2.21 Access to the inline barrel shifter

The ARM arithmetic logic unit has a 32-bit barrel shifter that is capable of shift and rotate operations.

The second operand to many ARM and Thumb data-processing and single register data-transfer instructions can be shifted, before the data-processing or data-transfer is executed, as part of the instruction. This supports, but is not limited to:

  • Scaled addressing.

  • Multiplication by an immediate value.

  • Constructing immediate values.

32-bit Thumb instructions give almost the same access to the barrel shifter as ARM instructions.

The 16-bit Thumb instructions only allow access to the barrel shifter using separate instructions.

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