Use more libm.

adj360() is a modulo operation: use fmod(3) to simplify things.

Adding 0.5 to the phase to steer implicit truncation is a hack:
use lround(3) to simplify things.

Product of a discussion with pjanzen@/jca@/tb@ regarding floating-point
rounding and the importance of correctly classifying a gibbous moon.

ok pjanzen@ jca@ tb@

diff --git a/games/pom/pom.c b/games/pom/pom.c
index b57214e..31d43a6 100644 (file)
--- a/games/pom/pom.c
+++ b/games/pom/pom.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: pom.c,v 1.26 2017/12/23 20:53:07 cheloha Exp $        */
+/*     $OpenBSD: pom.c,v 1.27 2017/12/24 16:59:50 cheloha Exp $        */
 /*    $NetBSD: pom.c,v 1.6 1996/02/06 22:47:29 jtc Exp $      */
 
 /*
@@ -96,28 +96,24 @@ main(int argc, char *argv[])
        /* Selected time could be before EPOCH */
        for (cnt = GMT->tm_year; cnt < EPOCH; ++cnt)
                days -= isleap(cnt + 1900) ? 366 : 365;
-       today = potm(days) + 0.5;
+       today = potm(days);
        (void)printf("The Moon is ");
-       if ((int)today == 100)
+       if (lround(today) == 100)
                (void)printf("Full\n");
-       else if (!(int)today)
+       else if (lround(today) == 0)
                (void)printf("New\n");
        else {
                tomorrow = potm(days + 1);
-               if ((int)today == 50)
+               if (lround(today) == 50)
                        (void)printf("%s\n", tomorrow > today ?
                            "at the First Quarter" : "at the Last Quarter");
-                       /* today is 0.5 too big, but it doesn't matter here
-                        * since the phase is changing fast enough
-                        */
                else {
-                       today -= 0.5;           /* Now it might matter */
                        (void)printf("%s ", tomorrow > today ?
                            "Waxing" : "Waning");
-                       if (today > 50)
+                       if (today > 50.0)
                                (void)printf("Gibbous (%1.0f%% of Full)\n",
                                    today);
-                       else if (today < 50)
+                       else /* (today < 50.0) */
                                (void)printf("Crescent (%1.0f%% of Full)\n",
                                    today);
                }
@@ -178,13 +174,9 @@ dtor(double deg)
 void
 adj360(double *deg)
 {
-       for (;;)
-               if (*deg < 0.0)
-                       *deg += 360.0;
-               else if (*deg > 360.0)
-                       *deg -= 360.0;
-               else
-                       break;
+       *deg = fmod(*deg, 360.0);
+       if (*deg < 0.0)
+               *deg += 360.0;
 }
 
 #define        ATOI2(ar)       ((ar)[0] - '0') * 10 + ((ar)[1] - '0'); (ar) += 2;