Difference between revisions of "Embedded Programming Tips and Tricks"

Revision as of 22:36, 12 November 2011

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 other, more complex, 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.

@@ Line 1: / Line 1: @@
 ===Fast Division===
-On microcontrollers without a divide instruction very fast division can be done by bit shifting a variable right.
+On microcontrollers without a divide instruction very fast division can be done by bit shifting a variable right.<br>
-Each shift does a divide by two.
+Each shift does a divide by two.<br>
-For example
+For example<br>
-Y = Y >> 1  Will result in a divide by 2
+Y = Y >> 1  Will result in a divide by 2<br>
-or
+or<br>
-X = X >> 4  Will result in a divide by 16
+X = X >> 4  Will result in a divide by 16<br>
-By adding a multiplication you can achieve other, more complex, divisions.
+By adding a multiplication you can achieve other, more complex, divisions.<br>
-For example
+For example<br>
-Z = Z * 3;
+Z = Z * 3;<br>
-Z = Z >> 4;  (div 16)
+Z = Z >> 4;  (div 16)<br>
-Will result in a division of 5.33 (16/3 = 5.33)
+Will result in a division of 5.33 (16/3 = 5.33)<br>
-Be sure to do the multiply first, otherwise bits will be lost.
+Be sure to do the multiply first, otherwise bits will be lost.<br>
-Also be sure the variable size is large enough to store the multiplied value.
+Also be sure the variable size is large enough to store the multiplied value.<br>