function xperm8_lookup (idx, lut) = { let shamt : bits( 8) = (X(rs2)[31..0] >> shamt)[7..0]; let x : bits(32) = aes_mixcolumn_inv(X(rs1)[63..32]); X(rd) = EXTS((X(rs1) << 23) ^ ((x & 0x000000FE) << 7) ^