8.14 NEON scalars

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, x, into a doubleword vector, so that Dm[x] is the xth element in vector Dm. 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 x in the range 0-3.

  • 32-bit scalars are restricted to registers D0-D15, with x either 0 or 1.

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