Move Hagelbarger error correction code from NMT to common code

It will be used by Radiocom 2000 also.
Some minor fixes and improvements apply.

src/common/Makefile.am

@@ -25,6 +25,7 @@ libcommon_a_SOURCES = \
 	fft.c \
 	fm_modulation.c \
 	ffsk.c \
+	hagelbarger.c \
 	sender.c \
 	display_wave.c \
 	display_status.c \

src/common/hagelbarger.c

@@ -27,10 +27,13 @@
 
 #include "stdint.h"
 
+/* enable to debug the process of parity check */
+//#define DEBUG_HAGEL
+
 /* To encode NMT message: (MSB first)
  * Use input with 9 bytes, the last byte must be 0x00.
  * Use output with 18 bytes, ignore the last four (lower) bits of last byte.
- * Use length of 72.
+ * Use length of 70.
  */
 void hagelbarger_encode(const uint8_t *input, uint8_t *output, int length)
 {
@@ -49,6 +52,9 @@ void hagelbarger_encode(const uint8_t *input, uint8_t *output, int length)
 		/* put check bit and data bit to output (MSB first) */
 		output[i / 4] = (output[i / 4] << 2) | (check << 1) | data;
 	}
+	/* shift last output byte all the way to MSB */
+	while ((i % 4))
+		output[i++ / 4] <<= 2;
 }
 
 /* To decode NMT message: (MSB first)
@@ -58,12 +64,12 @@ void hagelbarger_encode(const uint8_t *input, uint8_t *output, int length)
  */
 void hagelbarger_decode(const uint8_t *input, uint8_t *output, int length)
 {
-	uint16_t reg_data = 0x00, reg_check = 0x00, data, check, r_parity, s_parity;
-	int i;
+	uint16_t reg_data = 0x00, reg_check = 0xff, data, check, r_parity, s_parity;
+	int i, o;
 
 	length += 10;
 
-	for (i = 0; i < length; i++) {
+	for (i = 0, o = 0; i < length; i++) {
 		/* get check bit from input (MSB first) */
 		check = (input[i / 4] >> (7 - (i & 3) * 2)) & 1;
 		/* get data bit from input (MSB first) */
@@ -75,13 +81,21 @@ void hagelbarger_decode(const uint8_t *input, uint8_t *output, int length)
 		/* calculate parity */
 		r_parity = (reg_data + (reg_data >> 3) + (reg_check >> 6) + 1) & 1;
 		s_parity = ((reg_data >> 3) + (reg_data >> 6) + (reg_check >> 9) + 1) & 1;
+#ifdef DEBUG_HAGEL
+		printf("#%d: r=%d s=%d\n", i - 10, r_parity, s_parity);
+#endif
 		/* flip message bit, if both parity checks fail */
 		/* use 4th bit that will be shifted to 5th bit next loop */
 		if (r_parity && s_parity)
 			reg_data ^= 0x0008;
 		/* put message bit to output (MSB first) */
-		if (i >= 10)
-			output[(i - 10) / 8] = (output[(i - 10) / 8] << 1) | ((reg_data >> 4) & 1);
+		if (i >= 10) {
+			output[o / 8] = (output[o / 8] << 1) | ((reg_data >> 4) & 1);
+			o++;
+		}
 	}
+	/* shift last output byte all the way to MSB */
+	while ((o % 8))
+		output[o++ / 8] <<= 1;
 }
 

src/nmt/Makefile.am

@@ -8,7 +8,6 @@ nmt_SOURCES = \
 	countries.c \
 	transaction.c \
 	dsp.c \
-	hagelbarger.c \
 	frame.c \
 	dms.c \
 	sms.c \

src/nmt/frame.c

@@ -25,9 +25,9 @@
 #include "../common/sample.h"
 #include "../common/debug.h"
 #include "../common/timer.h"
+#include "../common/hagelbarger.h"
 #include "nmt.h"
 #include "frame.h"
-#include "hagelbarger.h"
 
 uint64_t nmt_encode_channel(int nmt_system, int channel, int power)
 {
@@ -1146,7 +1146,7 @@ const char *encode_frame(int nmt_system, frame_t *frame, int debug)
 	message[8] = 0x00;
 	for (i = 0; i < 8; i++)
 		message[i] = (digits[i * 2] << 4) | digits[i * 2 + 1];
-	hagelbarger_encode(message, code, 72);
+	hagelbarger_encode(message, code, 70);
 	memcpy(bits, "10101010101010111100010010", 26);
 	for (i = 0; i < 140; i++)
 		bits[i + 26] = ((code[i / 8] >> (7 - (i & 7))) & 1) + '0';

src/test/Makefile.am

@@ -79,7 +79,7 @@ test_performance_LDADD = \
 	-lm
 
 test_hagelbarger_SOURCES = \
-	$(top_builddir)/src/nmt/hagelbarger.c \
+	$(top_builddir)/src/common/hagelbarger.c \
 	test_hagelbarger.c
 
 test_hagelbarger_LDADD = \

src/test/test_hagelbarger.c

@@ -1,7 +1,7 @@
 #include "stdio.h"
 #include "stdint.h"
 #include "string.h"
-#include "../nmt/hagelbarger.h"
+#include "../common/hagelbarger.h"
 
 int main(void)
 {
@@ -9,11 +9,15 @@ int main(void)
 
 	printf("Message: %s\n", message);
 
-	/* clean tail at code bit 72 and above */
+	/* clean tail at code bit 70 and above */
 	memset(code, 0, sizeof(code));
 
 	/* encode message */
-	hagelbarger_encode(message, code, 72);
+	hagelbarger_encode(message, code, 70);
+
+	/* decode */
+	hagelbarger_decode(code, message, 64);
+	printf("Decoded without corruption: %s (must be the same as above)\n", message);
 
 	/* corrupt data */
 	code[0] ^= 0xfc;
@@ -22,7 +26,7 @@ int main(void)
 
 	/* decode */
 	hagelbarger_decode(code, message, 64);
-	printf("Decoded: %s (must be the same as above)\n", message);
+	printf("Decoded with corruption: %s (must be the same as above)\n", message);
 
 	return 0;
 }