diff --git a/src/cochran_commander.c b/src/cochran_commander.c
index 2dbdc1b..83f8800 100644
--- a/src/cochran_commander.c
+++ b/src/cochran_commander.c
@@ -603,7 +603,7 @@ cochran_commander_profile_size(cochran_commander_device_t *device, cochran_data_
 		// Corrupt dive, guess the end address
 		sample_end_address = cochran_commander_guess_sample_end_address(device, data, dive_num);
 
-	return ringbuffer_distance(sample_start_address, sample_end_address, 0, device->layout->rb_profile_begin, device->layout->rb_profile_end);
+	return ringbuffer_distance(sample_start_address, sample_end_address, DC_RINGBUFFER_EMPTY, device->layout->rb_profile_begin, device->layout->rb_profile_end);
 }
 
 
diff --git a/src/cressi_edy.c b/src/cressi_edy.c
index 41a9397..c4e78c1 100644
--- a/src/cressi_edy.c
+++ b/src/cressi_edy.c
@@ -432,7 +432,7 @@ cressi_edy_device_foreach (dc_device_t *abstract, dc_dive_callback_t callback, v
 	}
 
 	// Get the number of logbook items.
-	unsigned int count = ringbuffer_distance (first, last, 0, layout->rb_logbook_begin, layout->rb_logbook_end) + 1;
+	unsigned int count = ringbuffer_distance (first, last, DC_RINGBUFFER_EMPTY, layout->rb_logbook_begin, layout->rb_logbook_end) + 1;
 
 	// Get the profile pointer.
 	unsigned int eop = array_uint_le (logbook + layout->config + 2, layout->rb_logbook_size) * SZ_PAGE + layout->rb_profile_begin;
@@ -457,7 +457,7 @@ cressi_edy_device_foreach (dc_device_t *abstract, dc_dive_callback_t callback, v
 		}
 
 		// Get the profile length.
-		unsigned int length = ringbuffer_distance (current, previous, 1, layout->rb_profile_begin, layout->rb_profile_end);
+		unsigned int length = ringbuffer_distance (current, previous, DC_RINGBUFFER_FULL, layout->rb_profile_begin, layout->rb_profile_end);
 
 		// Check for a ringbuffer overflow.
 		if (total + length > layout->rb_profile_end - layout->rb_profile_begin) {
@@ -510,7 +510,7 @@ cressi_edy_device_foreach (dc_device_t *abstract, dc_dive_callback_t callback, v
 		}
 
 		// Get the profile length.
-		unsigned int length = ringbuffer_distance (current, previous, 1, layout->rb_profile_begin, layout->rb_profile_end);
+		unsigned int length = ringbuffer_distance (current, previous, DC_RINGBUFFER_FULL, layout->rb_profile_begin, layout->rb_profile_end);
 
 		// Move to the begin of the current dive.
 		offset -= length;
diff --git a/src/cressi_leonardo.c b/src/cressi_leonardo.c
index dd941da..b1ec8b4 100644
--- a/src/cressi_leonardo.c
+++ b/src/cressi_leonardo.c
@@ -41,7 +41,7 @@
 
 #define RB_PROFILE_BEGIN 0x1438
 #define RB_PROFILE_END   SZ_MEMORY
-#define RB_PROFILE_DISTANCE(a,b) ringbuffer_distance (a, b, 0, RB_PROFILE_BEGIN, RB_PROFILE_END)
+#define RB_PROFILE_DISTANCE(a,b) ringbuffer_distance (a, b, DC_RINGBUFFER_EMPTY, RB_PROFILE_BEGIN, RB_PROFILE_END)
 
 #define MAXRETRIES 4
 #define PACKETSIZE 32
diff --git a/src/hw_frog.c b/src/hw_frog.c
index f98523b..2de4eba 100644
--- a/src/hw_frog.c
+++ b/src/hw_frog.c
@@ -40,7 +40,7 @@
 
 #define RB_PROFILE_BEGIN 0x000000
 #define RB_PROFILE_END   0x200000
-#define RB_PROFILE_DISTANCE(a,b) ringbuffer_distance (a, b, 0, RB_PROFILE_BEGIN, RB_PROFILE_END)
+#define RB_PROFILE_DISTANCE(a,b) ringbuffer_distance (a, b, DC_RINGBUFFER_EMPTY, RB_PROFILE_BEGIN, RB_PROFILE_END)
 
