SUBPT Subtract checked pointer This instruction subtracts an optionally-shifted register value from a base address register value, and writes the result to the destination register. The optionally-shifted register value is treated as the offset. If the operation would have generated a result where the most significant 8 bits of the result register differ from the most significant 8 bits of the base register, then the result is modified such that it is likely to be non-canonical when used as an address. 1 1 0 1 1 0 1 0 0 0 0 0 0 1 SUBPT <Xd|SP>, <Xn|SP>, <Xm>{, LSL #<amount>} if !IsFeatureImplemented(FEAT_CPA) then UNDEFINED; constant integer d = UInt(Rd); constant integer n = UInt(Rn); constant integer m = UInt(Rm); constant integer shift = UInt(imm3); <Xd|SP> Is the 64-bit name of the general-purpose destination register or stack pointer, encoded in the "Rd" field. <Xn|SP> Is the 64-bit name of the first general-purpose source register or stack pointer, encoded in the "Rn" field. <Xm> Is the 64-bit name of the second general-purpose source register, encoded in the "Rm" field. <amount> Is the left shift amount, in the range 0 to 7, defaulting to 0, encoded in the "imm3" field. bits(64) result; constant bits(64) base = if n == 31 then SP[] else X[n, 64]; constant bits(64) offset = LSL(X[m, 64], shift); result = base - offset; result = PointerAddCheck(result, base); if d == 31 then SP[] = result; else X[d, 64] = result;