rev8
Byte-reverse register (RV64 encoding)
This instruction is defined by:
-
anyOf:
-
B, version >= 0
-
Zbb, version >= 0
-
Zbkb, version >= 0
-
This instruction is included in the following profiles:
-
RVA22S64 (Mandatory)
-
RVA22U64 (Mandatory)
Synopsis
| This instruction must have data-independent timing when extension Zkt is enabled. |
This instruction reverses the order of the bytes in rs1.
| The rev8 mnemonic corresponds to different instruction encodings in RV32 and RV64. |
The byte-reverse operation is only available for the full register width. To emulate word-sized
and halfword-sized byte-reversal, perform a rev8 rd,rs followed by a srai rd,rd,K, where K
is XLEN-32 and XLEN-16, respectively.
|
Decode Variables
-
RV32
-
RV64
Bits<5> rs1 = $encoding[19:15];
Bits<5> rd = $encoding[11:7];Bits<5> rs1 = $encoding[19:15];
Bits<5> rd = $encoding[11:7];Execution
-
IDL
-
Sail
if (implemented?(ExtensionName::B) && (CSR[misa].B == 1'b0)) {
raise(ExceptionCode::IllegalInstruction, mode(), $encoding);
}
XReg input = X[rs1];
XReg output = 0;
XReg j = xlen() - 1;
for (U32 i = 0; i < (xlen() - 8); i = i + 8) {
output[(i + 7):i] = input[j:(j - 7)];
j = j - 8;
}
X[rd] = output;{
let rs1_val = X(rs1);
result : xlenbits = zeros();
foreach (i from 0 to (sizeof(xlen) - 8) by 8)
result[(i + 7) .. i] = rs1_val[(sizeof(xlen) - i - 1) .. (sizeof(xlen) - i - 8)];
X(rd) = result;
RETIRE_SUCCESS
}