contrib/ntp/libntp/calleapwhen.c

   1 /*
   2  * calleapwhen - determine the number of seconds to the next possible
   3  *               leap occurance.
   4  */
   5 #include <sys/types.h>
   6
   7 #include "ntp_types.h"
   8 #include "ntp_calendar.h"
   9 #include "ntp_stdlib.h"
  10
  11 /*
  12  * calleaptab - leaps occur at the end of December and June
  13  */
  14 long calleaptab[10] = {
  15         -(JAN+FEBLEAP)*SECSPERDAY,      /* leap previous to cycle */
  16         (MAR+APR+MAY+JUN)*SECSPERDAY,   /* end of June */
  17         (MAR+APR+MAY+JUN+JUL+AUG+SEP+OCT+NOV+DEC)*SECSPERDAY, /* end of Dec */
  18         (MAR+APR+MAY+JUN)*SECSPERDAY + SECSPERYEAR,
  19         (MAR+APR+MAY+JUN+JUL+AUG+SEP+OCT+NOV+DEC)*SECSPERDAY + SECSPERYEAR,
  20         (MAR+APR+MAY+JUN)*SECSPERDAY + 2*SECSPERYEAR,
  21         (MAR+APR+MAY+JUN+JUL+AUG+SEP+OCT+NOV+DEC)*SECSPERDAY + 2*SECSPERYEAR,
  22         (MAR+APR+MAY+JUN)*SECSPERDAY + 3*SECSPERYEAR,
  23         (MAR+APR+MAY+JUN+JUL+AUG+SEP+OCT+NOV+DEC)*SECSPERDAY + 3*SECSPERYEAR,
  24         (MAR+APR+MAY+JUN+JUL+AUG+SEP+OCT+NOV+DEC+JAN+FEBLEAP+MAR+APR+MAY+JUN)
  25         *SECSPERDAY + 3*SECSPERYEAR,    /* next after current cycle */
  26 };
  27
  28 u_long
  29 calleapwhen(
  30         u_long ntpdate
  31         )
  32 {
  33         register u_long dateincycle;
  34         register int i;
  35
  36         /*
  37          * Find the offset from the start of the cycle
  38          */
  39         dateincycle = ntpdate;
  40         if (dateincycle >= MAR1988)
  41             dateincycle -= MAR1988;
  42         else
  43             dateincycle -= MAR1900;
  44
  45         while (dateincycle >= SECSPERCYCLE)
  46             dateincycle -= SECSPERCYCLE;
  47
  48         /*
  49          * Find where we are with respect to the leap events.
  50          */
  51         for (i = 1; i < 9; i++)
  52             if (dateincycle < (u_long)calleaptab[i])
  53                 break;
  54
  55         /*
  56          * i points at the next leap.  Compute the last and the next.
  57          */
  58         return (u_long)(calleaptab[i] - (long)dateincycle);
  59 }