SUBS (shifted register) -- A64

This instruction subtracts an optionally-shifted register value from a register value, and writes the result to the destination register. It updates the condition flags based on the result.

Decode for all variants of this encoding

if shift == '11' then EndOfDecode(Decode_UNDEF); end; if sf == '0' && imm6[5] == '1' then EndOfDecode(Decode_UNDEF); end; let d : integer{} = UInt(Rd); let n : integer{} = UInt(Rn); let m : integer{} = UInt(Rm); let datasize : integer{} = 32 << UInt(sf); let shift_type : ShiftType = DecodeShift(shift); let shift_amount : integer = UInt(imm6);

Assembler Symbols

<Wd>	Is the 32-bit name of the general-purpose destination register, encoded in the "Rd" field.

<Wn>	Is the 32-bit name of the first general-purpose source register, encoded in the "Rn" field.

<Wm>	Is the 32-bit name of the second general-purpose source register, encoded in the "Rm" field.

<shift>

Is the optional shift type to be applied to the second source operand, defaulting to LSL and encoded in shift:

shift	<shift>
00	LSL
01	LSR
10	ASR
11	RESERVED

<amount>	For the "32-bit" variant: is the shift amount, in the range 0 to 31, defaulting to 0 and encoded in the "imm6" field.
	For the "64-bit" variant: is the shift amount, in the range 0 to 63, defaulting to 0 and encoded in the "imm6" field.

<Xd>	Is the 64-bit name of the general-purpose destination register, encoded in the "Rd" field.

<Xn>	Is the 64-bit name of the first general-purpose source register, encoded in the "Rn" field.

<Xm>	Is the 64-bit name of the second general-purpose source register, encoded in the "Rm" field.

Alias Conditions

Alias	Is preferred when
CMP (shifted register)	Rd == '11111'
NEGS	Rn == '11111' && Rd != '11111'

Operation

let operand1 : bits(datasize) = X{}(n); let operand2 : bits(datasize) = NOT(ShiftReg{datasize}(m, shift_type, shift_amount)); var result : bits(datasize); var nzcv : bits(4); (result, nzcv) = AddWithCarry{datasize}(operand1, operand2, '1'); X{datasize}(d) = result; PSTATE.[N,Z,C,V] = nzcv;

Operational information

This instruction is a data-independent-time instruction as described in About PSTATE.DIT.

2026-03_rel 2026-03-26 20:48:11

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sf	1	1	0	1	0	1	1	shift		0	Rm					imm6						Rn					Rd
	op	S