Avoids std::distance calls

[François Dumont <frs dot dumont at gmail dot com>]

Hi

I'd like to propose this patch to avoid std::distance calls. In a number 
of situation in algos we already have the size of the buffer we need so 
we shouldn't have to compute it again.

I don't think there is any abi concern for this inline constructor, 
isn't there ?

    * include/bits/stl_tempbuf.h
    (_Temporary_buffer(_FwdIte, _FwdIte)): Delete, replaced by...
    (_Temporary_buffer(_FwdIte, size_type)): ...this, new.
    * include/ext/memory (temporary_buffer<>(_FwdIte, _FwdIte)): Adapt.
    * include/bits/stl_algo.h (__stable_partition): Adapt.
    (__inplace_merge): Adapt.
    (__stable_sort): Adapt.

Tested under Linux x86_64 normal mode.

Ok to commit ?

François

diff --git a/libstdc++-v3/include/bits/stl_algo.h b/libstdc++-v3/include/bits/stl_algo.h
index 914a6b6..d8488a7 100644
--- a/libstdc++-v3/include/bits/stl_algo.h
+++ b/libstdc++-v3/include/bits/stl_algo.h
@@ -1615,7 +1615,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       typedef typename iterator_traits<_ForwardIterator>::difference_type
 	_DistanceType;
 
-      _Temporary_buffer<_ForwardIterator, _ValueType> __buf(__first, __last);
+      _Temporary_buffer<_ForwardIterator, _ValueType>
+	__buf(__first, std::distance(__first, __last));
       return
 	std::__stable_partition_adaptive(__first, __last, __pred,
 					 _DistanceType(__buf.requested_size()),
@@ -2534,7 +2535,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       const _DistanceType __len2 = std::distance(__middle, __last);
 
       typedef _Temporary_buffer<_BidirectionalIterator, _ValueType> _TmpBuf;
-      _TmpBuf __buf(__first, __last);
+      _TmpBuf __buf(__first, __len1 + __len2);
 
       if (__buf.begin() == 0)
 	std::__merge_without_buffer
@@ -4992,7 +4993,7 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
 	_DistanceType;
 
       typedef _Temporary_buffer<_RandomAccessIterator, _ValueType> _TmpBuf;
-      _TmpBuf __buf(__first, __last);
+      _TmpBuf __buf(__first, std::distance(__first, __last));
 
       if (__buf.begin() == 0)
 	std::__inplace_stable_sort(__first, __last, __comp);
diff --git a/libstdc++-v3/include/bits/stl_tempbuf.h b/libstdc++-v3/include/bits/stl_tempbuf.h
index 56c4ac5..159ee27 100644
--- a/libstdc++-v3/include/bits/stl_tempbuf.h
+++ b/libstdc++-v3/include/bits/stl_tempbuf.h
@@ -158,9 +158,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
       /**
        * Constructs a temporary buffer of a size somewhere between
-       * zero and the size of the given range.
+       * zero and the given length.
        */
-      _Temporary_buffer(_ForwardIterator __first, _ForwardIterator __last);
+      _Temporary_buffer(_ForwardIterator __seed, size_type __original_len);
 
       ~_Temporary_buffer()
       {
@@ -241,9 +241,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   template<typename _ForwardIterator, typename _Tp>
     _Temporary_buffer<_ForwardIterator, _Tp>::
-    _Temporary_buffer(_ForwardIterator __first, _ForwardIterator __last)
-    : _M_original_len(std::distance(__first, __last)),
-      _M_len(0), _M_buffer(0)
+    _Temporary_buffer(_ForwardIterator __seed, size_type __original_len)
+    : _M_original_len(__original_len), _M_len(0), _M_buffer(0)
     {
       __try
 	{
@@ -253,7 +252,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	  _M_len = __p.second;
 	  if (_M_buffer)
 	    std::__uninitialized_construct_buf(_M_buffer, _M_buffer + _M_len,
-					       __first);
+					       __seed);
 	}
       __catch(...)
 	{
@@ -268,4 +267,3 @@ _GLIBCXX_END_NAMESPACE_VERSION
 } // namespace
 
 #endif /* _STL_TEMPBUF_H */
-
diff --git a/libstdc++-v3/include/ext/memory b/libstdc++-v3/include/ext/memory
index c5d526e..fcc4948 100644
--- a/libstdc++-v3/include/ext/memory
+++ b/libstdc++-v3/include/ext/memory
@@ -184,7 +184,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     {
       /// Requests storage large enough to hold a copy of [first,last).
       temporary_buffer(_ForwardIterator __first, _ForwardIterator __last)
-      : _Temporary_buffer<_ForwardIterator, _Tp>(__first, __last) { }
+      : _Temporary_buffer<_ForwardIterator, _Tp>(__first,
+						 std::distance(__first, __last))
+      { }
       
       /// Destroys objects and frees storage.
       ~temporary_buffer() { }