diff --git a/Makefile b/Makefile
index 5391157..d33ccf2 100644
--- a/Makefile
+++ b/Makefile
@@ -80,7 +80,7 @@ PROGID = arduino
 
 PROGRAM = mendel
 
-SOURCES = $(PROGRAM).c dda.c gcode_parse.c gcode_process.c timer.c temp.c sermsg.c dda_queue.c watchdog.c debug.c sersendf.c heater.c analog.c intercom.c pinio.c clock.c home.c crc.c delay.c
+SOURCES = $(PROGRAM).c gcode_parse.c gcode_process.c dda.c dda_maths.c dda_queue.c timer.c temp.c sermsg.c watchdog.c debug.c sersendf.c heater.c analog.c intercom.c pinio.c clock.c home.c crc.c delay.c
 
 ARCH = avr-
 CC = $(ARCH)gcc
diff --git a/dda_maths.c b/dda_maths.c
new file mode 100644
index 0000000..1c6d8db
--- /dev/null
+++ b/dda_maths.c
@@ -0,0 +1,60 @@
+
+/** \file
+	\brief Mathematic algorithms for the digital differential analyser (DDA).
+*/
+
+#include "dda_maths.h"
+
+#include <stdlib.h>
+#include <stdint.h>
+
+/*!
+  Integer multiply-divide algorithm.
+
+  \param multiplicand
+  \param multiplier
+  \param divisor
+  \return rounded result of multiplicand * multiplier / divisor
+
+  Calculate a * b / c, without overflowing and without using 64-bit integers.
+  Doing this the standard way, a * b could easily overflow, even if the correct
+  overall result fits into 32 bits. This algorithm avoids this intermediate
+  overflow and delivers valid results for all cases where each of the three
+  operators as well as the result fits into 32 bits.
+
+  Found on  http://stackoverflow.com/questions/4144232/
+  how-to-calculate-a-times-b-divided-by-c-only-using-32-bit-integer-types-even-i
+*/
+const uint32_t muldiv(uint32_t multiplicand, uint32_t multiplier,
+                      uint32_t divisor) {
+  uint32_t quotient = 0;
+  uint32_t remainder = 0;
+  uint32_t qn = multiplier / divisor;
+  uint32_t rn = multiplier % divisor;
+
+  while(multiplicand) {
+    if (multiplicand & 1) {
+      quotient += qn;
+      remainder += rn;
+      if (remainder >= divisor) {
+        quotient++;
+        remainder -= divisor;
+      }
+    }
+    multiplicand  >>= 1;
+    qn <<= 1;
+    rn <<= 1;
+    if (rn >= divisor) {
+      qn++; 
+      rn -= divisor;
+    }
+  }
+
+  // rounding
+  if (remainder > divisor / 2)
+    quotient++;
+
+  // remainder is valid here, but not returned
+  return quotient;
+}
+
diff --git a/dda_maths.h b/dda_maths.h
new file mode 100644
index 0000000..9efcf7a
--- /dev/null
+++ b/dda_maths.h
@@ -0,0 +1,11 @@
+#ifndef	_DDA_MATHS_H
+#define	_DDA_MATHS_H
+
+#include	<stdint.h>
+
+
+// return rounded result of multiplicand * multiplier / divisor
+const uint32_t muldiv(uint32_t multiplicand, uint32_t multiplier,
+                      uint32_t divisor);
+
+#endif	/* _DDA_MATHS_H */