sbcs

Subtract with Carry and Set Flags

SBCS <Wd>, <Wn>, <Wm>

Subtracts with borrow and updates flags.

Pseudocode Operation

result ← Wn - Wm - (1 - C)
Wd ← result[31:0]
N ← result[31]
Z ← (result == 0)
C ← NOT(BorrowFrom(Wn - Wm - (1 - C)))
V ← OverflowFrom(Wn - Wm - (1 - C))

Example

SBCS w0, w1, w2

Encoding

Binary Layout

0

31

1

30

1

29

11010000

28:21

Rm

20:16

000000

15:10

Rn

9:5

Rd

4:0

 

Format Data Processing

Opcode 0x7A000000

Extension Base

Operands

• Wd
  Destination 32-bit integer register
• Wn
  First source / base 32-bit integer register
• Wm
  Second source / offset 32-bit integer register

Related

More in Base

Reference

View in Arm A64 ISA Reference ↗ Arm A64 ISA

Instruction Forms

Encoding	Instruction		ISA		Bit pattern
0x7A000000	SBCS <Wd>, <Wn>, <Wm>		A64		0 | 1 | 1 | 11010000 | Rm | 000000 | Rn | Rd
0xFA000000	SBCS <Xd>, <Xn>, <Xm>		A64		1 | 1 | 1 | 11010000 | Rm | 000000 | Rn | Rd

Description

Subtract with Carry, setting flags, subtracts a register value and the value of NOT (Carry flag) from a register value, and writes the result to the destination register. It updates the condition flags based on the result.

Operation

bits(datasize) result;
bits(datasize) operand1 = X[n, datasize];
bits(datasize) operand2 = X[m, datasize];
bits(4) nzcv;

operand2 = NOT(operand2);

(result, nzcv) = AddWithCarry(operand1, operand2, PSTATE.C);

PSTATE.<N,Z,C,V> = nzcv;

X[d, datasize] = result;