Need to duplicate new altitude conversion code in aoview.

Altitude conversion is now done with a smaller table and interpolation
instead of a giant table.

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

1 files changed, 34 insertions, 10 deletions

diff --git a/ao-tools/ao-view/aoview_convert.c b/ao-tools/ao-view/aoview_convert.c
index 02416647..8ee05e1d 100644
--- a/ao-tools/ao-view/aoview_convert.c
+++ b/ao-tools/ao-view/aoview_convert.c
@@ -17,26 +17,50 @@
 
 #include "aoview.h"
 
-static int16_t altitude_table[2048] = {
+static int16_t altitude_table[] = {
 #include "altitude.h"
 };
 
+#define ALT_FRAC_SCALE	(1 << ALT_FRAC_BITS)
+#define ALT_FRAC_MASK	(ALT_FRAC_SCALE - 1)
+
 int16_t
 aoview_pres_to_altitude(int16_t pres)
 {
-	pres = pres >> 4;
-	if (pres < 0) pres = 0;
-	if (pres > 2047) pres = 2047;
-	return altitude_table[pres];
+	uint8_t	o;
+	int16_t	part;
+
+	if (pres < 0)
+		pres = 0;
+	o = pres >> ALT_FRAC_BITS;
+	part = pres & ALT_FRAC_MASK;
+
+	return ((int32_t) altitude_table[o] * (ALT_FRAC_SCALE - part) +
+		(int32_t) altitude_table[o+1] * part + (ALT_FRAC_SCALE >> 1)) >> ALT_FRAC_BITS;
 }
 
 int16_t
 aoview_altitude_to_pres(int16_t alt)
 {
-	int16_t pres;
+	int16_t span, sub_span;
+	uint8_t	l, h, m;
+	int32_t pres;
 
-	for (pres = 0; pres < 2047; pres++)
-		if (altitude_table[pres] <= alt)
-			break;
-	return pres << 4;
+	l = 0;
+	h = NALT - 1;
+	while ((h - l) != 1) {
+		m = (l + h) >> 1;
+		if (altitude_table[m] < alt)
+			h = m;
+		else
+			l = m;
+	}
+	span = altitude_table[l] - altitude_table[h];
+	sub_span = altitude_table[l] - alt;
+	pres = ((((int32_t) l * (span - sub_span) + (int32_t) h * sub_span) << ALT_FRAC_BITS) + (span >> 1)) / span;
+	if (pres > 32767)
+		pres = 32767;
+	if (pres < 0)
+		pres = 0;
+	return (int16_t) pres;
 }