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REV

Reverse Bytes reverses the byte order in a register.

This instruction is used by the pseudo-instruction REV64.

313029282726252423222120191817161514131211109876543210
sf10110101100000000001xRnRd
opc

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

REV <Wd>, <Wn>

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

REV <Xd>, <Xn>

integer d = UInt(Rd);
integer n = UInt(Rn);

integer datasize = if sf == '1' then 64 else 32;

integer container_size;
case opc of
    when '00'
        Unreachable();
    when '01'
        container_size = 16;
    when '10'
        container_size = 32;
    when '11'
        if sf == '0' then UNDEFINED;
        container_size = 64;

Assembler Symbols

<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.

Operation

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

integer containers = datasize DIV container_size;
integer elements_per_container = container_size DIV 8;
integer index = 0;
integer rev_index;
for c = 0 to containers-1
    rev_index = index + ((elements_per_container - 1) * 8);
    for e = 0 to elements_per_container-1
        result<rev_index+7:rev_index> = operand<index+7:index>;
        index = index + 8;
        rev_index = rev_index - 8;

X[d] = result;

Operational information

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.
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