qdadd

Saturating Double and Add

QDADD<c> <Rd>, <Rm>, <Rn>

Doubles the second operand, adds to first, and saturates.

Pseudocode Operation

doubled ← SignedSat(Rm << 1, 32)
result ← SignedSat(Rn + doubled, 32)
Rd ← result
if (overflow during doubling or addition) then Q ← 1

Example

QDADD r0, r2, r1

Encoding

Binary Layout

cond

31:28

00010

27:23

10

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 0x01400050

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
0x01400050	QDADD{<c>}{<q>} {<Rd>,} <Rm>, <Rn>		A32		cond | 00010 | 10 | 0 | Rn | Rd | 0 | 0 | 0 | 0 | 0101 | Rm
0xFA80F090	QDADD{<c>}{<q>} {<Rd>,} <Rm>, <Rn>		T32		111110101 | 000 | Rn | 1111 | Rd | 10 | 01 | Rm

Description

Saturating Double and Add adds a doubled register value to another register value, and writes the result to the destination register. Both the doubling and the addition have their results saturated to the 32-bit signed integer range -231 <= x <= 231 - 1. If saturation occurs in either operation, it sets PSTATE.Q to 1.

Operation

if ConditionPassed() then
    EncodingSpecificOperations();
    (doubled, sat1) = SignedSatQ(2 * SInt(R[n]), 32);
    boolean sat2;
    (R[d], sat2)  = SignedSatQ(SInt(R[m]) + SInt(doubled), 32);
    if sat1 || sat2 then
        PSTATE.Q = '1';