Ada.Real_Time alternative

Ada.Real_Time alternative

[W. Wesley Groleau (Wes)]

/*-------------------------------------------------------------------------
 *-------------------------------------------------------------------------
 * C : Ada_Real_Time_Support.c
 *-------------------------------------------------------------------------
 *-------------------------------------------------------------------------
 *---------------------------CONTROL INFORMATION---------------------------
 *                      Hughes Defense Communications
 *                          Fort Wayne, Indiana
 *
 * Project name:          AFATDS
 * Contract Number:       DAAB07-90-C-E708
 * CSCI:                  Reuse
 * CSC:                   Ada 95 Emulation
 * Unit:                  Ada.Real_Time
 *
 * Control Number:
 * Creation Date:         13 Dec 1996
 * Designer:              Wes Groleau
 * Programmer:            Wes Groleau
 *
 * Language:              C
 *
 * Host Environment:      HP UX 9.x on PA RISC
 *                        HP UX 9.x on 680x0
 *                        Solaris on Sparc
 *                        SCO Unix on Pentium
 *
 * Host Translator:       default 'cc' from O.S. vendor
 *                        gcc 2.4.5 or 2.7.2 (depending on machine)
 *
 * Change History:
 *      Revision  Date       Author       Description of Change
 *
 * Description: This file provides a way to measure elapsed time
 *              that is NOT affected by any priviliged process
 *              calling date(1), settimeofday(2), stime(2), or
 *              any other method for setting "wall" clock time.
 *              This code will work with no changes on all the
 *              listed systems.  By using the tick value to
 *              interpret the output of the clock, the calling
 *              code can be made portable as well.
 *              CLK_TCK is 50 on HP UX/680x0; 100 on the others.
 *              Maximum error in seconds is 1/CLK_TCK.
 *              With CLK_TCK 100, range is over 248.5 days.
 *              With CLK_TCK  50, range is twice that.
 *              Calling code can extend the range by detecting
 *              by detecting wrap-around and applying a correction.
 *
 *              OTHER DETAILS HAVE BEEN PROVIDED IN A MESSAGE TO
 *              THE chat@gnat.com MAILING LIST AND TO comp.lang.ada
 *              PLEASE READ THAT MESSAGE FOR MORE DETAILS.
*/

#include <errno.h>
#include <time.h>
#include <sys/times.h>

/* documentation is the man page for times(2)     */

long Ada_Real_Time_Tick()
{
   return CLK_TCK;
}


long Ada_Real_Time_Clock()
{
    struct  tms  Dummy;

    return times(&Dummy);
}


main()
/* this is just the test driver.  test commands:
 *      a.out; sleep 20; a.out
 * do twice--second time, change system "wall" clock during sleep.
 * verify that difference between "seconds" is reasonably close
 * to elapsed time on first run, and is not affected by time change
 * on second run.
 * repeat with much longer sleep to verify that imprecision
 * is due only to overhead of other commands, i.e., amount of
 * error is nearly constant, not affected by length of delay.
 * also compare 'uptime' with 'seconds' - should match
*/
{
    printf ("RTC:     %dl\n",    Ada_Real_Time_Clock() );
    printf ("errno:   %d\n",     errno                 ); /* just checking :-)
 */
    printf ("Tick:    %dl\n",    Ada_Real_Time_Tick()  );
    printf ("Seconds: %20.6f\n", (float) Ada_Real_Time_Clock()  /
                                 (float) Ada_Real_Time_Tick()     );
}

/*   Test Results
 *
 *   Platform         Compiler   sleep         measured time
 *                                          normal      w/ clock change
 *
 *   680x0            cc           20       20.560000
 *   680x0            cc         3600     3600.860000
 *   680x0            gcc          20       20.437000
 *   RISC             cc           20       20.030000     20.030000
 *   RISC             cc           20                     20.890000
 *   RISC             cc         1634*    1594.470000*
 *   RISC             gcc          20       20.030273     20.029296
 *   RISC             gcc          20                     20.040273
 *   Sparc            gcc          20       20.000000
 *   Sparc            gcc         100      100.250000
 *   Pentium          cc           20       20.260000
 *
 *   * the starred measurements were obtained by 'a.out; date'
 *     executed twice--'sleep' was not used, and the "wall" clock
 *     was not changed.
 *
 * "seconds" is time since startup?
 * 680x0 (pseserv3)              very close/9 days
 * RISC                          uptime 5:12 (h:mm); no measurable error
 * Sparc                         lost ~3 min./44 days
 * Pentium / SCO                 NO - up 5 days 3:37, times gave about 6 days
*/