panthema / 2007 (page 2 of 1 2)
Thumbnail der fertig aufgestellten Duetta

Lautsprecher-Odyssee und Duetta Selbstbau

Posted on 2007-04-18 19:00 by Timo Bingmann at Permlink with 23 Comments. Tags: hifi selbstbau

Zusammenfassung

In diesem Blog-Eintrag beschreibe ich meine drei-monatige, intensive Suche nach neuen Lautsprechern. Der Eintrag enthält viele persönliche Meinungen und soll insbesondere zu der Zeit angestellte Überlegungen und Vermutungen erfassen. Dieser Bericht soll sein, was ich in damals vergeblich im Internet gesucht habe: eine detaillierte Entwicklung von völlig unerfahrenen Musikhörer zum Boxen-Selbstbauer. Der ganze Bericht ist natürlich subjektiv, manch Suchender wird völlig anderer Meinung sein.

Die Suche startet im letzten Dezember bei den einschlägigen Elektronikmärkten. Mit den bekannten Test-Magazinen bewaffnet, hätte ich dort um Haaresbreite ein Paar Lautsprecher gekauft. Durch Zufall kamen wir dann zu Orbid-Sound und durften dort begeistert alles probe hören und sogar zwei Paar Lautsprecher ausleihen. Am Ende landete ich jedoch beim HiFi-Selbstbau. Nach langem Vergleich der verschiedenen im Internet verfügbaren Bausätze entschied ich mich zu Udo Wohlgemuth nach Bochum zu fahren und dort zwei Duetta-Bausätze zu kaufen.

Die zehntägige Bastelarbeit an dem Paar Duettas hat mir sehr viel Spaß gemacht. Hier werden die einzelnen Schritte nur kurz beschrieben aber durch viele Photos illustriert. Besonderes Augenmerk legte ich auf die Schwierigkeiten, welche ich damals als totaler Selbstbau-Neuling überwinden musste. Der Blog-Eintrag endet mit einer differenzierten Beschreibung des Klangs meiner Duettas.

This blog entry continues on the next page ...

Thumbnail of the current HMTG Webpage

HMTG Web Page Redesign

Posted on 2007-04-14 20:24 by Timo Bingmann at Permlink with 0 Comments. Tags: webdesign hartmetall

Finished redesigning the web site and e-catalog of the Hartmetall-Gesellschaft. This is actually the fifth version of the homepage. It is now based on Template::Toolkit technology with the old PostgreSQL database back-end. The style was adapted to todays modern web designs.

On this occasion I have collected and organized versions of older home pages. They show a stream of development which the page has taken:

This blog entry continues on the next page ...

C++ Code Snippet - Compressing STL Strings with zlib

Posted on 2007-03-28 18:23 by Timo Bingmann at Permlink with 11 Comments. Tags: c++ code-snippet frontpage

The zlib library can be found on virtually every computer. It is THE general-purpose lossless patent-free compression library.

This small C++ code snippet features a pair of functions which use this ubiquitous library to compress ordinary STL strings. There are many uses for this code snippet, like compressing string data stored in a database or binary data transfered over a network. Keep in mind that the compressed string data is binary, so the string's c_str() representation must be avoided.

To compile the following small program use "gcc testzlib.cc -o testzlib -lz" where testzlib.cc is the code.

// Copyright 2007 Timo Bingmann <tb@panthema.net>
// Distributed under the Boost Software License, Version 1.0.
// (See http://www.boost.org/LICENSE_1_0.txt)

#include <string>
#include <stdexcept>
#include <iostream>
#include <iomanip>
#include <sstream>

#include <zlib.h>

/** Compress a STL string using zlib with given compression level and return
  * the binary data. */
std::string compress_string(const std::string& str,
                            int compressionlevel = Z_BEST_COMPRESSION)
{
    z_stream zs;                        // z_stream is zlib's control structure
    memset(&zs, 0, sizeof(zs));

    if (deflateInit(&zs, compressionlevel) != Z_OK)
        throw(std::runtime_error("deflateInit failed while compressing."));

    zs.next_in = (Bytef*)str.data();
    zs.avail_in = str.size();           // set the z_stream's input

    int ret;
    char outbuffer[32768];
    std::string outstring;