 #define READY      0x4D
 #define HEADER     0x61
diff --git a/src/liquivision_lynx.c b/src/liquivision_lynx.c
index 51423b6..3ce8743 100644
--- a/src/liquivision_lynx.c
+++ b/src/liquivision_lynx.c
@@ -67,12 +67,12 @@
 #define RB_LOGBOOK_BEGIN         (1 * PAGESIZE)
 #define RB_LOGBOOK_END           (25 * PAGESIZE)
 #define RB_LOGBOOK_SIZE          (RB_LOGBOOK_END - RB_LOGBOOK_BEGIN)
-#define RB_LOGBOOK_DISTANCE(a,b) ringbuffer_distance (a, b, 1, RB_LOGBOOK_BEGIN, RB_LOGBOOK_END)
+#define RB_LOGBOOK_DISTANCE(a,b) ringbuffer_distance (a, b, DC_RINGBUFFER_FULL, RB_LOGBOOK_BEGIN, RB_LOGBOOK_END)
 
 #define RB_PROFILE_BEGIN         (25 * PAGESIZE)
 #define RB_PROFILE_END           (500 * PAGESIZE)
 #define RB_PROFILE_SIZE          (RB_PROFILE_END - RB_PROFILE_BEGIN)
-#define RB_PROFILE_DISTANCE(a,b) ringbuffer_distance (a, b, 1, RB_PROFILE_BEGIN, RB_PROFILE_END)
+#define RB_PROFILE_DISTANCE(a,b) ringbuffer_distance (a, b, DC_RINGBUFFER_FULL, RB_PROFILE_BEGIN, RB_PROFILE_END)
 
 #define SZ_HEADER_XEN   80
 #define SZ_HEADER_OTHER 96
diff --git a/src/oceanic_common.c b/src/oceanic_common.c
index e9b3d32..55dfebe 100644
--- a/src/oceanic_common.c
+++ b/src/oceanic_common.c
@@ -32,10 +32,10 @@
 
 #define VTABLE(abstract)	((const oceanic_common_device_vtable_t *) abstract->vtable)
 
-#define RB_LOGBOOK_DISTANCE(a,b,l)	ringbuffer_distance (a, b, 1, l->rb_logbook_begin, l->rb_logbook_end)
+#define RB_LOGBOOK_DISTANCE(a,b,l)	ringbuffer_distance (a, b, DC_RINGBUFFER_FULL, l->rb_logbook_begin, l->rb_logbook_end)
 #define RB_LOGBOOK_INCR(a,b,l)		ringbuffer_increment (a, b, l->rb_logbook_begin, l->rb_logbook_end)
 
-#define RB_PROFILE_DISTANCE(a,b,l)	ringbuffer_distance (a, b, 0, l->rb_profile_begin, l->rb_profile_end)
+#define RB_PROFILE_DISTANCE(a,b,l)	ringbuffer_distance (a, b, DC_RINGBUFFER_EMPTY, l->rb_profile_begin, l->rb_profile_end)
 #define RB_PROFILE_INCR(a,b,l)		ringbuffer_increment (a, b, l->rb_profile_begin, l->rb_profile_end)
 
 #define INVALID 0
diff --git a/src/ringbuffer.c b/src/ringbuffer.c
index 72318d0..bea496d 100644
--- a/src/ringbuffer.c
+++ b/src/ringbuffer.c
@@ -25,39 +25,43 @@
 
 
 static unsigned int
-normalize (unsigned int a, unsigned int size)
+modulo (unsigned int x, unsigned int n, unsigned int d)
 {
-	return a % size;
-}
-
-
-static unsigned int
-distance (unsigned int a, unsigned int b, int mode, unsigned int size)
-{
-	if (a < b) {
-		return (b - a) % size;
-	} else if (a > b) {
-		return size - (a - b) % size;
+	unsigned int result = 0;
+	if (d > x) {
+#if 0
+		result = (n - (d - x) % n) % n;
+#else
+		unsigned int m = (d - x) % n;
+		result = m ? n - m : m;
+#endif
 	} else {
-		return (mode == 0 ? 0 : size);
+		result = (x - d) % n;
 	}
+
+	return result + d;
 }
 
 
 static unsigned int
-increment (unsigned int a, unsigned int delta, unsigned int size)
+distance (unsigned int a, unsigned int b, unsigned int n, unsigned int mode)
 {
-	return (a + delta) % size;
-}
-
-
-static unsigned int
-decrement (unsigned int a, unsigned int delta, unsigned int size)
-{
-	if (delta <= a) {
-		return (a - delta) % size;
+	unsigned int result = 0;
+	if (a > b) {
+#if 0
+		result = (n - (a - b) % n) % n;
+#else
+		unsigned int m = (a - b) % n;
+		result = m ? n - m : m;
+#endif
 	} else {
-		return size - (delta - a) % size;
+		result = (b - a) % n;
+	}
+
+	if (result == 0) {
+		return (mode == 0 ? 0 : n);
+	} else {
+		return result;
 	}
 }
 
