Adding unit test for some gps conversion code to demystify it.

Makefile

@@ -116,6 +116,7 @@ COMMON_SRC	 = build_config.c \
 		   flight_imu.c \
 		   flight_mixer.c \
 		   gps_common.c \
+		   gps_conversion.c \
 		   runtime_config.c \
 		   rc_controls.c \
 		   rc_curves.c \

src/gps_common.c

@@ -25,6 +25,7 @@
 #include "config.h"
 #include "runtime_config.h"
 
+#include "gps_conversion.h"
 #include "gps_common.h"
 
 extern int16_t debug[4];
@@ -925,47 +926,6 @@ static uint32_t GPS_coord_to_degrees(char *s)
 }
 */
 
-#define DIGIT_TO_VAL(_x)    (_x - '0')
-uint32_t GPS_coord_to_degrees(char* s)
-{
-    char *p, *q;
-    uint8_t deg = 0, min = 0;
-    unsigned int frac_min = 0;
-    int i;
-
-    // scan for decimal point or end of field
-    for (p = s; isdigit((unsigned char)*p); p++) {
-        if (p >= s + 15)
-            return 0; // stop potential fail
-    }
-    q = s;
-
-    // convert degrees
-    while ((p - q) > 2) {
-        if (deg)
-            deg *= 10;
-        deg += DIGIT_TO_VAL(*q++);
-    }
-    // convert minutes
-    while (p > q) {
-        if (min)
-            min *= 10;
-        min += DIGIT_TO_VAL(*q++);
-    }
-    // convert fractional minutes
-    // expect up to four digits, result is in
-    // ten-thousandths of a minute
-    if (*p == '.') {
-        q = p + 1;
-        for (i = 0; i < 4; i++) {
-            frac_min *= 10;
-            if (isdigit((unsigned char)*q))
-                frac_min += *q++ - '0';
-        }
-    }
-    return deg * 10000000UL + (min * 1000000UL + frac_min * 100UL) / 6;
-}
-
 // helper functions
 static uint32_t grab_fields(char *src, uint8_t mult)
 {                               // convert string to uint32

src/gps_conversion.c

@@ -0,0 +1,46 @@
+#include <stdbool.h>
+#include <stdint.h>
+#include <ctype.h>
+#include <string.h>
+
+
+#define DIGIT_TO_VAL(_x)    (_x - '0')
+uint32_t GPS_coord_to_degrees(char* coordinateString)
+{
+    char *fieldSeparator, *remainingString;
+    uint8_t degress = 0, minutes = 0;
+    uint16_t fractionalMinutes = 0;
+    uint8_t digitIndex;
+
+    // scan for decimal point or end of field
+    for (fieldSeparator = coordinateString; isdigit((unsigned char)*fieldSeparator); fieldSeparator++) {
+        if (fieldSeparator >= coordinateString + 15)
+            return 0; // stop potential fail
+    }
+    remainingString = coordinateString;
+
+    // convert degrees
+    while ((fieldSeparator - remainingString) > 2) {
+        if (degress)
+            degress *= 10;
+        degress += DIGIT_TO_VAL(*remainingString++);
+    }
+    // convert minutes
+    while (fieldSeparator > remainingString) {
+        if (minutes)
+            minutes *= 10;
+        minutes += DIGIT_TO_VAL(*remainingString++);
+    }
+    // convert fractional minutes
+    // expect up to four digits, result is in
+    // ten-thousandths of a minute
+    if (*fieldSeparator == '.') {
+        remainingString = fieldSeparator + 1;
+        for (digitIndex = 0; digitIndex < 4; digitIndex++) {
+            fractionalMinutes *= 10;
+            if (isdigit((unsigned char)*remainingString))
+                fractionalMinutes += *remainingString++ - '0';
+        }
+    }
+    return degress * 10000000UL + (minutes * 1000000UL + fractionalMinutes * 100UL) / 6;
+}

src/gps_conversion.h

@@ -0,0 +1 @@
+uint32_t GPS_coord_to_degrees(char* s);

test/Makefile

@@ -26,11 +26,11 @@ TEST_DIR = .
 CPPFLAGS += -isystem $(GTEST_DIR)/inc
 
 # Flags passed to the C++ compiler.
-CXXFLAGS += -g -Wall -Wextra -pthread
+CXXFLAGS += -g -Wall -Wextra -pthread -ggdb -O0
 
