SUBS (shifted register) -- A64

Subtract (shifted register), setting flags, 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.

integer d = UInt(Rd); integer n = UInt(Rn); integer m = UInt(Rm); constant integer datasize = 32 << UInt(sf); if shift == '11' then UNDEFINED; if sf == '0' && imm6<5> == '1' then UNDEFINED; ShiftType shift_type = DecodeShift(shift); integer shift_amount = 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

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

Operational information

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.

Internal version only: aarchmrs v2023-12_rel, pseudocode v2023-12_rel, sve v2023-12_rel ; Build timestamp: 2023-12-15T16:46