Index

SUB (immediate)

Subtract (immediate) subtracts an optionally-shifted immediate value from a register value, and writes the result to the destination register.

31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
sf 1 0 1 0 0 0 1 0 sh imm12 Rn Rd
op S

32-bit (sf == 0)

SUB <Wd|WSP>, <Wn|WSP>, #<imm>{, <shift>}

64-bit (sf == 1)

SUB <Xd|SP>, <Xn|SP>, #<imm>{, <shift>}

integer d = UInt(Rd);
integer n = UInt(Rn);
constant integer datasize = 32 << UInt(sf);
bits(datasize) imm;

case sh of
    when '0' imm = ZeroExtend(imm12, datasize);
    when '1' imm = ZeroExtend(imm12:Zeros(12), datasize);

Assembler Symbols

<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 source general-purpose register or stack pointer, encoded in the "Rn" field.
<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 source general-purpose register or stack pointer, encoded in the "Rn" field.
<imm>

Is an unsigned immediate, in the range 0 to 4095, encoded in the "imm12" field.
<shift>

Is the optional left shift to apply to the immediate, defaulting to LSL #0 and encoded in sh:

sh <shift>
0 LSL #0
1 LSL #12

Operation

bits(datasize) result;
bits(datasize) operand1 = if n == 31 then SP[]<datasize-1:0> else X[n, datasize];
bits(datasize) operand2;

operand2 = NOT(imm);
(result, -) = AddWithCarry(operand1, operand2, '1');

if d == 31 then
    SP[] = ZeroExtend(result, 64);
else
    X[d, datasize] = result;

Operational information

If PSTATE.DIT is 1: