Move zigzag encoding function to new common/encoding.c file, add tests

Makefile

@@ -199,6 +199,7 @@ COMMON_SRC	 = build_config.c \
 		   common/maths.c \
 		   common/printf.c \
 		   common/typeconversion.c \
+		   common/encoding.c \
 		   main.c \
 		   mw.c \
 		   flight/altitudehold.c \

src/main/blackbox/blackbox.c

@@ -26,6 +26,7 @@
 #include "common/maths.h"
 #include "common/axis.h"
 #include "common/color.h"
+#include "common/encoding.h"
 
 #include "drivers/gpio.h"
 #include "drivers/sensor.h"
@@ -878,11 +879,6 @@ static bool sendFieldDefinition(const char * const *headerNames, unsigned int he
  */
 static bool blackboxWriteSysinfo()
 {
-    union floatConvert_t {
-        float f;
-        uint32_t u;
-    } floatConvert;
-
     if (xmitState.headerIndex == 0) {
         xmitState.u.serialBudget = 0;
         xmitState.headerIndex = 1;
@@ -937,8 +933,7 @@ static bool blackboxWriteSysinfo()
             xmitState.u.serialBudget -= strlen("H maxthrottle:%d\n");
         break;
         case 8:
-            floatConvert.f = gyro.scale;
+            blackboxPrintf("H gyro.scale:0x%x\n", castFloatBytesToInt(gyro.scale));
-            blackboxPrintf("H gyro.scale:0x%x\n", floatConvert.u);
 
             xmitState.u.serialBudget -= strlen("H gyro.scale:0x\n") + 6;
         break;

src/main/blackbox/blackbox_io.c

@@ -4,12 +4,13 @@
 
 #include "blackbox_io.h"
 
-#include "platform.h"
 #include "version.h"
+#include "build_config.h"
 
 #include "common/maths.h"
 #include "common/axis.h"
 #include "common/color.h"
+#include "common/encoding.h"
 
 #include "drivers/gpio.h"
 #include "drivers/sensor.h"
@@ -144,18 +145,6 @@ void blackboxWriteUnsignedVB(uint32_t value)
     blackboxWrite(value);
 }
 
-/**
- * ZigZag encoding maps all values of a signed integer into those of an unsigned integer in such
- * a way that numbers of small absolute value correspond to small integers in the result.
- *
- * (Compared to just casting a signed to an unsigned which creates huge resulting numbers for
- * small negative integers).
- */
-static uint32_t zigzagEncode(int32_t value)
-{
-    return (uint32_t)((value << 1) ^ (value >> 31));
-}
-
 /**
  * Write a signed integer to the blackbox serial port using ZigZig and variable byte encoding.
  */

src/main/blackbox/blackbox_io.h

@@ -20,7 +20,7 @@
 #include <stdint.h>
 #include <stdbool.h>
 
-#include "target.h"
+#include "platform.h"
 
 typedef enum BlackboxDevice {
     BLACKBOX_DEVICE_SERIAL = 0,

src/main/common/encoding.c

@@ -0,0 +1,31 @@
+#include "encoding.h"
+
+/**
+ * Cast the in-memory representation of the given float directly to an int.
+ *
+ * This is useful for printing the hex representation of a float number (which is considerably cheaper
+ * than a full decimal float formatter, in both code size and output length).
+ */
+uint32_t castFloatBytesToInt(float f)
+{
+    union floatConvert_t {
+        float f;
+        uint32_t u;
+    } floatConvert;
+
+    floatConvert.f = f;
+
+    return floatConvert.u;
+}
+
+/**
+ * ZigZag encoding maps all values of a signed integer into those of an unsigned integer in such
+ * a way that numbers of small absolute value correspond to small integers in the result.
+ *
+ * (Compared to just casting a signed to an unsigned which creates huge resulting numbers for
+ * small negative integers).
+ */
+uint32_t zigzagEncode(int32_t value)
+{
+    return (uint32_t)((value << 1) ^ (value >> 31));
+}

src/main/common/encoding.h

@@ -0,0 +1,23 @@
+/*
+ * This file is part of Cleanflight.
+ *
+ * Cleanflight 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 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Cleanflight 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 Cleanflight.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <stdint.h>
+
+uint32_t castFloatBytesToInt(float f);
+uint32_t zigzagEncode(int32_t value);

src/test/Makefile

@@ -53,6 +53,7 @@ TESTS = \
 	rc_controls_unittest \
 	ledstrip_unittest \
 	ws2811_unittest \
+	encoding_unittest \
 	lowpass_unittest
 
