[STDCXX-493] std::string::append() slow - ASF JIRA

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This is a similar problem to ~~STDCXX-492~~: all overloads of string::append() are slower than the same overloads in gcc:

$ let n=0; while [ $n -lt 3 ]; do time LD_LIBRARY_PATH=../lib ./append-stdcxx-4.1.3 500000000 $n; let n=`expr $n + 1`; done

real 0m11.221s
user 0m9.941s
sys 0m1.104s

real 0m13.065s
user 0m11.661s
sys 0m1.236s

real 0m7.837s
user 0m6.660s
sys 0m1.160s

$ let n=0; while [ $n -lt 3 ]; do time ./append-gcc-4.1.2 500000000 $n; let n=`expr $n + 1`; done

real 0m4.865s
user 0m4.172s
sys 0m0.692s

real 0m7.617s
user 0m6.920s
sys 0m0.696s

real 0m5.787s
user 0m5.068s
sys 0m0.720s

The program I used to do the comaprison is below:

#include <cassert>
#include <cstdlib>
#include <string>

int main (int argc, char *argv[])
{
const int N = argc < 2 ? 1 : std::atoi (argv [1]);
const int op = argc < 3 ? 0 : std::atoi (argv [2]);

std::string str;

const std::string x ("X");

if (op == 0)

{ for (int i = 0; i < N; ++i) str.append (1, 'x'); }

else if (op == 1)

{ for (int i = 0; i < N; ++i) str.append ("x"); }

else

{ for (int i = 0; i < N; ++i) str.append (x); }

assert (str.size () == std::size_t (N));
}