    // retrieve the compressed bytes blockwise
    do {
        zs.next_out = reinterpret_cast<Bytef*>(outbuffer);
        zs.avail_out = sizeof(outbuffer);

        ret = deflate(&zs, Z_FINISH);

        if (outstring.size() < zs.total_out) {
            // append the block to the output string
            outstring.append(outbuffer,
                             zs.total_out - outstring.size());
        }
    } while (ret == Z_OK);

    deflateEnd(&zs);

    if (ret != Z_STREAM_END) {          // an error occurred that was not EOF
        std::ostringstream oss;
        oss << "Exception during zlib compression: (" << ret << ") " << zs.msg;
        throw(std::runtime_error(oss.str()));
    }

    return outstring;
}

/** Decompress an STL string using zlib and return the original data. */
std::string decompress_string(const std::string& str)
{
    z_stream zs;                        // z_stream is zlib's control structure
    memset(&zs, 0, sizeof(zs));

    if (inflateInit(&zs) != Z_OK)
        throw(std::runtime_error("inflateInit failed while decompressing."));

    zs.next_in = (Bytef*)str.data();
    zs.avail_in = str.size();

    int ret;
    char outbuffer[32768];
    std::string outstring;

    // get the decompressed bytes blockwise using repeated calls to inflate
    do {
        zs.next_out = reinterpret_cast<Bytef*>(outbuffer);
        zs.avail_out = sizeof(outbuffer);

        ret = inflate(&zs, 0);

        if (outstring.size() < zs.total_out) {
            outstring.append(outbuffer,
                             zs.total_out - outstring.size());
        }

    } while (ret == Z_OK);

    inflateEnd(&zs);

    if (ret != Z_STREAM_END) {          // an error occurred that was not EOF
        std::ostringstream oss;
        oss << "Exception during zlib decompression: (" << ret << ") "
            << zs.msg;
        throw(std::runtime_error(oss.str()));
    }

    return outstring;
}

/** Small dumb tool (de)compressing cin to cout. It holds all input in memory,
  * so don't use it for huge files. */
int main(int argc, char* argv[])
{
    std::string allinput;

    while (std::cin.good())     // read all input from cin
    {
        char inbuffer[32768];
        std::cin.read(inbuffer, sizeof(inbuffer));
        allinput.append(inbuffer, std::cin.gcount());
    }

    if (argc >= 2 && strcmp(argv[1], "-d") == 0)
    {
        std::string cstr = decompress_string( allinput );

        std::cerr << "Inflated data: "
                  << allinput.size() << " -> " << cstr.size()
                  << " (" << std::setprecision(1) << std::fixed
                  << ( ((float)cstr.size() / (float)allinput.size() - 1.0) * 100.0 )
                  << "% increase).\n";

        std::cout << cstr;
    }
    else
    {
        std::string cstr = compress_string( allinput );

        std::cerr << "Deflated data: "
                  << allinput.size() << " -> " << cstr.size()
                  << " (" << std::setprecision(1) << std::fixed
                  << ( (1.0 - (float)cstr.size() / (float)allinput.size()) * 100.0)
                  << "% saved).\n";

        std::cout << cstr;
    }
}

C++ Code Snippet - Using the Boost.Regex Library

Posted on 2007-03-14 14:43 by Timo Bingmann at Permlink with 0 Comments. Tags: c++ code-snippet

The Boost library is a collection of very useful C++ (template) libraries. However it's documentation is very complex and using the library straight-forward usually results in g++ scrolling endless pages of template instantiation errors.

This code snippet shows by example how to use the Boost.Regex library. It compiles and executes regular expressions on strings. Some test I ran showed that it is not as fast as pcre, however Boost.Regex it is easier and more elegant to use in C++ programs. The program must be linked with -lboost_regex.

