SUB (extended register) Subtract (extended register) This instruction subtracts a sign or zero-extended register value, followed by an optional left shift amount, from a register value, and writes the result to the destination register. The argument that is extended from the <Rm> register can be a byte, halfword, word, or doubleword. If PSTATE.DIT is 1: The execution time of this instruction is independent of: The values of the data supplied in any of its registers. The values of the NZCV flags. The response of this instruction to asynchronous exceptions does not vary based on: The values of the data supplied in any of its registers. The values of the NZCV flags. 1 0 0 1 0 1 1 0 0 1 0 SUB <Wd|WSP>, <Wn|WSP>, <Wm>{, <extend> {#<amount>}} 1 SUB <Xd|SP>, <Xn|SP>, <R><m>{, <extend> {#<amount>}} if imm3 IN {'101', '110', '111'} then UNDEFINED; constant integer d = UInt(Rd); constant integer n = UInt(Rn); constant integer m = UInt(Rm); constant integer shift = UInt(imm3); constant integer datasize = 32 << UInt(sf); constant ExtendType extend_type = DecodeRegExtend(option); <Wd|WSP> Is the 32-bit name of the destination general-purpose register or stack pointer, encoded in the "Rd" field. <Wn|WSP> Is the 32-bit name of the first source general-purpose register or stack pointer, encoded in the "Rn" field. <Wm> Is the 32-bit name of the second general-purpose source register, encoded in the "Rm" field. <extend> For the 32-bit variant: is the extension to be applied to the second source operand, option <extend> 000 UXTB 001 UXTH 010 LSL|UXTW 011 UXTX 100 SXTB 101 SXTH 110 SXTW 111 SXTX If "Rd" or "Rn" is '11111' (WSP) and "option" is '010' then LSL is preferred, but may be omitted when "imm3" is '000'. In all other cases <extend> is required and must be UXTW when "option" is '010'. <extend> For the 64-bit variant: is the extension to be applied to the second source operand, option <extend> 000 UXTB 001 UXTH 010 UXTW 011 LSL|UXTX 100 SXTB 101 SXTH 110 SXTW 111 SXTX If "Rd" or "Rn" is '11111' (SP) and "option" is '011' then LSL is preferred, but may be omitted when "imm3" is '000'. In all other cases <extend> is required and must be UXTX when "option" is '011'. <amount> Is the left shift amount to be applied after extension in the range 0 to 4, defaulting to 0, encoded in the "imm3" field. It must be absent when <extend> is absent, is required when <extend> is LSL, and is optional when <extend> is present but not LSL. <Xd|SP> Is the 64-bit name of the destination general-purpose register or stack pointer, encoded in the "Rd" field. <Xn|SP> Is the 64-bit name of the first source general-purpose register or stack pointer, encoded in the "Rn" field. <R> Is a width specifier, option <R> 00x W 010 W x11 X 10x W 110 W <m> Is the number [0-30] of the second general-purpose source register or the name ZR (31), encoded in the "Rm" field. constant bits(datasize) operand1 = if n == 31 then SP[]<datasize-1:0> else X[n, datasize]; constant bits(datasize) operand2 = NOT(ExtendReg(m, extend_type, shift, datasize)); bits(datasize) result; (result, -) = AddWithCarry(operand1, operand2, '1'); if d == 31 then SP[] = ZeroExtend(result, 64); else X[d, datasize] = result;