Some NEON instructions act on scalars in combination with
vectors. NEON scalars can be 8-bit, 16-bit, 32-bit, or 64-bit. The
instruction syntax refers to the scalars using an index,
into a doubleword vector, so that
xth element in vector
Other than multiply instructions, instructions that access scalars
can access any element in the register bank.
Multiply instructions only allow 16-bit or 32-bit scalars, and can only access the first 32 scalars in the register bank. That is, in multiply instructions:
16-bit scalars are restricted to registers D0-D7, with
in the range 0-3
32-bit scalars are restricted to registers D0-D15, with
either 0 or 1.