 # All tests produced by this Makefile.  Remember to add new tests you
 # created to the list.
-TESTS = battery_unittest flight_imu_unittest
+TESTS = battery_unittest flight_imu_unittest gps_conversion_unittest
 
 # All Google Test headers.  Usually you shouldn't change this
 # definition.
@@ -96,3 +96,14 @@ flight_imu_unittest.o : $(TEST_DIR)/flight_imu_unittest.cc \
 flight_imu_unittest : flight_imu.o flight_imu_unittest.o gtest_main.a
 	$(CXX) $(CPPFLAGS) $(CXXFLAGS) -lpthread $^ -o $@
 
+
+gps_conversion.o : $(USER_DIR)/gps_conversion.c $(USER_DIR)/gps_conversion.h $(GTEST_HEADERS)
+	$(CXX) $(CPPFLAGS) $(CXXFLAGS) -c $(USER_DIR)/gps_conversion.c -I$(TEST_DIR)
+
+gps_conversion_unittest.o : $(TEST_DIR)/gps_conversion_unittest.cc \
+                     $(USER_DIR)/gps_conversion.h $(GTEST_HEADERS)
+	$(CXX) $(CPPFLAGS) $(CXXFLAGS) -c $(TEST_DIR)/gps_conversion_unittest.cc -I$(USER_DIR)
+
+gps_conversion_unittest : gps_conversion.o gps_conversion_unittest.o gtest_main.a
+	$(CXX) $(CPPFLAGS) $(CXXFLAGS) -lpthread $^ -o $@
+

test/gps_conversion_unittest.cc

@@ -0,0 +1,50 @@
+#include <stdint.h>
+
+#include <limits.h>
+#include "gps_conversion.h"
+
+#include "unittest_macros.h"
+#include "gtest/gtest.h"
+
+// See http://en.wikipedia.org/wiki/Geographic_coordinate_conversion
+
+TEST(GpsConversionTest, GPSCoordToDegrees_BadString)
+{
+    // expect
+    uint32_t result = GPS_coord_to_degrees("diediedie");
+    EXPECT_EQ(result, 0);
+}
+
+typedef struct gpsConversionExpectation_s {
+    char *coord;
+    uint32_t degrees;
+} gpsConversionExpectation_t;
+
+TEST(GpsConversionTest, GPSCoordToDegrees_NMEA_Values)
+{
+    gpsConversionExpectation_t gpsConversionExpectations[] = {
+        {"0.0", 0},
+        {"000.0", 0},
+        {"00000.0000", 0},
+        {"0.0001", 16}, // smallest value
+        {"25599.9999", 2566666650}, // largest value
+        {"25599.99999", 2566666650}, // too many fractional digits
+        {"25699.9999", 16666650}, // overflowed without detection
+        {"5321.6802", 533613366},
+        {"00630.3372", 65056200},
+    };
+
+    // expect
+
+    uint8_t testIterationCount = sizeof(gpsConversionExpectations) / sizeof(gpsConversionExpectation_t);
+
+    // expect
+
+    for (uint8_t index = 0; index < testIterationCount; index ++) {
+        gpsConversionExpectation_t *expectation = &gpsConversionExpectations[index];
+        printf("iteration: %d\n", index);
+
+        uint32_t result = GPS_coord_to_degrees(expectation->coord);
+        EXPECT_EQ(result, expectation->degrees);
+    }
+}