Added a comment from Juergen Perlinger in ntp_date.c to make the code clearer.

bk: 550af29e0iDzLwRNQeqyKhBJ3BJF8w

diff --git a/ChangeLog b/ChangeLog
index c35f9ca8b22f960f6598d6d7d1a97ddae64c537e..7404a0eb6326347063f06610fd271aad2684d08b 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,6 @@
 ---
 
+* Added a comment from Juergen Perlinger in ntp_date.c to make the code clearer.
 * Use predefined function types for parse driver functions
   used to set up function pointers.
   Account for changed prototype of parse_inp_fnc_t functions.

diff --git a/libntp/ntp_calendar.c b/libntp/ntp_calendar.c
index 94ca0e9ee154ba8f22e480146affa2bd992f3b65..ff91fcfc678d7a672b96a066d10a53de854feac3 100644 (file)
--- a/libntp/ntp_calendar.c
+++ b/libntp/ntp_calendar.c
@@ -29,7 +29,7 @@ ntpcal_set_timefunc(
        )
 {
        systime_func_ptr res;
-       
+
        res = systime_func;
        if (NULL == nfunc)
                nfunc = &time;
@@ -118,7 +118,7 @@ vint64_to_time(
 #endif
 
        return res;
-} 
+}
 
 /*
  *---------------------------------------------------------------------
@@ -170,7 +170,7 @@ ntpcal_get_build_date(
 #ifdef DEBUG
        static int        ignore  = 0;
 #endif
-       
+
        ZERO(*jd);
        jd->year     = 1970;
        jd->month    = 1;
@@ -255,7 +255,7 @@ static const uint16_t real_month_table[2][13] = {
  * in the proleptic Gregorian calendar. The begin of the Christian Era
  * (0001-01-01) is RD(1).
  *
- * 
+ *
  * Some notes on the implementation:
  *
  * Calendar algorithms thrive on the division operation, which is one of
@@ -351,7 +351,7 @@ ntpcal_periodic_extend(
        char     cpl = 0; /* modulo complement flag */
        char     neg = 0; /* sign change flag       */
 
-       /* make the cycle positive and adjust the flags */ 
+       /* make the cycle positive and adjust the flags */
        if (cycle < 0) {
                cycle = - cycle;
                neg ^= 1;
@@ -407,21 +407,21 @@ ntpcal_ntp_to_time(
 
 #ifdef HAVE_INT64
 
-       res.q_s = (pivot != NULL) 
+       res.q_s = (pivot != NULL)
                      ? *pivot
-                     : now();  
+                     : now();
        res.Q_s -= 0x80000000;          /* unshift of half range */
        ntp     -= (uint32_t)JAN_1970;  /* warp into UN*X domain */
        ntp     -= res.D_s.lo;          /* cycle difference      */
        res.Q_s += (uint64_t)ntp;       /* get expanded time     */
 
 #else /* no 64bit scalars */
-       
+
        time_t tmp;
-       
-       tmp = (pivot != NULL) 
+
+       tmp = (pivot != NULL)
                  ? *pivot
-                 : now();      
+                 : now();
        res = time_to_vint64(&tmp);
        M_SUB(res.D_s.hi, res.D_s.lo, 0, 0x80000000);
        ntp -= (uint32_t)JAN_1970;      /* warp into UN*X domain */
@@ -465,9 +465,9 @@ ntpcal_ntp_to_ntp(
        res.Q_s += (uint64_t)ntp;       /* get expanded time     */
 
 #else /* no 64bit scalars */
-       
+
        time_t tmp;
-       
+
        tmp = (pivot)
                  ? *pivot
                  : now();
@@ -492,7 +492,7 @@ ntpcal_ntp_to_ntp(
  */
 
 /*
- *------------------------------------------------------------------- 
+ *-------------------------------------------------------------------
  * Split a 64bit seconds value into elapsed days in 'res.hi' and
  * elapsed seconds since midnight in 'res.lo' using explicit floor
  * division. This function happily accepts negative time values as
@@ -532,7 +532,7 @@ ntpcal_daysplit(
        isneg = M_ISNEG(op.D_s.hi);
        if (isneg)
                M_NEG(op.D_s.hi, op.D_s.lo);
-               
+
        /* save remainder of DIV 128, shift for divide */
        r  = op.D_s.lo & 127; /* save remainder bits */
        op.D_s.lo = (op.D_s.lo >> 7) | (op.D_s.hi << 25);
@@ -572,16 +572,16 @@ ntpcal_daysplit(
                } else
                        q = ~q + 1;
        }
-       
+
        res.hi = q;
        res.lo = r;
 
