Performing Rotations in C

The C language has operators to perform left and right bitwise shift operations (« and »), but it does not have a rotate operator. When rotating, any bit shifted out of the value is shifted back into the now empty bit location.

Simple expressions can be used to obtain a rotated value, however. For example, to rotate an 8-bit wide unsigned variable, c, one bit to the left, the following code can be used:

c = (c << 1) | (c >> 7);
To rotate a 16-bit wide unsigned variable, i, 2 bits to the right, you could use:
i =  (i >> 2) | (i << 14);
From these expressions you can see that rotating a byte one bit to the left, for example, is the same as rotating it 7 bits to the right. And here’s a bonus of using statements such as those above: If you are using the MPLAB® XC8 compiler, it will detect that these operations perform a rotation and will use the 8-bit PIC® MCU device’s rotate instruction when possible.
© 2017 Microchip Technology, Inc.
Information contained on this site regarding device applications and the like is provided only for your convenience and may be superseded by updates. It is your responsibility to ensure that your application meets with your specifications. MICROCHIP MAKES NO REPRESENTATIONS OR WARRANTIES OF ANY KIND WHETHER EXPRESS OR IMPLIED, WRITTEN OR ORAL, STATUTORY OR OTHERWISE, RELATED TO THE INFORMATION, INCLUDING BUT NOT LIMITED TO ITS CONDITION, QUALITY, PERFORMANCE, MERCHANTABILITY OR FITNESS FOR PURPOSE. Microchip disclaims all liability arising from this information and its use. Use of Microchip devices in life support and/or safety applications is entirely at the buyer's risk, and the buyer agrees to defend, indemnify and hold harmless Microchip from any and all damages, claims, suits, or expenses resulting from such use. No licenses are conveyed, implicitly or otherwise, under any Microchip intellectual property rights.