Fix determining intermediate frequency for C-band LNBs

Closes #1146

src/adapter.c

@@ -1224,9 +1224,9 @@ int get_lnb_int_freq(transponder *tp, diseqc *diseqc_param) {
 
     if (tp->pol > 2 && diseqc_param->lnb_circular > 0)
         return (freq - diseqc_param->lnb_circular);
-    if (freq < diseqc_param->lnb_switch)
-        return (freq - diseqc_param->lnb_low);
-    return (freq - diseqc_param->lnb_high);
+    if (diseqc_param->lnb_switch > 0 && freq > diseqc_param->lnb_switch)
+        return (freq - diseqc_param->lnb_high);
+    return abs(freq - diseqc_param->lnb_low);
 }
 
 int compare_tunning_parameters(int aid, transponder *tp) {

src/minisatip.c

@@ -404,8 +404,11 @@ Help\n\
 \n\
 * -L --lnb specifies the adapter and LNB parameters (low, high and switch frequency)\n\
 	* eg: -L *:9750-10600-11700 - sets all the adapters to use Universal LNB parameters (default)\n\
-	* eg: -L *:10750-10750-10750 - sets the parameters for Sky NZ LNB using 10750 Mhz\n\
-	* eg: -L 0:10750-10750-10750,1:9750-10600-11700 - adapter 0 has a SKY NZ LNB, adapter 1 has an Universal LNB\n\
+	* eg: -L *:10750-0-0 - sets all adapters to use 10750 MHz Ku-band LNB parameters (e.g. Sky NZ)\n\
+    * eg: -L *:5150-0-0 - sets all adapters to use 5150 MHz C-band LNB parameters\n\
+	* eg: -L 0:10750-0-0,1:9750-10600-11700 - adapter 0 has a SKY NZ LNB, adapter 1 has an Universal LNB\n\
+    \n\
+    For backward-compatibility reasons, linear LNB parameters may also be specified as *:5150-5150-5150 instead of *:5150-0-0\n\
 \n\
 * -m --mac xx: simulate xx as local mac address, generates UUID based on mac\n\
 	* eg: -m 001122334455 \n\

tests/Makefile.in

@@ -15,6 +15,7 @@ else
 endif
 
 SOURCES=\
+	test_adapter.c \
 	test_opts.c \
 	test_ca.c \
 	test_pmt.c \

tests/test_adapter.c

@@ -0,0 +1,99 @@
+/*
+ * Copyright (C) 2014-2022 Catalin Toda <catalinii@yahoo.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
+ * USA
+ *
+ */
+#define _GNU_SOURCE
+
+#include "adapter.h"
+#include "minisatip.h"
+#include "utils.h"
+#include "utils/testing.h"
+
+#include <string.h>
+#include <linux/dvb/frontend.h>
+
+int test_get_lnb_hiband() {
+  return 0;
+}
+
+int test_get_lnb_int_freq_universal() {
+  transponder tp;
+  diseqc diseqc_param = {
+    .lnb_low = 9750000,
+    .lnb_high = 10600000,
+    .lnb_switch = 11700000
+  };
+
+  tp.freq = 10778000;
+  int freq = get_lnb_int_freq(&tp, &diseqc_param);
+  ASSERT(freq == 1028000, "Universal LNB IF parsed incorrectly");
+
+  tp.freq = 12322000;
+  freq = get_lnb_int_freq(&tp, &diseqc_param);
+  ASSERT(freq == 1722000, "Universal LNB IF parsed incorrectly");
+
+  return 0;
+}
+
+int test_get_lnb_int_freq_kuband() {
+  transponder tp;
+  diseqc diseqc_param = {
+    .lnb_low = 10750000,
+    .lnb_high = 0,
+    .lnb_switch = 0,
+  };
+
+  tp.freq = 12267000;
+  int freq = get_lnb_int_freq(&tp, &diseqc_param);
+  ASSERT(freq == 1517000, "Ku-band LNB IF parsed incorrectly");
+
+  return 0;
+}
+
+int test_get_lnb_int_freq_cband() {
+  transponder tp;
+  diseqc diseqc_param = {
+    .lnb_low = 5150000,
+    .lnb_high = 0,
+    .lnb_switch = 0
+  };
+
+  tp.freq = 3773000;
+  int freq = get_lnb_int_freq(&tp, &diseqc_param);
+  ASSERT(freq == 1377000, "C-band LNB IF parsed incorrectly");
+
+  // Should also work with low = high = switch
+  diseqc_param.lnb_high = diseqc_param.lnb_switch = 5150000;
+  freq = get_lnb_int_freq(&tp, &diseqc_param);
+  ASSERT(freq == 1377000, "C-band LNB IF parsed incorrectly");
+
+  return 0;
+}
+
+int main() {
+  opts.log = 1;
+  opts.debug = 255;
+  strcpy(thread_info[thread_index].thread_name, "test_adapter");
+
+  TEST_FUNC(test_get_lnb_hiband(), "test test_get_lnb_hiband with universal LNB parameters");
+  TEST_FUNC(test_get_lnb_int_freq_universal(), "test get_lnb_int_freq with universal LNB parameters");
+  TEST_FUNC(test_get_lnb_int_freq_kuband(), "test get_lnb_int_freq with typical Ku-band linear LNB parameters");
+  TEST_FUNC(test_get_lnb_int_freq_cband(), "test get_lnb_int_freq with C-band LNB parameters");
+
+  return 0;
+}