Handle subnormal numbers in float serialization

Author: vedderb

buffer.c

@@ -94,6 +94,12 @@ void buffer_append_float32(uint8_t* buffer, float number, float scale, int32_t *
  * floating point numbers in a fully defined manner.
  */
 void buffer_append_float32_auto(uint8_t* buffer, float number, int32_t *index) {
+	// Set subnormal numbers to 0 as they are not handled properly
+	// using this method.
+	if (fabsf(number) < 1.5e-38) {
+		number = 0.0;
+	}
+
 	int e = 0;
 	float sig = frexpf(number, &e);
 	float sig_abs = fabsf(sig);

tests/float_serialization/Makefile

@@ -0,0 +1,32 @@
+TARGET = test
+LIBS = -lm
+CC = gcc
+CFLAGS = -O2 -g -Wall -Wextra -Wundef -std=gnu99 -I../../ -DNO_STM32
+SOURCES = main.c ../../buffer.c
+HEADERS = ../../buffer.h
+OBJECTS = $(notdir $(SOURCES:.c=.o))
+
+.PHONY: default all clean
+
+default: $(TARGET)
+all: default
+
+%.o: %.c $(HEADERS)
+	$(CC) $(CFLAGS) -c $< -o $@
+	
+%.o: ../../%.c $(HEADERS)
+	$(CC) $(CFLAGS) -c $< -o $@
+
+.PRECIOUS: $(TARGET) $(OBJECTS)
+
+$(TARGET): $(OBJECTS)
+	$(CC) $(OBJECTS) -Wall $(LIBS) -o $@
+
+clean:
+	rm -f $(OBJECTS) $(TARGET)
+	
+test2:
+	echo $(OBJECTS)
+
+run: $(TARGET)
+	./$(TARGET)

tests/float_serialization/main.c

@@ -0,0 +1,51 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <string.h>
+#include <math.h>
+
+#include "buffer.h"
+
+void test_read(unsigned char *data) {
+	int32_t ind = 0;
+	union {
+		float f;
+		uint32_t i;
+	} flt;
+	
+	float res = buffer_get_float32_auto(data, &ind);
+	printf("Read buffer: %g\r\n", res);
+	
+	ind = 0;
+	flt.i = buffer_get_uint32(data, &ind);
+	printf("Read typecast: %g\r\n", flt.f);
+}
+
+int main(void) {
+	unsigned char data[4];
+	int32_t ind = 0;
+	
+	float number = 0.5e-38;
+	
+	printf("Test with subnormal number: %g\r\n", number);
+	
+	union {
+		float f;
+		uint32_t i;
+	} flt;
+	
+	printf("=== Add using buffer ===\r\n");
+	buffer_append_float32_auto(data, number, &ind);
+	ind = 0;
+	
+	test_read(data);
+	
+	printf("=== Add using typecast ===\r\n");
+	flt.f = number;
+	ind = 0;
+	buffer_append_uint32(data, flt.i, &ind);
+	test_read(data);
+	
+	return 0;
+}
+