - __i - 1])
 	    {
 	    case '0':
 	      break;
@@ -806,26 +1009,36 @@ namespace std
 	      set(__i);
 	      break;
 	    default:
-	      __throw_invalid_argument("bitset");
+	      __throw_invalid_argument("bitset -- string contains characters "
+	                               "which are neither 0 nor 1");
 	    }
 	}
     }
 
   template<size_t _Nb>
     template<class _CharT, class _Traits, class _Alloc>
-    void 
+    void
     bitset<_Nb>::_M_copy_to_string(basic_string<_CharT, _Traits, _Alloc>& __s) const
     {
       __s.assign(_Nb, '0');
-      for (size_t __i = 0; __i < _Nb; ++__i) 
+      for (size_t __i = 0; __i < _Nb; ++__i)
 	if (_Unchecked_test(__i))
 	  __s[_Nb - 1 - __i] = '1';
     }
 
   // 23.3.5.3 bitset operations:
+  //@{
+  /**
+   *  @brief  Global bitwise operations on bitsets.
+   *  @param  x  A bitset.
+   *  @param  y  A bitset of the same size as @a x.
+   *  @return  A new bitset.
+   *
+   *  These should be self-explanatory.
+  */
   template<size_t _Nb>
-    inline bitset<_Nb> 
-    operator&(const bitset<_Nb>& __x, const bitset<_Nb>& __y) 
+    inline bitset<_Nb>
+    operator&(const bitset<_Nb>& __x, const bitset<_Nb>& __y)
     {
       bitset<_Nb> __result(__x);
       __result &= __y;
@@ -833,8 +1046,8 @@ namespace std
     }
 
   template<size_t _Nb>
-    inline bitset<_Nb> 
-    operator|(const bitset<_Nb>& __x, const bitset<_Nb>& __y) 
+    inline bitset<_Nb>
+    operator|(const bitset<_Nb>& __x, const bitset<_Nb>& __y)
     {
       bitset<_Nb> __result(__x);
       __result |= __y;
@@ -842,14 +1055,24 @@ namespace std
     }
 
   template <size_t _Nb>
-    inline bitset<_Nb> 
-    operator^(const bitset<_Nb>& __x, const bitset<_Nb>& __y) 
+    inline bitset<_Nb>
+    operator^(const bitset<_Nb>& __x, const bitset<_Nb>& __y)
     {
       bitset<_Nb> __result(__x);
       __result ^= __y;
       return __result;
     }
-
+  //@}
+
+  //@{
+  /**
+   *  @brief Global I/O operators for bitsets.
+   *
+   *  Direct I/O between streams and bitsets is supported.  Output is
+   *  straightforward.  Input will skip whitespace, only accept '0' and '1'
+   *  characters, and will only extract as many digits as the %bitset will
+   *  hold.
+  */
   template<class _CharT, class _Traits, size_t _Nb>
     basic_istream<_CharT, _Traits>&
     operator>>(basic_istream<_CharT, _Traits>& __is, bitset<_Nb>& __x)
@@ -857,38 +1080,38 @@ namespace std
       typedef typename _Traits::char_type char_type;
       basic_string<_CharT, _Traits> __tmp;
       __tmp.reserve(_Nb);
-      
+
       // Skip whitespace
       typename basic_istream<_CharT, _Traits>::sentry __sentry(__is);
-      if (__sentry) 
+      if (__sentry)
 	{
 	  basic_streambuf<_CharT, _Traits>* __buf = __is.rdbuf();
-	  for (size_t __i = 0; __i < _Nb; ++__i) 
+	  for (size_t __i = 0; __i < _Nb; ++__i)
 	    {
 	      static typename _Traits::int_type __eof = _Traits::eof();
-	      
+
 	      typename _Traits::int_type __c1 = __buf->sbumpc();
-	      if (_Traits::eq_int_type(__c1, __eof)) 
+	      if (_Traits::eq_int_type(__c1, __eof))
 		{
 		  __is.setstate(ios_base::eofbit);
 		  break;
 		}
-	      else 
+	      else
 		{
 		  char_type __c2 = _Traits::to_char_type(__c1);
 		  char_type __c  = __is.narrow(__c2, '*');
-		  
+
 		  if (__c == '0' || __c == '1')
 		    __tmp.push_back(__c);
-		  else if (_Traits::eq_int_type(__buf->sputbackc(__c2), 
-						__eof)) 
+		  else if (_Traits::eq_int_type(__buf->sputbackc(__c2),
+						__eof))
 		    {
 		      __is.setstate(ios_base::failbit);
 		      break;
 		    }
 		}
 	    }
-	  
+
 	  if (__tmp.empty())
 	    __is.setstate(ios_base::failbit);
 	  else
@@ -906,8 +1129,9 @@ namespace std
       __x._M_copy_to_string(__tmp);
       return __os << __tmp;
     }
+  //@}
 } // namespace std
 
-#undef __BITSET_WORDS
+#undef _GLIBCPP_BITSET_WORDS
 
-#endif 
+#endif /* _GLIBCPP_BITSET_H */