diff --git a/src/Makefile.am b/src/Makefile.am
index c006144..e608b4f 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -43,6 +43,7 @@ libdivecomputer_la_SOURCES = \
 	uwatec_memomouse.h uwatec_memomouse.c \
 	oceanic.h \
 	oceanic_atom2.h oceanic_atom2.c \
+	ringbuffer.h ringbuffer.c \
 	utils.h utils.c
 
 if OS_WIN32
diff --git a/src/ringbuffer.c b/src/ringbuffer.c
new file mode 100644
index 0000000..0ccec7c
--- /dev/null
+++ b/src/ringbuffer.c
@@ -0,0 +1,79 @@
+#include <assert.h>
+
+#include "ringbuffer.h"
+
+
+static unsigned int
+normalize (unsigned int a, unsigned int size)
+{
+	return a % size;
+}
+
+
+static unsigned int
+distance (unsigned int a, unsigned int b, unsigned int size)
+{
+	if (a <= b) {
+		return (b - a) % size;
+	} else {
+		return size - (a - b) % size;
+	}
+}
+
+
+static unsigned int
+increment (unsigned int a, unsigned int delta, unsigned int size)
+{
+	return (a + delta) % size;
+}
+
+
+static unsigned int
+decrement (unsigned int a, unsigned int delta, unsigned int size)
+{
+	if (delta <= a) {
+		return (a - delta) % size;
+	} else {
+		return size - (delta - a) % size;
+	}
+}
+
+
+unsigned int
+ringbuffer_normalize (unsigned int a, unsigned int begin, unsigned int end)
+{
+	assert (end >= begin);
+	assert (a >= begin);
+
+	return normalize (a, end - begin);
+}
+
+
+unsigned int
+ringbuffer_distance (unsigned int a, unsigned int b, unsigned int begin, unsigned int end)
+{
+	assert (end >= begin);
+	assert (a >= begin);
+
+	return distance (a, b, end - begin);
+}
+
+
+unsigned int
+ringbuffer_increment (unsigned int a, unsigned int delta, unsigned int begin, unsigned int end)
+{
+	assert (end >= begin);
+	assert (a >= begin);
+
+	return increment (a - begin, delta, end - begin) + begin;
+}
+
+
+unsigned int
+ringbuffer_decrement (unsigned int a, unsigned int delta, unsigned int begin, unsigned int end)
+{
+	assert (end >= begin);
+	assert (a >= begin);
+
+	return decrement (a - begin, delta, end - begin) + begin;
+}
diff --git a/src/ringbuffer.h b/src/ringbuffer.h
new file mode 100644
index 0000000..0c4a117
--- /dev/null
+++ b/src/ringbuffer.h
@@ -0,0 +1,23 @@
+#ifndef RINGBUFFER_H
+#define RINGBUFFER_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif /* __cplusplus */
+
+unsigned int
+ringbuffer_normalize (unsigned int a, unsigned int begin, unsigned int end);
+
+unsigned int
+ringbuffer_distance (unsigned int a, unsigned int b, unsigned int begin, unsigned int end);
+
+unsigned int
+ringbuffer_increment (unsigned int a, unsigned int delta, unsigned int begin, unsigned int end);
+
+unsigned int
+ringbuffer_decrement (unsigned int a, unsigned int delta, unsigned int begin, unsigned int end);
+
+#ifdef __cplusplus
+}
+#endif /* __cplusplus */
+#endif /* RINGBUFFER_H */
diff --git a/src/suunto_common.c b/src/suunto_common.c
index 136bb96..5a8de36 100644
--- a/src/suunto_common.c
+++ b/src/suunto_common.c
@@ -2,29 +2,8 @@
 #include <string.h>
 
 #include "suunto_common.h"
+#include "ringbuffer.h"
 
-#define SUBSTRACT(a, x, begin, end) substract (a - begin, x, end - begin) + begin
-#define DISTANCE(a, b, begin, end) distance (a, b, end - begin)
-
-static unsigned int
-substract (unsigned int a, unsigned int x, unsigned int size)
-{
-	if (x <= a) {
-		return (a - x) % size;
-	} else {
-		return size - (x - a) % size;
-	}
-}
-
-static unsigned int
-distance (unsigned int a, unsigned int b, unsigned int size)
-{
-	if (a <= b) {
-		return (b - a) % size;
-	} else {
-		return size - (a - b) % size;
-	}
-}
 
 int
 suunto_common_extract_dives (const unsigned char data[], unsigned int begin, unsigned int end, unsigned int eop, unsigned int peek, dive_callback_t callback, void *userdata)
@@ -49,9 +28,9 @@ suunto_common_extract_dives (const unsigned char data[], unsigned int begin, uns
 
