rom/timer/subtime.c

   1 /*
   2     Copyright © 1995-2007, The AROS Development Team. All rights reserved.
   3     $Id$
   4
   5     Desc: SubTime - subtract two timevals from each other.
   6     Lang: english
   7 */
   8 #include "timer_intern.h"
   9
  10 /*****************************************************************************
  11
  12     NAME */
  13 #include <devices/timer.h>
  14 #include <proto/timer.h>
  15
  16         AROS_LH2(void, SubTime,
  17
  18 /*  SYNOPSIS */
  19         AROS_LHA(struct timeval *, dest, A0),
  20         AROS_LHA(struct timeval *, src, A1),
  21
  22 /*  LOCATION */
  23         struct Device *, TimerBase, 8, Timer)
  24
  25 /*  FUNCTION
  26         SubTime() will subtract the src timeval from the destination
  27         timeval, ie "dest - src --> dest".
  28
  29     INPUTS
  30         dest    -   Destination timeval
  31         src     -   Source timeval
  32
  33     RESULT
  34         The timeval dest will contain the sum (dest - src).
  35
  36     NOTES
  37         This function is safe to call from interrupts.
  38
  39     EXAMPLE
  40
  41     BUGS
  42         May not preserve registers.
  43
  44     SEE ALSO
  45         AddTime(), CmpTime()
  46
  47     INTERNALS
  48
  49     HISTORY
  50         18-02-1997  iaint   Implemented.
  51
  52 *****************************************************************************/
  53 {
  54     AROS_LIBFUNC_INIT
  55
  56     /* Normalize the terms */
  57     while(src->tv_micro > 999999)
  58     {
  59         src->tv_secs++;
  60         src->tv_micro -= 1000000;
  61     }
  62     while(dest->tv_micro > 999999)
  63     {
  64         dest->tv_secs++;
  65         dest->tv_micro -= 1000000;
  66     }
  67
  68     /* Check if wrap around will happen, when subtracting src->tv_micro
  69        from dest->tv_micro. If yes, then normalize, by adding 1 sec to
  70        micros and subtracting 1 sec from secs. Note: this check must be
  71        done here, ie. before subtracting src timeval from dest timeval! */
  72
  73     if(dest->tv_micro < src->tv_micro)
  74     {
  75         dest->tv_micro += 1000000;
  76         dest->tv_secs--;
  77     }
  78
  79     dest->tv_micro -= src->tv_micro;
  80     dest->tv_secs -= src->tv_secs;
  81
  82     AROS_LIBFUNC_EXIT
  83
  84 } /* SubTime */