gistfile1.txt

// mcs -unsafe -debug- Spaces.cs; time mono -O=all  ./Spaces.exe

using System;
using System.Threading.Tasks;

public class Spaces {
    static unsafe string GetTest(int len) {
        var s = new string(' ', len);
        fixed (char* pS = s) {
            for (int i = 0; i < len; ++i) {
                pS[i] = (char)('0' + (i % 10));
            }
        }
        return s;
    }

    public static void Main(string[] args) {
        var s = GetTest(1000000);
        string r;
        int totalLen = 0;
        for (int i = 0; i < 10; ++i) {
            r = InjectSpaces(s);
            totalLen += r.Length;
        }
        Console.WriteLine("Total length: {0}", totalLen);
        //Console.WriteLine("'{0}' -> '{1}'", s, r);
    }

    static unsafe string InjectSpaces(string s) {
        fixed (char* pS = s) {
            var pLength = (int*)pS - 1;
            var length = *pLength & 0x3fffffff;
            var result = new string(' ', 2*length - 1);
            fixed (char* pResult = result) {
                for (int i = 0; i < length; ++i) {
                    pResult[2*i] = pS[i];
                }
            }
            return result;
        }
    }
    
    static string InjectSpaces2(string s) {
        var ra = new char[s.Length * 2 - 1];
        ra[0] = s[0];
        Parallel.For(1, s.Length, (i) => {
            ra[2*i - 1] = ' ';
            ra[2*i] = s[i];
        });

        return new string (ra);
    }
    
    static string InjectSpaces3(string s) {
        var ra = new char[s.Length * 2 - 1];
        ra[0] = s[0];
        for (int i = 1; i < s.Length; ++i) {
            ra[2*i - 1] = ' ';
            ra[2*i] = s[i];
        }

        return new string (ra);
    }}
#include <iostream>
#include <string>

using namespace std;

static string InjectSpaces(const string& s) {
    string result(2*s.length() - 1, ' ');
    char* pResult = (char*)result.data();
    const char* pS = s.data();
    const auto length = s.length();
    for (auto i = 0; i < length; ++i) {
        pResult[2*i] = pS[i];
    }
    return result;
}

int main() {
    string s(1000000, ' ');
    char* pS = (char*)s.data();
    for (size_t i = 0; i < s.length(); ++i) {
        s[i] = '0' + (i % 10);
    }
    string result;
    int totalLength = 0;
    for (size_t i = 0; i < 10; ++i) {
        result = InjectSpaces(s);
        totalLength += result.length();
    }
    cout << totalLength << endl;

    return 0;
}