altos: Test APRS altitude encoding

Verify fixed point version against naïve implementation

Signed-off-by: Keith Packard <keithp@keithp.com>

1 files changed, 27 insertions, 0 deletions

diff --git a/src/test/ao_aprs_test.c b/src/test/ao_aprs_test.c
index b1d17d3f..86cf527a 100644
--- a/src/test/ao_aprs_test.c
+++ b/src/test/ao_aprs_test.c
@@ -97,9 +97,36 @@ audio_gap(int secs)
 #endif
 }
 
+#include <math.h>
+
+int
+ao_aprs_encode_altitude_expensive(int meters)
+{
+	double	feet = meters / 0.3048;
+
+	double	encode = log(feet) / log(1.002);
+	return floor(encode + 0.5);
+}
+
 // This is where we go after reset.
 int main(int argc, char **argv)
 {
+	int	e, x;
+	int	a;
+
+	for (a = 1; a < 100000; a++) {
+		e = ao_aprs_encode_altitude(a);
+		x = ao_aprs_encode_altitude_expensive(a);
+
+		if (e != x) {
+			double	back_feet, back_meters;
+			back_feet = pow(1.002, e);
+			back_meters = back_feet * 0.3048;
+			fprintf (stderr, "APRS altitude encoding failure: altitude %d actual %d expected %d actual meters %f\n",
+				 a, e, x, back_meters);
+		}
+	}
+
     audio_gap(1);
 
     ao_gps_data.latitude = (45.0 + 28.25 / 60.0) * 10000000;