Embedded Programming Tips and Tricks

Fast Division

On microcontrollers without a divide instruction very fast division can be done by bit shifting a variable right.
Each shift does a divide by two.

For example

 Y = Y >> 1;  (Will result in a divide by 2)

or

 X = X >> 4;  (Will result in a divide by 16)

By adding a multiplication you can achieve a limited number of extra divisions.

For example

 Z = Z * 3;

 Z = Z >> 4;  (div 16)

Will result in a division of 5.33 (16/3 = 5.33)

Be sure to do the multiply first, otherwise bits will be lost.
Also be sure the variable size is large enough to store the multiplied value.