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RRX

Rotate Right with Extend. This instruction is a preferred synonym for MOV instructions with shifted register operands.

Syntax

RRX{S}{cond} Rd, Rm

where:

S

is an optional suffix. If S is specified, the condition flags are updated on the result of the operation.

Rd

is the destination register.

Rm

is the register holding the first operand. This operand is shifted right.

Operation

RRX provides the value of the contents of a register shifted right one bit. The old carry flag is shifted into bit[31]. If the S suffix is present, the old bit[0] is placed in the carry flag.

Restrictions in T32 code

T32 instructions must not use PC or SP.

Use of SP and PC in A32 instructions

You can use SP in this A32 instruction but this is deprecated.

If you use PC as Rm, the value used is the address of the instruction plus 8.

If you use PC as Rd:

  • Execution branches to the address corresponding to the result.
  • If you use the S suffix, the SPSR of the current mode is copied to the CPSR. You can use this to return from exceptions.

    Note

    The A32 instruction RRXS{cond} pc,Rm always disassembles to the preferred form MOVS{cond} pc,Rm{,shift}.

Do not use the S suffix when using PC as Rd in User mode or System mode. The assembler cannot warn you about this because it has no information about what the processor mode is likely to be at execution time.

You cannot use PC for Rd or any operand in this instruction if it has a register-controlled shift.

Condition flags

If S is specified, the instruction updates the N and Z flags according to the result.

The C flag is unaffected if the shift value is 0. Otherwise, the C flag is updated to the last bit shifted out.

Architectures

The 32-bit instruction is available in A32 and T32.

There is no 16-bit instruction in T32.

Related reference
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