qsub

Saturating Subtract (A32)

QSUB<c> <Rd>, <Rm>, <Rn>

Subtracts two values and saturates the result.

Pseudocode Operation

result ← Rn - Rm; if SignedOverflow(result) then Rd ← Saturate(result) else Rd ← result

Example

QSUB r0, r2, r1

Encoding

Binary Layout

cond

31:28

00010

27:23

01

22:21

0

20

Rn

19:16

Rd

15:12

0

11

0

10

0

9

0

8

0101

7:4

Rm

3:0

 

Format Data Proc

Opcode 0x01200050

Extension A32 (Sat)

Operands

• Rd
  Destination general-purpose register
• Rm
  Second source / offset general-purpose register
• Rn
  First source / base general-purpose register

Related

More in A32 (Sat)

Reference

View in Arm A64 ISA Reference ↗ Arm AArch32 ISA

Instruction Forms

Encoding	Instruction		ISA		Bit pattern
0x01200050	QSUB{<c>}{<q>} {<Rd>,} <Rm>, <Rn>		A32		cond | 00010 | 01 | 0 | Rn | Rd | 0 | 0 | 0 | 0 | 0101 | Rm
0xFA80F0A0	QSUB{<c>}{<q>} {<Rd>,} <Rm>, <Rn>		T32		111110101 | 000 | Rn | 1111 | Rd | 10 | 10 | Rm

Description

Saturating Subtract subtracts one register value from another register value, saturates the result to the 32-bit signed integer range -231 <= x <= 231 - 1, and writes the result to the destination register. If saturation occurs, it sets PSTATE.Q to 1.

Operation

if ConditionPassed() then
    EncodingSpecificOperations();
    boolean sat;
    (R[d], sat) = SignedSatQ(SInt(R[m]) - SInt(R[n]), 32);
    if sat then
        PSTATE.Q = '1';