In aarch64, the bitwise operation immediates are a bit more complicated. From the documentation Is the bitmask immediate. Such an immediate is a 32-bit or 64-b

In aarch64, the bitwise operation immediates are a bit more complicated. From the documentation Is the bitmask immediate. Such an immediate is a 32-bit or 64-bit pattern viewed as a vector of identical elements of size e = 2, 4, 8, 16, 32, or 64 bits. Each element contains the same sub-pattern: a single run of 1 to e-1 non-zero bits, rotated by 0 to e-1 bits. This mechanism can generate 5,334 unique 64-bit patterns (as 2,667 pairs of pattern and their bitwise inverse). Because the all-zeros and all-ones values cannot be described in this way, the assembler generates an error message. http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0802b/AND_log_imm.html http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.... I feel like I have a vague memory of a single byte being repeated with some specific pattern for some instruction, but I can't find it anymore.