rev

Reverse Bytes (Thumb)

REV <Rd>, <Rm>

Reverses bytes (Endian swap).

Details

Reverses the byte order of a 32-bit word (equivalent to endian conversion). No condition flags are affected. This is a 32-bit Thumb instruction available in ARMv6 and later.

Pseudocode Operation

Rd[31:24] ← Rm[7:0]
Rd[23:16] ← Rm[15:8]
Rd[15:8] ← Rm[23:16]
Rd[7:0] ← Rm[31:24]

Example

REV r0, r2

Encoding

Binary Layout
111110101
001
Rn
1111
Rd
10
00
Rm
 
Format Thumb Misc
Opcode 0xFA90F080
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
0x06BF0F30 REV{<c>}{<q>} <Rd>, <Rm> A32 cond | 01101 | 0 | 11 | 1 | 1 | 1 | 1 | Rd | 1 | 1 | 1 | 1 | 0 | 011 | Rm
0xBA00 REV{<c>}{<q>} <Rd>, <Rm> T32 10111010 | 00 | Rm | Rd
0xFA90F080 REV{<c>}.W <Rd>, <Rm> T32 111110101 | 001 | Rn | 1111 | Rd | 10 | 00 | Rm

Description

Byte-Reverse Word reverses the byte order in a 32-bit register.

Operation

if ConditionPassed() then
    EncodingSpecificOperations();
    bits(32) result;
    result<31:24> = R[m]<7:0>;
    result<23:16> = R[m]<15:8>;
    result<15:8>  = R[m]<23:16>;
    result<7:0>   = R[m]<31:24>;
    R[d] = result;