Farid Zaripov wrote:
-----Original Message-----
From: Martin Sebor [mailto:[EMAIL PROTECTED] On Behalf Of Martin Sebor
Sent: Tuesday, July 24, 2007 7:40 AM
To: stdcxx-dev@incubator.apache.org
Subject: Re: [PATCH] for STDCXX-491 - string::push_back() slow
mark.g.brown wrote:
Hi all,
The attached simple patch speeds up push_back() nearly six times
relative to stdcxx 4.1.3 and makes it more than twice faster that
gcc's.
Let me test your patch for regressions and if it passes I'll
commit it tomorrow.
I see the difference between the old push_back() behavior and after
this patch.
The append (size_type (1), __c); also appends terminating NULL character
(string.cc, line 472). Below is the corrections to the patch:
Ah, yes, good catch!
On the subject of the terminating NUL, I wonder it would simplify
(and speed up) the implementation if we appended the terminating
NUL in c_str() instead in every modifying member function. We'd
still need to allocate enough memory for it because c_str() isn't
allowed to invalidate iterators, pointers, and references into
the object but we might be able to save ourselves a few CPU
cycles if we set data()[size()] to charT() only in c_str().
Hmmm, something to think about...
Martin
template <class _CharT, class _Traits , class _Allocator> inline
void basic_string<_CharT, _Traits, _Allocator>::
+push_back (value_type __c)
+{
+ const size_type __size = size () + 1;
+
+ if ( capacity () < __size
+ || size_type (1) < size_type (_C_pref ()->_C_get_ref ()))
+ append (1, __c);
+ else {
+ traits_type::assign (_C_data [size ()], __c);
// append the terminating NUL character
traits_type::assign (_C_data [__size], value_type ());
+ _C_pref ()->_C_size._C_size = __size;
+ }
+}
Farid.
