1 files changed, 101 insertions, 0 deletions
diff --git a/src/cmd/scat/patch.c b/src/cmd/scat/patch.c
new file mode 100644
index 00000000..27d04edb
--- /dev/null
+++ b/src/cmd/scat/patch.c
@@ -0,0 +1,101 @@
+#include <u.h>
+#include <libc.h>
+#include	<bio.h>
+#include "sky.h"
+
+/*
+ * dec varies from -89 to 89, inclusive.
+ * ra varies depending on dec; each patch is about 1 square degree.
+ *
+ * Northern hemisphere (0<=dec<=89):
+ *	from  0<=dec<=59, ra is every 4m,  360 values
+ *	from 60<=dec<=69, ra is every 8m,  180 values
+ *	from 70<=dec<=79, ra is every 12m, 120 values
+ *	from 80<=dec<=84, ra is every 24m,  60 values
+ *	at dec=85 and 86, ra is every 48m,  30 values
+ *	at dec=87,        ra is every 60m,  24 values
+ *	at dec=88,        ra is every 120m, 12 values
+ *	at dec=89,        ra is 12h,	     1 value
+ *
+ * Total number of patches in northern hemisphere is therefore:
+ * 	360*60+180*10+120*10+60*5+30*2+24*1+12*1+1 = 24997
+ * Total number of patches is therefore
+ *	2*24997-360 = 49634	(dec=0 has been counted twice)
+ * (cf. 41253 square degrees in the sky)
+ */
+
+void
+radec(int p, int *rah, int *ram, int *deg)
+{
+	*deg = (p&255)-90;
+	p >>= 8;
+	*rah = p/15;
+	*ram = (p%15)*4;
+	if(*deg<0)
+		(*deg)++;
+}
+
+long
+patcha(Angle ra, Angle dec)
+{
+	ra = DEG(ra);
+	dec = DEG(dec);
+	if(dec >= 0)
+		return patch(floor(ra/15), ((int)floor(ra*4))%60, floor(dec));
+	dec = -dec;
+	return patch(floor(ra/15), ((int)floor(ra*4))%60, -floor(dec));
+}
+
+#define round scatround
+
+char round[91]={	/* extra 0 is to offset the array */
+	/*  0 */    0,	 1,  1,  1,  1,  1,  1,  1,  1,  1,  1,
+	/* 10 */	 1,  1,  1,  1,  1,  1,  1,  1,  1,  1,
+	/* 20 */	 1,  1,  1,  1,  1,  1,  1,  1,  1,  1,
+	/* 30 */	 1,  1,  1,  1,  1,  1,  1,  1,  1,  1,
+	/* 40 */	 1,  1,  1,  1,  1,  1,  1,  1,  1,  1,
+	/* 50 */	 1,  1,  1,  1,  1,  1,  1,  1,  1,  1,
+	/* 60 */	 2,  2,  2,  2,  2,  2,  2,  2,  2,  2,
+	/* 70 */	 3,  3,  3,  3,  3,  3,  3,  3,  3,  3,
+	/* 80 */	 6,  6,  6,  6,  6, 12, 12, 15, 30, -1,
+	/* 90 */
+};
+
+long
+patch(int rah, int ram, int deg)
+{
+	int ra, dec;
+
+	/*
+	 * patches go from lower limit <= position < upper limit.
+	 * therefore dec ' " can be ignored; always inc. dec degrees.
+	 * the computed angle is then the upper limit (ignoring sign).
+	 * when done, +ve values are shifted down so 90 (0 degrees) is a value;
+	 */
+	if(rah<0 || rah>=24 || ram<0 || abs(deg)>=90){
+		fprint(2, "scat: patch: bad ra or dec %dh%dm %d\n", rah, ram, deg);
+		abort();
+	}
+	if(deg < 0)
+		deg--;
+	else if(deg < 90)
+		deg++;
+	dec = deg+90;
+	deg = abs(deg);
+	if(deg<1 || deg>90){
+		fprint(2, "scat: patch: panic %dh%dm %d\n", rah, ram, deg);
+		abort();
+	}
+	if(deg == 90)
+		ra = 180;
+	else{
+		ra = 15*rah+ram/4;
+		ra -= ra%round[deg];
+	}
+	/* close the hole at 0 */
+	if(dec > 90)
+		--dec;
+	if(ra >= 360)
+		ra -= 360;
+	return (ra<<8)|dec;
+}