lib/datetime: Reduce cognitive complexity of core datetime functions

lib/datetime/change.c

 return 0; 
 /* set the new elements to zero */ 
 for (pos = from; pos < dtfrom; pos++) 
     switch (pos) { 
     case DATETIME_YEAR: 
         dt->year = 0; 
         break; 
     case DATETIME_MONTH: 
         dt->month = 0; 
         break; 
     case DATETIME_DAY: 
         dt->day = 0; 
         break; 
     case DATETIME_HOUR: 
         dt->hour = 0; 
         break; 
     case DATETIME_MINUTE: 
         dt->minute = 0; 
         break; 
     case DATETIME_SECOND: 
         dt->second = 0; 
         break; 
 for (pos = to; pos > dt->to; pos--) 
     switch (pos) { 
     case DATETIME_YEAR: 
         dt->year = 0; 
         break; 
     case DATETIME_MONTH: 
         dt->month = 0; 
         break; 
     case DATETIME_DAY: 
         dt->day = 0; 
         break; 
     case DATETIME_HOUR: 
         dt->hour = 0; 
         break; 
     case DATETIME_MINUTE: 
         dt->minute = 0; 
         break; 
     case DATETIME_SECOND: 
         dt->second = 0; 
         break; 
 /* make sure that fracsec is zero if original didn't have seconds */ 
 if (dt->to < DATETIME_SECOND) 
     dt->fracsec = 0; 
 /* now set the to */ 
 dt->to = to; 
 return 0; 
@@ -5,9 +5,66 @@
  * Read the file GPL.TXT coming with GRASS for details.
  */
 #include <grass/datetime.h>
-
 static void make_incr(DateTime *, int, int, DateTime *);
 
+/* Handles the "round == 0" branch for (to < dt->to): increment using all lost values */
+static void apply_round0_lost(DateTime *dt, int to, DateTime *incr)
+{
+    int pos;
+    int ndays;
+
+    if (datetime_is_absolute(dt))
+        ndays = datetime_days_in_year(dt->year, dt->positive);
+    else
+        ndays = 0;
+
+    for (pos = dt->to; pos > to; pos--) {
+        make_incr(incr, pos, pos, dt);
+        incr->year = dt->year;
+        incr->month = dt->month;
+        incr->day = dt->day + ndays / 2;
+        incr->hour = dt->hour;
+        incr->minute = dt->minute;
+        incr->second = dt->second;
+
+        datetime_increment(dt, incr);
+
+        if (ndays > 0 && pos == DATETIME_DAY)
+            break;
+    }
+}
+/* Returns 1 if any “lost” component between dt->to down to (to+1) is non-default */
+static int has_lost_non_default(const DateTime *dt, int to, int x)
+{
+    int pos;
+
+    for (pos = dt->to; pos > to; pos--) {
+        switch (pos) {
+        case DATETIME_MONTH:
+            if (dt->month != x)
+                return 1;
+            break;
+        case DATETIME_DAY:
+            if (dt->day != x)
+                return 1;
+            break;
+        case DATETIME_HOUR:
+            if (dt->hour != x)
+                return 1;
+            break;
+        case DATETIME_MINUTE:
+            if (dt->minute != x)
+                return 1;
+            break;
+        case DATETIME_SECOND:
+            if (dt->second != (double)x)
+                return 1;
+            break;
+        }
+    }
+    return 0;
+}
+
 /*!
  * \brief
  *
@@ -101,78 +158,35 @@ int datetime_change_from_to(DateTime *dt, int from, int to, int round)
         }
     }
 
