A data processing apparatus comprises a processing circuit and instruction decoder. A bitfield manipulation instruction controls the processing apparatus to generate at least one result data element from corresponding first and second source data elements. Each result data element includes a portion corresponding to a bitfield of the corresponding first source data element. Bits of the result data element that are more significant than the inserted bitfield have a prefix value that is selected, based on a control value specified by the instruction, as one of a first prefix value having a zero value, a second prefix value having the value of a portion of the corresponding second source data element, and a third prefix value corresponding to a sign extension of the bitfield of the first source data element. Bitwise logical instructions are also described.