 		// Check for an end of dive marker (of the next dive),
 		// to find the start of the current dive.
-		unsigned int peek = SUBSTRACT (current, peek, begin, end);
+		unsigned int peek = ringbuffer_decrement (current, peek, begin, end);
 		if (data[peek] == 0x80) {
-			unsigned int len = DISTANCE (current, previous, begin, end);
+			unsigned int len = ringbuffer_distance (current, previous, begin, end);
 			if (current + len > end) {
 				unsigned int a = end - current;
 				unsigned int b = (current + len) - end;
diff --git a/src/suunto_d9.c b/src/suunto_d9.c
index 0078363..50aa87c 100644
--- a/src/suunto_d9.c
+++ b/src/suunto_d9.c
@@ -5,6 +5,7 @@
 #include "suunto.h"
 #include "serial.h"
 #include "utils.h"
+#include "ringbuffer.h"
 
 #define MAXRETRIES 2
 
@@ -16,24 +17,13 @@
 	message ("%s:%d: %s\n", __FILE__, __LINE__, expr); \
 }
 
-#define DISTANCE(a,b) distance (a, b, SUUNTO_D9_MEMORY_SIZE - 0x019A - 2)
+#define DISTANCE(a,b) ringbuffer_distance (a, b, 0x019A, SUUNTO_D9_MEMORY_SIZE - 2)
 
 struct d9 {
 	struct serial *port;
 };
 
 
-static unsigned int
-distance (unsigned int a, unsigned int b, unsigned int size)
-{
-	if (a <= b) {
-		return (b - a) % size;
-	} else {
-		return size - (a - b) % size;
-	}
-}
-
-
 int
 suunto_d9_open (d9 **out, const char* name)
 {
diff --git a/src/suunto_vyper2.c b/src/suunto_vyper2.c
index 4047d39..c7dcad9 100644
--- a/src/suunto_vyper2.c
+++ b/src/suunto_vyper2.c
@@ -5,6 +5,7 @@
 #include "suunto.h"
 #include "serial.h"
 #include "utils.h"
+#include "ringbuffer.h"
 
 #define MAXRETRIES 2
 
@@ -16,24 +17,13 @@
 	message ("%s:%d: %s\n", __FILE__, __LINE__, expr); \
 }
 
-#define DISTANCE(a,b) distance (a, b, SUUNTO_VYPER2_MEMORY_SIZE - 0x019A - 2)
+#define DISTANCE(a,b) ringbuffer_distance (a, b, 0x019A, SUUNTO_VYPER2_MEMORY_SIZE - 2)
 
 struct vyper2 {
 	struct serial *port;
 };
 
 
-static unsigned int
-distance (unsigned int a, unsigned int b, unsigned int size)
-{
-	if (a <= b) {
-		return (b - a) % size;
-	} else {
-		return size - (a - b) % size;
-	}
-}
-
-
 int
 suunto_vyper2_open (vyper2 **out, const char* name)
 {
diff --git a/src/uwatec_aladin.c b/src/uwatec_aladin.c
index 7c9bf0b..aa08370 100644
--- a/src/uwatec_aladin.c
+++ b/src/uwatec_aladin.c
@@ -4,6 +4,7 @@
 #include "uwatec.h"
 #include "serial.h"
 #include "utils.h"
+#include "ringbuffer.h"
 
 #define WARNING(expr) \
 { \
@@ -15,24 +16,13 @@
 	rc == -1 ? UWATEC_ERROR_IO : UWATEC_ERROR_TIMEOUT \
 )
 
+#define DISTANCE(a,b) ringbuffer_distance (a, b, 0, 0x600)
+
 struct aladin {
 	struct serial *port;
 };
 
 
-#define DISTANCE(a,b) distance (a, b, 0x600)
-
-static unsigned int
-distance (unsigned int a, unsigned int b, unsigned int size)
-{
-	if (a <= b) {
-		return (b - a) % size;
-	} else {
-		return size - (a - b) % size;
-	}
-}
-
-
 int
 uwatec_aladin_open (aladin **out, const char* name)
 {