-#endif 
+#endif
        return res;
 }
 
 /*
- *------------------------------------------------------------------- 
+ *-------------------------------------------------------------------
  * Split a 32bit seconds value into h/m/s and excessive days.  This
  * function happily accepts negative time values as timestamps before
  * midnight.
@@ -632,7 +632,7 @@ ntpcal_split_eradays(
 {
        ntpcal_split res;
        int32_t      n400, n100, n004, n001, yday; /* calendar year cycles */
-       
+
        /*
         * Split off calendar cycles, using floor division in the first
         * step. After that first step, simple division does it because
@@ -652,7 +652,7 @@ ntpcal_split_eradays(
        yday = yday % GREGORIAN_NORMAL_LEAP_CYCLE_DAYS;
        n001 = yday / DAYSPERYEAR;
        yday = yday % DAYSPERYEAR;
-       
+
        /*
         * check for leap cycle overflows and calculate the leap flag
         * if needed
@@ -665,11 +665,11 @@ ntpcal_split_eradays(
                        *isleapyear = 1;
        } else if (isleapyear)
                *isleapyear = (n001 == 3) && ((n004 != 24) || (n100 == 3));
-       
+
        /* now merge the cycles to elapsed years, using horner scheme */
        res.hi = ((4*n400 + n100)*25 + n004)*4 + n001;
        res.lo = yday;
-       
+
        return res;
 }
 
@@ -724,7 +724,13 @@ ntpcal_rd_to_date(
 
        leaps = 0;
        retv = 0;
-       /* get day-of-week first */
+       /* Get day-of-week first. Since rd is signed, the remainder can
+        * be in the range [-6..+6], but the assignment to an unsigned
+        * variable maps the negative values to positive values >=7.
+        * This makes the sign correction look strange, but adding 7
+        * causes the needed wrap-around into the desired value range of
+        * zero to six, both inclusive.
+        */
        jd->weekday = rd % 7;
        if (jd->weekday >= 7)   /* unsigned! */
                jd->weekday += 7;
@@ -794,7 +800,7 @@ ntpcal_daysec_to_date(
 {
        int32_t days;
        int   ts[3];
-       
+
        days = priv_timesplit(ts, sec);
        jd->hour   = (uint8_t)ts[0];
        jd->minute = (uint8_t)ts[1];
@@ -817,7 +823,7 @@ ntpcal_daysec_to_tm(
 {
        int32_t days;
        int32_t ts[3];
-       
+
        days = priv_timesplit(ts, sec);
        utm->tm_hour = ts[0];
        utm->tm_min  = ts[1];
@@ -946,7 +952,7 @@ ntpcal_dayjoin(
        /* fix sign */
        if (isneg)
                M_NEG(res.D_s.hi, res.D_s.lo);
-       
+
        /* properly add seconds */
        p2 = 0;
        if (secs < 0) {
@@ -957,7 +963,7 @@ ntpcal_dayjoin(
        }
        M_ADD(res.D_s.hi, res.D_s.lo, p2, p1);
 
-#endif 
+#endif
 
        return res;
 }
@@ -1279,7 +1285,7 @@ ntpcal_ntp64_to_date(
        )
 {
        ntpcal_split ds;
-       
+
        ds = ntpcal_daysplit(ntp);
        ds.hi += ntpcal_daysec_to_date(jd, ds.lo);
 
@@ -1294,7 +1300,7 @@ ntpcal_ntp_to_date(
        )
 {
        vint64  ntp64;
-       
+
        /*
         * Unfold ntp time around current time into NTP domain. Split
         * into days and seconds, shift days into CE domain and
@@ -1516,12 +1522,12 @@ isocal_split_eraweeks(
        res.lo += (res.lo >= 10435);
        cents   = res.lo / 5218;
        res.lo %= 5218;         /* res.lo is weeks in century now */
-       
+
        /* convert elapsed weeks in century to elapsed years and weeks */
        res.lo  = res.lo * 157 + bctab[cents];
        res.hi += cents * 100 + res.lo / 8192;
-       res.lo  = (res.lo % 8192) / 157;        
-       
+       res.lo  = (res.lo % 8192) / 157;
+
        return res;
 }
 
@@ -1538,7 +1544,7 @@ isocal_ntp64_to_date(
 {
        ntpcal_split ds;
        int32_t      ts[3];
-       
+
        /*
         * Split NTP time into days and seconds, shift days into CE
         * domain and process the parts.
@@ -1576,7 +1582,7 @@ isocal_ntp_to_date(
        )
 {
        vint64  ntp64;
-       
+
        /*
         * Unfold ntp time around current time into NTP domain, then
         * convert the full time stamp.