[Bug libstdc++/13341] New: ctype<wchar_t>::do_narrow(wchar_t, char) is slow

["paolo at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

Consider the following code: it shows that by building at construction time
a simple table for all the wchar_t from 0 to 128, the speed of narrow can be
increased by a factor of 10 in the common case.
Similarly for the array version and for widen (both single char and array).

///////////////////////////

#include <cwchar>
#include <locale>

struct CtypeS: std::ctype<wchar_t>
{
 char
 do_narrow(wchar_t __wc, char __dfault) const
 {
   int __c = wctob(__wc);
   return (__c == EOF ? __dfault : static_cast<char>(__c));
 }
};

struct CtypeF: std::ctype<wchar_t>
{
 int cached[128];

 char
 do_narrow(wchar_t __wc, char __dfault) const
 {
   int __c;
   if (__wc < 128)
     __c = cached[__wc];
   else
     __c = wctob(__wc);

   return (__c == EOF ? __dfault : static_cast<char>(__c));
 }
};

int main()
{
 using namespace std;

 //locale loc = locale(locale::classic(), new CtypeF);
 locale loc = locale(locale::classic(), new CtypeS);

 const ctype<wchar_t>& ct = use_facet<ctype<wchar_t> >(loc);

 for (long i = 0; i < 100000000; ++i)
   ct.narrow(i % 128, '*');
}

//////////////////////////

-- 
           Summary: ctype<wchar_t>::do_narrow(wchar_t, char) is slow
           Product: gcc
           Version: 3.4
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: libstdc++
        AssignedTo: paolo at gcc dot gnu dot org
        ReportedBy: paolo at gcc dot gnu dot org
                CC: gcc-bugs at gcc dot gnu dot org
  GCC host triplet: Any
GCC target triplet: Any


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13341