[gnome-clocks] world: don't compute twilights were we can't

[Zander <zbrown src gnome org>]

commit 6bb7dc7c2eb66a9fd80905eaef3fdee15b99588d
Author: Manuel Genovés <manuel genoves gmail com>
Date:   Mon Apr 13 03:48:23 2020 +0200

    world: don't compute twilights were we can't
    
    More or less fixes #91
    
    This improves the handling of zones were we can't calculate twilight times,
    adding the corrections used for determining what type of twilight
    (civil/nautical/astronomical) and the corrections for the atmosphere's
    refraction to the calculation of the "out-of-bonds" region.
    
    We still should do some handling of these "out-of-bound" regions, since
    actually we just return sunrise: 00:00:00 / sunset : 12:59:59 without
    explicitly telling that those values are placeholder ones
    
    Signed-off-by: Manuel Genovés <manuel genoves gmail com>

 src/twilight.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)
---
diff --git a/src/twilight.c b/src/twilight.c
index a706a23..dced3d4 100644
--- a/src/twilight.c
+++ b/src/twilight.c
@@ -124,9 +124,10 @@ calculate_sunrise_sunset (double  lat,
 
   // IMPORTANT: for polar circles we can't compute anything for certain dates
 
-  if ((((is_in_north_summer (month) && (lat <= (d - 90))) || (lat >= (90 - d)))) ||
-      (((is_in_north_winter (month) && (lat <= (-d - 90))) || (lat >= (90 + d))))) {
-
+  if ((((is_in_north_summer (month) && (lat <= (d + 0.83 + correction - 90))) ||
+                                       (lat >= (90 - d - 0.83 - correction)))) ||
+      (((is_in_north_winter (month) && (lat <= (-90 - d - 0.83 - correction))) ||
+                                       (lat >= (90 + d + 0.83 + correction))))) {
     sunrise_hour = 0;
     sunrise_minute = 0;
     sunset_hour = 23;
@@ -141,7 +142,7 @@ calculate_sunrise_sunset (double  lat,
     // hour angle
     double w = DEGREES (acos ((sin (RADIANS (-correction)) + sin (RADIANS (-0.83)) -
                                sin (RADIANS (lat)) * sin (RADIANS (d)))
-                              / (cos (RADIANS (lat))) * cos (RADIANS (d))));
+                              / ((cos (RADIANS (lat))) * cos (RADIANS (d)))));
 
     // julian sunrise
     double J_sunrise = (J_transit - w / 360 - 0.5);