saddw

Signed Add Wide

SADDW <Vd>.<Td>, <Vn>.<Td>, <Vm>.<Ts>

Adds a wide vector to the lower/upper half of a narrow vector.

Pseudocode Operation

if Q == 0 then
  half ← "lower"
else
  half ← "upper"
for i = 0 to (length(Vd) / element_width(Td)) - 1 do
  Vn_element ← Vn[i]
  Vm_element ← extract_half(Vm[i], half)
  Vd[i] ← signed_add(Vn_element, Vm_element)
N ← unaffected; Z ← unaffected; C ← unaffected; V ← unaffected

Example

SADDW v0.4s.Td, v1.4s.Td, v2.4s.Ts

Encoding

Binary Layout

01110

28:24

size

23:22

20:16

15:14

100

12:10

9:5

4:0

Format SIMD Three Register Diff

Opcode 0x0E201000

Extension NEON (SIMD)

Operands

Vd
Destination SIMD/FP vector register
Vn
Src Wide
Vm
Src Narrow

Reference

View in Arm A64 ISA Reference ↗ Arm A64 ISA

Instruction Forms

Encoding	Instruction		ISA		Bit pattern
0x0E201000	SADDW{2} <Vd>.<Ta>, <Vn>.<Ta>, <Vm>.<Tb>		A64		0 \| Q \| 0 \| 01110 \| size \| 1 \| Rm \| 00 \| 0 \| 100 \| Rn \| Rd

Description

Signed Add Wide. This instruction adds vector elements of the first source SIMD&FP register to the corresponding vector elements in the lower or upper half of the second source SIMD&FP register, places the results in a vector, and writes the vector to the SIMD&FP destination register. The SADDW instruction extracts the second source vector from the lower half of the second source register. The SADDW2 instruction extracts the second source vector from the upper half of the second source register. Depending on the settings in the CPACR_EL1, CPTR_EL2, and CPTR_EL3 registers, and the current Security state and Exception level, an attempt to execute the instruction might be trapped.

Operation

CheckFPAdvSIMDEnabled64();
bits(2*datasize) operand1 = V[n, 2*datasize];
bits(datasize) operand2 = Vpart[m, part, datasize];
bits(2*datasize) result;
integer element1;
integer element2;
integer sum;

for e = 0 to elements-1
    element1 = Int(Elem[operand1, e, 2*esize], unsigned);
    element2 = Int(Elem[operand2, e, esize], unsigned);
    if sub_op then
        sum = element1 - element2;
    else
        sum = element1 + element2;
    Elem[result, e, 2*esize] = sum<2*esize-1:0>;

V[d, 2*datasize] = result;