 # All Google Test headers.  Usually you shouldn't change this
@@ -130,6 +131,25 @@ battery_unittest : \
 	$(OBJECT_DIR)/gtest_main.a
 
 	$(CXX) $(CXX_FLAGS) -lpthread $^ -o $(OBJECT_DIR)/$@
+	
+$(OBJECT_DIR)/common/encoding.o : $(USER_DIR)/common/encoding.c $(USER_DIR)/common/encoding.h $(GTEST_HEADERS)
+	@mkdir -p $(dir $@)
+	$(CC) $(C_FLAGS) $(TEST_CFLAGS) -c $(USER_DIR)/common/encoding.c -o $@
+
+$(OBJECT_DIR)/encoding_unittest.o : \
+	$(TEST_DIR)/encoding_unittest.cc \
+	$(USER_DIR)/common/encoding.h \
+	$(GTEST_HEADERS)
+
+	@mkdir -p $(dir $@)
+	$(CXX) $(CXX_FLAGS) $(TEST_CFLAGS) -c $(TEST_DIR)/encoding_unittest.cc -o $@
+
+encoding_unittest : \
+	$(OBJECT_DIR)/common/encoding.o \
+	$(OBJECT_DIR)/encoding_unittest.o \
+	$(OBJECT_DIR)/gtest_main.a
+
+	$(CXX) $(CXX_FLAGS) -lpthread $^ -o $(OBJECT_DIR)/$@
 
 $(OBJECT_DIR)/flight/imu.o : \
 	$(USER_DIR)/flight/imu.c \

src/test/unit/encoding_unittest.cc

@@ -0,0 +1,84 @@
+/*
+ * This file is part of Cleanflight.
+ *
+ * Cleanflight 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 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Cleanflight 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 Cleanflight.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#include <stdint.h>
+
+extern "C" {
+    #include "common/encoding.h"
+}
+
+#include "unittest_macros.h"
+#include "gtest/gtest.h"
+
+typedef struct zigzagEncodingExpectation_t {
+    int32_t input;
+    uint32_t expected;
+} zigzagEncodingExpectation_t;
+
+typedef struct floatToIntEncodingExpectation_t {
+    float input;
+    uint32_t expected;
+} floatToIntEncodingExpectation_t;
+
+TEST(EncodingTest, ZigzagEncodingTest)
+{
+    // given
+    zigzagEncodingExpectation_t expectations[] = {
+        { 0, 0},
+        {-1, 1},
+        { 1, 2},
+        {-2, 3},
+        { 2, 4},
+
+        { 2147483646, 4294967292},
+        {-2147483647, 4294967293},
+        { 2147483647, 4294967294},
+        {-2147483648, 4294967295},
+    };
+    int expectationCount = sizeof(expectations) / sizeof(expectations[0]);
+
+    // expect
+
+    for (int i = 0; i < expectationCount; i++) {
+        zigzagEncodingExpectation_t *expectation = &expectations[i];
+
+        EXPECT_EQ(expectation->expected, zigzagEncode(expectation->input));
+    }
+}
+
+TEST(EncodingTest, FloatToIntEncodingTest)
+{
+    // given
+    floatToIntEncodingExpectation_t expectations[] = {
+        {0.0, 0x00000000},
+        {2.0, 0x40000000}, // Exponent should be in the top bits
+        {4.5, 0x40900000}
+    };
+    int expectationCount = sizeof(expectations) / sizeof(expectations[0]);
+
+    // expect
+
+    for (int i = 0; i < expectationCount; i++) {
+        floatToIntEncodingExpectation_t *expectation = &expectations[i];
+
+        EXPECT_EQ(expectation->expected, castFloatBytesToInt(expectation->input));
+    }
+}
+
+// STUBS
+
+extern "C" {
+}