@@ -65,38 +69,38 @@ decrement (unsigned int a, unsigned int delta, unsigned int size)
 unsigned int
 ringbuffer_normalize (unsigned int a, unsigned int begin, unsigned int end)
 {
-	assert (end >= begin);
-	assert (a >= begin);
+	assert (end > begin);
 
-	return normalize (a, end - begin);
+	unsigned int n = end - begin;
+	return modulo (a, n, begin);
 }
 
 
 unsigned int
 ringbuffer_distance (unsigned int a, unsigned int b, int mode, unsigned int begin, unsigned int end)
 {
-	assert (end >= begin);
-	assert (a >= begin);
+	assert (end > begin);
 
-	return distance (a, b, mode, end - begin);
+	unsigned int n = end - begin;
+	return distance (a, b, n, mode);
 }
 
 
 unsigned int
 ringbuffer_increment (unsigned int a, unsigned int delta, unsigned int begin, unsigned int end)
 {
-	assert (end >= begin);
-	assert (a >= begin);
+	assert (end > begin);
 
-	return increment (a - begin, delta, end - begin) + begin;
+	unsigned int n = end - begin;
+	return modulo (a + delta % n, n, begin);
 }
 
 
 unsigned int
 ringbuffer_decrement (unsigned int a, unsigned int delta, unsigned int begin, unsigned int end)
 {
-	assert (end >= begin);
-	assert (a >= begin);
+	assert (end > begin);
 
-	return decrement (a - begin, delta, end - begin) + begin;
+	unsigned int n = end - begin;
+	return modulo (a + n - delta % n, n, begin);
 }
diff --git a/src/ringbuffer.h b/src/ringbuffer.h
index 3915739..e41cd5a 100644
--- a/src/ringbuffer.h
+++ b/src/ringbuffer.h
@@ -26,6 +26,9 @@
 extern "C" {
 #endif /* __cplusplus */
 
+#define DC_RINGBUFFER_EMPTY 0
+#define DC_RINGBUFFER_FULL  1
+
 unsigned int
 ringbuffer_normalize (unsigned int a, unsigned int begin, unsigned int end);
 
diff --git a/src/seac_screen.c b/src/seac_screen.c
index 5c566aa..3015fd6 100644
--- a/src/seac_screen.c
+++ b/src/seac_screen.c
@@ -58,7 +58,7 @@
 #define RB_PROFILE_BEGIN         0x010000
 #define RB_PROFILE_END           0x200000
 #define RB_PROFILE_SIZE          (RB_PROFILE_END - RB_PROFILE_BEGIN)
-#define RB_PROFILE_DISTANCE(a,b) ringbuffer_distance (a, b, 1, RB_PROFILE_BEGIN, RB_PROFILE_END)
+#define RB_PROFILE_DISTANCE(a,b) ringbuffer_distance (a, b, DC_RINGBUFFER_FULL, RB_PROFILE_BEGIN, RB_PROFILE_END)
 #define RB_PROFILE_INCR(a,d)     ringbuffer_increment (a, d, RB_PROFILE_BEGIN, RB_PROFILE_END)
 
 typedef struct seac_screen_device_t {
diff --git a/src/suunto_common.c b/src/suunto_common.c
index 9988b86..080b530 100644
--- a/src/suunto_common.c
+++ b/src/suunto_common.c
@@ -27,7 +27,7 @@
 #include "ringbuffer.h"
 #include "array.h"
 
-#define RB_PROFILE_DISTANCE(a,b,l)	ringbuffer_distance (a, b, 0, l->rb_profile_begin, l->rb_profile_end)
+#define RB_PROFILE_DISTANCE(a,b,l)	ringbuffer_distance (a, b, DC_RINGBUFFER_EMPTY, l->rb_profile_begin, l->rb_profile_end)
 #define RB_PROFILE_PEEK(a,l)		ringbuffer_decrement (a, l->peek, l->rb_profile_begin, l->rb_profile_end)
 
 void
diff --git a/src/suunto_common2.c b/src/suunto_common2.c
index d33f725..c26eb54 100644
--- a/src/suunto_common2.c
+++ b/src/suunto_common2.c
@@ -297,7 +297,7 @@ suunto_common2_device_foreach (dc_device_t *abstract, dc_dive_callback_t callbac
 		ERROR (abstract->context, "Invalid ringbuffer pointer detected (0x%04x 0x%04x 0x%04x %u).", begin, last, end, count);
 		remaining = layout->rb_profile_end - layout->rb_profile_begin;
 	} else {
-		remaining = RB_PROFILE_DISTANCE (layout, begin, end, count != 0);
+		remaining = RB_PROFILE_DISTANCE (layout, begin, end, count ? DC_RINGBUFFER_FULL : DC_RINGBUFFER_EMPTY);
 	}
 
