REV

Reverse bytes

This instruction reverses the byte order in a register.

Encoding: Integer

31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
	1	0	1	1	0	1	0	1	1	0	0	0	0	0	0	0	0	0	0	1	x
sf		S									opcode2									opc		Rn					Rd

32-bit (sf == 0 && opc == 10)

REV <Wd>, <Wn>

64-bit (sf == 1 && opc == 11)

REV <Xd>, <Xn>

Decoding algorithm

if opc == '11' && sf == '0' then EndOfDecode(Decode_UNDEF);

constant integer d = UInt(Rd);
constant integer n = UInt(Rn);
constant integer datasize = 32 << UInt(sf);
constant integer container_size = 8 << UInt(opc);

Operation

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

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

X[d, datasize] = result;

Explanations

<Wd>: Is the 32-bit name of the general-purpose destination register, encoded in the "Rd" field.
<Wn>: Is the 32-bit name of the general-purpose source register, encoded in the "Rn" field.
<Xd>: Is the 64-bit name of the general-purpose destination register, encoded in the "Rd" field.
<Xn>: Is the 64-bit name of the general-purpose source register, encoded in the "Rn" field.

Operational Notes

If PSTATE.DIT is 1:

• The execution time of this instruction is independent of:
  • The values of the data supplied in any of its registers.
  • The values of the NZCV flags.
• The response of this instruction to asynchronous exceptions does not vary based on:
  • The values of the data supplied in any of its registers.
  • The values of the NZCV flags.