In Thumb state, the high registers, r8–r15, are not part of the standard register set. You can use special variants of the MOV instruction to transfer a value from a low register, in the range r0–r7, to a high register, and from a high register to a low register. The CMP instruction enables you to compare high register values with low register values. The ADD instruction enables you to add high register values to low register values. For more details, see the ARM Architecture Reference Manual.