# Stefan Teleman <[email protected]>

# 1. Clearer cast not relying on array index -1.

# 2. Optimization based on initial std::string size and capacity.

# Internal patch. Not submitted upstream yet.

--- libstdc++-v3/include/bits/basic_string.h	2015-05-28 12:27:46.000000000 -0400

+++ libstdc++-v3/include/bits/basic_string.h	2015-09-14 01:16:05.666069507 -0400

@@ -131,6 +131,15 @@

       typedef std::reverse_iterator<iterator>		    reverse_iterator;

     private:

+      // Use empty-base optimization: http://www.cantrip.org/emptyopt.html

+      struct _Alloc_hider : _Alloc

+      {

+	_Alloc_hider(_CharT* __dat, const _Alloc& __a) _GLIBCXX_NOEXCEPT

+	: _Alloc(__a), _M_p(__dat) { }

+

+	_CharT* _M_p; // The actual data.

+      };

+

       // _Rep: string representation

       //   Invariants:

       //   1. String really contains _M_length + 1 characters: due to 21.3.4

@@ -268,15 +277,6 @@

 	_M_clone(const _Alloc&, size_type __res = 0);

       };

-      // Use empty-base optimization: http://www.cantrip.org/emptyopt.html

-      struct _Alloc_hider : _Alloc

-      {

-	_Alloc_hider(_CharT* __dat, const _Alloc& __a) _GLIBCXX_NOEXCEPT

-	: _Alloc(__a), _M_p(__dat) { }

-

-	_CharT* _M_p; // The actual data.

-      };

-

     public:

       // Data Members (public):

       // NB: This is an unsigned type, and thus represents the maximum

@@ -298,7 +298,10 @@

       _Rep*

       _M_rep() const _GLIBCXX_NOEXCEPT

-      { return &((reinterpret_cast<_Rep*> (_M_data()))[-1]); }

+      {

+        _Rep* __r = static_cast<_Rep*>(reinterpret_cast<void*>(_M_data()));

+        return --__r;

+      }

       // For the internal use we have functions similar to `begin'/`end'

       // but they do not call _M_leak.

--- libstdc++-v3/include/bits/basic_string.tcc	2014-01-02 17:30:10.000000000 -0500

+++ libstdc++-v3/include/bits/basic_string.tcc	2015-09-14 01:16:09.408163359 -0400

@@ -575,7 +575,8 @@

       // malloc implementations that allocate memory blocks rounded up

       // to a size which is a power of 2).

       const size_type __pagesize = 4096;

-      const size_type __malloc_header_size = 4 * sizeof(void*);

+      const size_type __min_capacity = 32;

+      const size_type __malloc_header_size = 8 * sizeof(void*);

       // The below implements an exponential growth policy, necessary to

       // meet amortized linear time requirements of the library: see

@@ -586,6 +587,9 @@

       if (__capacity > __old_capacity && __capacity < 2 * __old_capacity)

 	__capacity = 2 * __old_capacity;

+      if (__capacity < __min_capacity)

+        __capacity = __min_capacity;

+

       // NB: Need an array of char_type[__capacity], plus a terminating

       // null char_type() element, plus enough for the _Rep data structure.

       // Whew. Seemingly so needy, yet so elemental.