#include <iostream>
#include <stdlib.h>
#include <boost/regex.hpp>
#include <boost/lexical_cast.hpp>

int main()
{
    // This regex is compiled at start-up and matches YYYY-MM-DD dates. If it
    // contains a syntax error, the program aborts at start-up with an
    // exception.
    static const boost::regex
        date_regex("(199[0-9]|200[0-9])-([1-9]|0[1-9]|1[012])-([1-9]|[0-2][1-9]|3[01])");

    // First example: char* c-style input strings use boost::cmatch results.
    {
        const char *input_cstr = "2007-03-14";
        boost::cmatch char_matches;

        if (boost::regex_match(input_cstr, char_matches, date_regex))
        {
            // Convert the parsed number using boost's lexical_cast library
            int year = boost::lexical_cast<int>( char_matches[1] );
            // Or use the old way: get the std::string object, then it's char*
            int month = atoi( char_matches[2].str().c_str() );

            std::cout << "First example:"
                      << " year " << year
                      << " month " << month
                      << " day " << char_matches[3] << "\n";
        } 
        else
        {
            std::cout << "First example should have matched the regex.\n";
        }
    }

    // Second example: STL strings use boost::smatch results.
    {
        std::string input_stlstr = "2007-03-34";
        boost::smatch str_matches;

        if (boost::regex_match(input_stlstr, str_matches, date_regex))
        {
            std::cout << "Second example shouldn't have matched the regex.\n";
        }
        else
        {
            std::cout << "Second example didn't match the regex. This was intended.\n";
        }
    }

    // Third example: Temporary regex object and no capture results needed.
    {
        if (boost::regex_match("2007", boost::regex("(199[0-9]|200[0-9])")))
        {
            std::cout << "Third example matched the temporary regex object.\n";
        }
        else
        {
            std::cout << "Third example should have matched the regex.\n";
        }
    }

    // Fourth example: regex_match matches the whole string while regex_search
    // matches substrings just like perl.
    {
        std::string input = "Today is 2007-03-14, how are you?";

        if (boost::regex_match(input, date_regex))
        {
            std::cout << "Fourth example (regex_match) shouldn't match.\n";
        }
        else
        {
            std::cout << "As expected, the fourth example (regex_match) didn't match.\n";
        }

        if (boost::regex_search(input, date_regex))
        {
            std::cout << "While the fourth example using regex_search did matched.\n";
        }
        else
        {
            std::cout << "Fourth example using regex_search should have matched the regex.\n";
        }
    }
}

C++ Code Snippet - Making a Custom Class ostream Outputable

Posted on 2007-03-01 14:47 by Timo Bingmann at Permlink with 1 Comments. Tags: c++ code-snippet

How to get a custom class to work with std::cout << obj; ? I for my part always forget the exact prototype of the required operator<<. Here is an minimal working example to copy code from:

#include <iostream>

struct myclass
{
    int a, b;

    myclass(int _a, int _b)
        : a(_a), b(_b)
    { }
};

// make myclass ostream outputtable
std::ostream& operator<< (std::ostream &stream, const myclass &obj)
{
    return stream << "(" << obj.a << "," << obj.b << ")";
}

int main()
{
    myclass obj(42, 46);

    std::cout << obj << std::endl;
}

Thumbnail of first slide of presentation

NetFundamentals Seminar - Presentation Today

Posted on 2007-01-29 19:00 by Timo Bingmann at Permlink with 0 Comments. Tags: netfundamentals university talk

Following up on the technical report, today Dimitar and myself gave a 70min presentation on Robert Gallager's Minimum Delay Routing Algorithm Using Distributed Computation. It finished my work for the NetFundamentals seminar, which was organized by Decentralized Systems and Network Services Research Group at the Institute of Telematics. The seminar was very profound and extensively dug into the mathematics of six fundamental networking papers. Besides that it was great fun and opened some new horizons.

Our presentation can be downloaded as PDF (553 KB), with two slides per page or even with four per page.

Furthermore our listeners were given an equation sheet (139 KB) to aid them in following the many formulas.


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