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## QSAX

Saturating Subtract and Add with Exchange exchanges the two halfwords of the second operand, performs one 16-bit integer subtraction and one 16-bit addition, saturates the results to the 16-bit signed integer range -215 <= x <= 215 - 1, and writes the results to the destination register.

It has encodings from the following instruction sets: A32 ( A1 ) and T32 ( T1 ) .

### A1

 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 != 1111 0 1 1 0 0 0 1 0 Rn Rd (1) (1) (1) (1) 0 1 0 1 Rm cond

#### A1

QSAX{<c>}{<q>} {<Rd>,} <Rn>, <Rm>

```d = UInt(Rd);  n = UInt(Rn);  m = UInt(Rm);
if d == 15 || n == 15 || m == 15 then UNPREDICTABLE;```

### T1

 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 1 1 1 1 1 0 1 0 1 1 1 0 Rn 1 1 1 1 Rd 0 0 0 1 Rm

#### T1

QSAX{<c>}{<q>} {<Rd>,} <Rn>, <Rm>

```d = UInt(Rd);  n = UInt(Rn);  m = UInt(Rm);
if d == 15 || n == 15 || m == 15 then UNPREDICTABLE; // Armv8-A removes UNPREDICTABLE for R13```

For more information about the constrained unpredictable behavior of this instruction, see Architectural Constraints on UNPREDICTABLE behaviors.

### Assembler Symbols



 Is the general-purpose destination register, encoded in the "Rd" field.
 Is the first general-purpose source register, encoded in the "Rn" field.
 Is the second general-purpose source register, encoded in the "Rm" field.

### Operation

```if ConditionPassed() then
EncodingSpecificOperations();
sum  = SInt(R[n]<15:0>) + SInt(R[m]<31:16>);
diff = SInt(R[n]<31:16>) - SInt(R[m]<15:0>);
R[d]<15:0>  = SignedSat(sum, 16);
R[d]<31:16> = SignedSat(diff, 16);```