-    /* if losing precision, round
-     *    round > 0 force up if any lost values not zero
-     *    round ==0 increment by all lost values
-     */
-    if (to < dt->to) {
-        if (round > 0) {
-            int x;
-
-            x = datetime_is_absolute(dt) ? 1 : 0;
-
-            for (carry = 0, pos = dt->to; carry == 0 && pos > to; pos--) {
-                switch (pos) {
-                case DATETIME_MONTH:
-                    if (dt->month != x)
-                        carry = 1;
-                    break;
-                case DATETIME_DAY:
-                    if (dt->day != x)
-                        carry = 1;
-                    break;
-                case DATETIME_HOUR:
-                    if (dt->hour != 0)
-                        carry = 1;
-                    break;
-                case DATETIME_MINUTE:
-                    if (dt->minute != 0)
-                        carry = 1;
-                    break;
-                case DATETIME_SECOND:
-                    if (dt->second != 0)
-                        carry = 1;
-                    break;
-                }
-            }
-
-            if (carry) {
-                make_incr(&incr, to, to, dt);
-
-                incr.year = 1;
-                incr.month = 1;
-                incr.day = 1;
-                incr.hour = 1;
-                incr.minute = 1;
-                incr.second = 1.0;
-
-                datetime_increment(dt, &incr);
-            }
-        }
-
-        if (round == 0) {
-            /*NEW*/ if (datetime_is_absolute(dt))
-                /*NEW*/ ndays = datetime_days_in_year(dt->year, dt->positive);
-            /*NEW*/
-            else
-                /*NEW*/ ndays = 0;
-
-            for (pos = dt->to; pos > to; pos--) {
-                make_incr(&incr, pos, pos, dt);
-
-                incr.year = dt->year;
-                incr.month = dt->month;
-                /*NEW*/ incr.day = dt->day + ndays / 2;
-                incr.hour = dt->hour;
-                incr.minute = dt->minute;
-                incr.second = dt->second;
-
-                datetime_increment(dt, &incr);
-                /*NEW*/ if (ndays > 0 && pos == DATETIME_DAY)
-                    /*NEW*/ break;
-            }
-        }
+static void round_lost_precision(DateTime *dt, int to, int round)
+ {
+     DateTime incr;
+     int pos, carry, ndays;
+
+     if (to >= dt->to)
+         return;
+
+     if (round > 0) {
+         int x = datetime_is_absolute(dt) ? 1 : 0;
+
+            carry = has_lost_non_default(dt, to, x);
+         }
+
+         if (carry) {
+             make_incr(&incr, to, to, dt);
+             incr.year = 1; incr.month = 1; incr.day = 1;
+             incr.hour = 1; incr.minute = 1; incr.second = 1.0;
+             datetime_increment(dt, &incr);
+         }
+     }
+
+     if (round == 0) {
+         apply_round0_lost(dt, to, &incr);
     }
+ }
+
+
+    round_lost_precision(dt, to, round);
 
     /* set the new elements to zero */
     for (pos = from; pos < dtfrom; pos++)

lib/datetime/diff.c

@@ -183,68 +183,42 @@ static int _datetime_compare(const DateTime *a, const DateTime *b)
     int i;
 
     if (a->positive && !b->positive)
-        return (1);
-    else if (b->positive && !a->positive)
-        return (-1);
+        return 1;
+    if (b->positive && !a->positive)
+        return -1;
 
-    /* same signs */
     for (i = a->from; i <= a->to; i++) {
-        switch (i) {
+        int c = 0;
 
+        switch (i) {
         case DATETIME_SECOND:
-            if (a->second > b->second)
-                return (1);
-            else if (a->second < b->second)
-                return (-1);
+            c = (a->second > b->second) - (a->second < b->second);
             break;
-
         case DATETIME_MINUTE:
-            if (a->minute > b->minute)
-                return (1);
-            else if (a->minute < b->minute)
-                return (-1);
+            c = cmp_int(a->minute, b->minute);
             break;
-
         case DATETIME_HOUR:
-            if (a->hour > b->hour)
-                return (1);
-            else if (a->hour < b->hour)
-                return (-1);
+            c = cmp_int(a->hour, b->hour);
             break;
-
         case DATETIME_DAY:
-            if (a->day > b->day)
-                return (1);
-            else if (a->day < b->day)
-                return (-1);
+            c = cmp_int(a->day, b->day);
             break;
-
         case DATETIME_MONTH:
-            if (a->month > b->month)
-                return (1);
-            else if (a->month < b->month)
-                return (-1);
+            c = cmp_int(a->month, b->month);
             break;
-
         case DATETIME_YEAR: /* only place sign matters */
-            if (a->positive) {
-                if (a->year > b->year)
-                    return (1);
-                else if (a->year < b->year)
-                    return (-1);
-            }
-            else {
-                if (a->year < b->year)
-                    return (1);
-                else if (a->year > b->year)
-                    return (-1);
-            }
+            c = cmp_year_signed(a, b);
             break;
         }
+
+        if (c != 0)
+            return c;
     }
-    return (0);
+
+    return 0;
 }
 
+
 /*************************************************************/
 
 static int _datetime_ymd_to_ddays(const DateTime *dtymd, double *days)