rev16

Reverse Bytes in Halfwords

REV16 <Wd>, <Wn>

Reverses bytes in each 16-bit halfword.

Pseudocode Operation

result[7:0] ← Wn[15:8]
result[15:8] ← Wn[7:0]
result[23:16] ← Wn[31:24]
result[31:24] ← Wn[23:16]
Wd ← result

Example

REV16 w0, w1

Encoding

Binary Layout

0

31

1

30

0

29

11010110

28:21

00000

20:16

0000

15:12

01

11:10

Rn

9:5

Rd

4:0

 

Format Data Processing

Opcode 0x5AC00400

Extension Base

Operands

• Wd
  Destination 32-bit integer register
• Wn
  First source / base 32-bit integer register

Related

Other forms of rev16

• rev16 Reverse Bytes Halfword (Thumb)
• rev16 Reverse Bytes in Halfwords (Thumb)

Across architectures

Byte Swap (Endianness Reversal) : how x86, ARM, RISC-V, and PowerISA each do this.

More in Base

Reference

View in Arm A64 ISA Reference ↗ Arm A64 ISA

Instruction Forms

Encoding	Instruction		ISA		Bit pattern
0x0E201800	REV16 <Vd>.<T>, <Vn>.<T>		A64		0 | Q | 0 | 01110 | size | 100000000 | 1 | 10 | Rn | Rd
0x5AC00400	REV16 <Wd>, <Wn>		A64		0 | 1 | 0 | 11010110 | 00000 | 0000 | 01 | Rn | Rd
0xDAC00400	REV16 <Xd>, <Xn>		A64		1 | 1 | 0 | 11010110 | 00000 | 0000 | 01 | Rn | Rd

Description

Reverse bytes in 16-bit halfwords reverses the byte order in each 16-bit halfword of a register.

Operation

bits(datasize) operand = X[n, datasize];
bits(datasize) result;

constant integer containers = datasize DIV container_size;
for c = 0 to containers-1
    bits(container_size) container = Elem[operand, c, container_size];
    Elem[result, c, container_size] = Reverse(container, 8);

X[d, datasize] = result;