subp

Subtract Pointers

SUBP <Xd>, <Xn|SP>, <Xm|SP>

Subtracts pointers ignoring Tags.

Pseudocode Operation

Xd ← (Xn | SP)[55:0] - (Xm | SP)[55:0]

Example

SUBP x0, x1, x2

Encoding

Binary Layout

1

31

0

30

0

29

11010110

28:21

Xm

20:16

000000

15:10

Xn

9:5

Xd

4:0

 

Format Data Processing

Opcode 0x9AC00000

Extension MTE (Memory Tagging)

Operands

• Xd
  Destination 64-bit integer register
• Xn
  Ptr 1
• Xm
  Ptr 2

Related

More in MTE (Memory Tagging)

Reference

View in Arm A64 ISA Reference ↗ Arm A64 ISA

Instruction Forms

Encoding	Instruction		ISA		Bit pattern
0x9AC00000	SUBP <Xd>, <Xn|SP>, <Xm|SP>		A64		1 | 0 | 0 | 11010110 | Xm | 000000 | Xn | Xd

Description

Subtract Pointer subtracts the 56-bit address held in the second source register from the 56-bit address held in the first source register, sign-extends the result to 64-bits, and writes the result to the destination register.

Operation

bits(64) operand1 = if n == 31 then SP[] else X[n, 64];
bits(64) operand2 = if m == 31 then SP[] else X[m, 64];
operand1 = SignExtend(operand1<55:0>, 64);
operand2 = SignExtend(operand2<55:0>, 64);

bits(64) result;

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

X[d, 64] = result;