http parsing speed

#include <ctime>
#include <iostream>
#include <iomanip>
#include <map>
#include <string>
#include <string.h>

std::map<std::string, std::string> http_request;

void parse_header_old( const char *, std::size_t );
void parse_header_new( const char *, const char * );

int main()
{
    const char msg[]= "GET / HTTP/1.1\r\n"
                      "Host: 192.241.213.46:6880\r\n"
                      "Upgrade-Insecure-Requests: 1\r\n"
                      "Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8\r\n"
                      "User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_3) AppleWebKit/602.4.8 (KHTML, like Gecko) Version/10.0.3 Safari/602.4.8\r\n"
                      "Accept-Language: en-us\r\n"
                      "Accept-Encoding: gzip, deflate\r\n"
                      "Connection: keep-alive\r\n\r\n";

    clock_t begin;

    begin = clock();

    parse_header_old( msg, sizeof( msg ) );

    printf("old: %f\n", (double)( clock() - begin ) / CLOCKS_PER_SEC);


    begin = clock();

    parse_header_new( msg, &msg[ sizeof( msg ) - 1 ] );

    printf("new: %f\n", (double)( clock() - begin ) / CLOCKS_PER_SEC);

}

/*
 * Before
 */
void parse_header_old( const char *msg, std::size_t len )
{
    char *head = (char *) msg;
    char *mid;
    char *tail = head;

    if( len == 0 )
    {
        return;
    }

    // Find request type
    while( *head++ != ' ');
    http_request[ "Type" ] = std::string( ( char * ) msg ).substr( 0 , ( head - 1) - tail );

    // Find path
    tail = head;
    while( *head++ != ' ');
    http_request[ "Path" ] = std::string( ( char * ) msg ).substr( tail - ( char *)msg , ( head - 1) - tail );

    // Find HTTP version
    tail = head;
    while( *head++ != '\r');
    http_request[ "Version" ] = std::string( ( char * ) msg ).substr( tail - ( char *)msg , ( head - 1) - tail );

    // Map all headers from a key to a value
    while( true )
    {
        tail = head + 1;
        while( *head++ != '\r' );
        mid = strstr( tail, ":" );

        // Look for the failed strstr
        if( tail > mid )
            break;

        http_request[ std::string( ( char * ) msg ).substr( tail - ( char *)msg , ( mid ) - tail  ) ] = std::string( ( char * ) msg ).substr( mid + 2 - ( char *) msg , ( head - 3 ) - mid );
    }
}

void parse_header_new( const char *msg, const char *msg_end )
{
    const char *head = msg;
    const char *tail = msg;

    // Find request type
    while (tail != msg_end && *tail != ' ') ++tail;
    http_request["Type"] = std::string(head, tail);

    // Find path
    while (tail != msg_end && *tail == ' ') ++tail;
    head = tail;
    while (tail != msg_end && *tail != ' ') ++tail;
    http_request["Path"] = std::string(head, tail);

    // Find HTTP version
    while (tail != msg_end && *tail == ' ') ++tail;
    head = tail;
    while (tail != msg_end && *tail != '\r') ++tail;
    http_request["Version"] = std::string(head, tail);
    if (tail != msg_end) ++tail;  // skip '\r'
    if (tail != msg_end) ++tail;  // skip '\n'

    // Map all headers from a key to a value
    head = tail;
    while ( head + 2 != msg_end )
    {
        while (tail != msg_end && *tail != '\r') ++tail;
        const char *colon = ( char * )memchr(head, ':', tail - head);
        if (colon == NULL) {
            std::cout << "colon not found." << std::endl;
            return;//break;
        }
        const char *value = colon+1;
        while (value != tail && *value == ' ') ++value;
        http_request[ std::string(head, colon) ] = std::string(value, tail);
        head = tail+2;
        if (tail != msg_end) ++tail;  // skip '\r'
        if (tail != msg_end) ++tail;  // skip '\n'
    }
}