 	// Update and emit a progress event.
@@ -328,7 +328,7 @@ suunto_common2_device_foreach (dc_device_t *abstract, dc_dive_callback_t callbac
 	unsigned int offset = remaining;
 	while (offset) {
 		// Calculate the size of the current dive.
-		unsigned int size = RB_PROFILE_DISTANCE (layout, current, previous, 1);
+		unsigned int size = RB_PROFILE_DISTANCE (layout, current, previous, DC_RINGBUFFER_FULL);
 
 		if (size < 4 || size > offset) {
 			ERROR (abstract->context, "Unexpected profile size (%u %u).", size, offset);
diff --git a/src/suunto_solution.c b/src/suunto_solution.c
index e72fe94..e3e6b1c 100644
--- a/src/suunto_solution.c
+++ b/src/suunto_solution.c
@@ -300,7 +300,7 @@ suunto_solution_extract_dives (dc_device_t *abstract, const unsigned char data[]
 		// to find the start of the current dive.
 		unsigned int peek = ringbuffer_increment (current, 2, RB_PROFILE_BEGIN, RB_PROFILE_END);
 		if (data[peek] == 0x80) {
-			unsigned int len = ringbuffer_distance (previous, current, 0, RB_PROFILE_BEGIN, RB_PROFILE_END);
+			unsigned int len = ringbuffer_distance (previous, current, DC_RINGBUFFER_EMPTY, RB_PROFILE_BEGIN, RB_PROFILE_END);
 
 			if (callback && !callback (buffer + idx, len, NULL, 0, userdata))
 				return DC_STATUS_SUCCESS;
diff --git a/src/uwatec_aladin.c b/src/uwatec_aladin.c
index 1cfec54..ee15433 100644
--- a/src/uwatec_aladin.c
+++ b/src/uwatec_aladin.c
@@ -36,7 +36,7 @@
 #define RB_PROFILE_BEGIN			0x000
 #define RB_PROFILE_END				0x600
 #define RB_PROFILE_NEXT(a)			ringbuffer_increment (a, 1, RB_PROFILE_BEGIN, RB_PROFILE_END)
-#define RB_PROFILE_DISTANCE(a,b)	ringbuffer_distance (a, b, 0, RB_PROFILE_BEGIN, RB_PROFILE_END)
+#define RB_PROFILE_DISTANCE(a,b)	ringbuffer_distance (a, b, DC_RINGBUFFER_EMPTY, RB_PROFILE_BEGIN, RB_PROFILE_END)
 
 #define HEADER 4
 
diff --git a/src/zeagle_n2ition3.c b/src/zeagle_n2ition3.c
index 53ac363..0d43122 100644
--- a/src/zeagle_n2ition3.c
+++ b/src/zeagle_n2ition3.c
@@ -277,7 +277,7 @@ zeagle_n2ition3_device_foreach (dc_device_t *abstract, dc_dive_callback_t callba
 	}
 
 	// Get the number of logbook items.
-	unsigned int count = ringbuffer_distance (first, last, 0, RB_LOGBOOK_BEGIN, RB_LOGBOOK_END) + 1;
+	unsigned int count = ringbuffer_distance (first, last, DC_RINGBUFFER_EMPTY, RB_LOGBOOK_BEGIN, RB_LOGBOOK_END) + 1;
 
 	// Get the profile pointer.
 	unsigned int eop = array_uint16_le (config + 0x7E);
@@ -302,7 +302,7 @@ zeagle_n2ition3_device_foreach (dc_device_t *abstract, dc_dive_callback_t callba
 		}
 
 		// Get the profile length.
-		unsigned int length = ringbuffer_distance (current, previous, 1, RB_PROFILE_BEGIN, RB_PROFILE_END);
+		unsigned int length = ringbuffer_distance (current, previous, DC_RINGBUFFER_FULL, RB_PROFILE_BEGIN, RB_PROFILE_END);
 
 		// Check for a ringbuffer overflow.
 		if (total + length > RB_PROFILE_END - RB_PROFILE_BEGIN) {
@@ -344,7 +344,7 @@ zeagle_n2ition3_device_foreach (dc_device_t *abstract, dc_dive_callback_t callba
 		unsigned int current = array_uint16_le (config + 2 * idx);
 
 		// Get the profile length.
-		unsigned int length = ringbuffer_distance (current, previous, 1, RB_PROFILE_BEGIN, RB_PROFILE_END);
+		unsigned int length = ringbuffer_distance (current, previous, DC_RINGBUFFER_FULL, RB_PROFILE_BEGIN, RB_PROFILE_END);
 
 		// Move to the begin of the current dive.
 		offset -= length;