Analog Devices ADSP-BF53x Blackfin, Reference

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ADSP-BF53x/BF56x Blackfin Processor Programming Reference 14-23
Shift/Rotate Operations
The sign of the rotate magnitude determines the direction of the rotation.
• Positive rotate magnitudes produce Left rotations.
• Negative rotate magnitudes produce Right rotations.
Valid rotate magnitudes are –32 t31, zero included. The Rotate
instruction masks and ignores bits that are more significant than those
allowed. The distance is determined by the lower 6 bits (sign extended) of
the
shift_magnitude
.
Unlike shift operations, the Rotate instruction loses no bits of the source
register data. Instead, it rearranges them in a circular fashion. However,
the last bit rotated out of the register remains in the
CC
bit, and is not
returned to the register. Because rotates are performed all at once and not
one bit at a time, rotating one direction or another regardless of the rotate
magnitude produces no advantage. For instance, a rotate right by two bits
is no more efficient than a rotate left by 30 bits. Both methods produce
identical results in identical execution time.
The D-register versions of this instruction rotate all 32 bits. The Accumu-
lator versions rotate all 40 bits of those registers.
The D-register versions of this instruction do not implicitly modify the
src_reg
values. Optionally,
dest_reg
can be the same D-register as
src_reg
. Doing this explicitly modifies the source register.