uqsub

Vector Unsigned Saturating Subtract

UQSUB <Vd>.<T>, <Vn>.<T>, <Vm>.<T>

Subtracts unsigned integers with saturation.

Pseudocode Operation

for i = 0 to elements_in_vector(Q, size) - 1 do
  if Vn[i] < Vm[i] then
    Vd[i] ← 0
  else
    Vd[i] ← Vn[i] - Vm[i]
  end if
end for

Example

UQSUB v0.4s.T, v1.4s.T, v2.4s.T

Encoding

Binary Layout

0

31

Q

30

1

29

01110

28:24

size

23:22

1

21

Rm

20:16

00101

15:11

1

10

Rn

9:5

Rd

4:0

 

Format SIMD Three Register

Opcode 0x2E202C00

Extension NEON (SIMD)

Operands

• Vd
  Destination SIMD/FP vector register
• Vn
  First source SIMD/FP vector register
• Vm
  Second source SIMD/FP vector register

Related

More in NEON (SIMD)

Reference

View in Arm A64 ISA Reference ↗ Arm A64 ISA

Instruction Forms

Encoding	Instruction		ISA		Bit pattern
0x7E202C00	UQSUB <V><d>, <V><n>, <V><m>		A64		01 | 1 | 11110 | size | 1 | Rm | 00101 | 1 | Rn | Rd
0x2E202C00	UQSUB <Vd>.<T>, <Vn>.<T>, <Vm>.<T>		A64		0 | Q | 1 | 01110 | size | 1 | Rm | 00101 | 1 | Rn | Rd
0x441B8000	UQSUB <Zdn>.<T>, <Pg>/M, <Zdn>.<T>, <Zm>.<T>		A64		01000100 | size | 011 | 0 | 1 | 1 | 100 | Pg | Zm | Zdn
0x2527C000	UQSUB <Zdn>.<T>, <Zdn>.<T>, #<imm>{, <shift>}		A64		00100101 | size | 100 | 11 | 1 | 11 | sh | imm8 | Zdn
0x04201C00	UQSUB <Zd>.<T>, <Zn>.<T>, <Zm>.<T>		A64		00000100 | size | 1 | Zm | 000 | 11 | 1 | Zn | Zd

Description

Unsigned saturating Subtract. This instruction subtracts the element values of the second source SIMD&FP register from the corresponding element values of the first source SIMD&FP register, places the results into a vector, and writes the vector to the destination SIMD&FP register. If overflow occurs with any of the results, those results are saturated. If saturation occurs, the cumulative saturation bit FPSR.QC is set. 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(datasize) operand1 = V[n, datasize];
bits(datasize) operand2 = V[m, datasize];
bits(datasize) result;
integer element1;
integer element2;
integer diff;
boolean sat;

for e = 0 to elements-1
    element1 = Int(Elem[operand1, e, esize], unsigned);
    element2 = Int(Elem[operand2, e, esize], unsigned);
    diff = element1 - element2;
    (Elem[result, e, esize], sat) = SatQ(diff, esize, unsigned);
    if sat then FPSR.QC = '1';

V[d, datasize] = result;