rbit

Reverse Bits (Thumb)

RBIT <Rd>, <Rm>

Reverses bits in a 32-bit register.

Details

Reverse Bits: Reverses all 32 bits in Rm and writes the result to Rd. Each bit position i is moved to position 31-i. The condition flags are not affected. This instruction is available in Thumb state (T32) and A32.

Pseudocode Operation

for i = 0 to 31
  Rd[i] ← Rm[31-i]

Example

RBIT r0, r2

Encoding

Binary Layout
111110101
001
Rn
1111
Rd
10
10
Rm
 
Format Thumb Misc
Opcode 0xFA90F0A0
Extension A32 (Base)

Operands

  • Rd
    Destination general-purpose register
  • Rm
    Second source / offset general-purpose register

Reference (Arm AArch32 ISA)

Instruction Forms

Encoding Instruction ISA Bit pattern
0x06FF0F30 RBIT{<c>}{<q>} <Rd>, <Rm> A32 cond | 01101 | 1 | 11 | 1 | 1 | 1 | 1 | Rd | 1 | 1 | 1 | 1 | 0 | 011 | Rm
0xFA90F0A0 RBIT{<c>}{<q>} <Rd>, <Rm> T32 111110101 | 001 | Rn | 1111 | Rd | 10 | 10 | Rm

Description

Reverse Bits reverses the bit order in a 32-bit register.

Operation

if ConditionPassed() then
    EncodingSpecificOperations();
    bits(32) result;
    for i = 0 to 31
        result<31-i> = R[m]<i>;
    R[d] = result;