uhsub

UHSUB <Zdn>.<T>, <Pg>/M, <Zdn>.<T>, <Zm>.<T>

Unsigned Halving Subtract.

Pseudocode Operation

No pseudocode available.

Encoding

Binary Layout
01000100
31:24
size
23:22
010
21:19
0
18
1
17
1
16
100
15:13
Pg
12:10
Zm
9:5
Zdn
4:0
 
Format SVE2
Opcode 0x44138000
Extension SVE2

Related

More in SVE2

Reference

View in Arm A64 ISA Reference ↗ Arm A64 ISA

Instruction Forms

Encoding Instruction ISA Bit pattern
0x2E202400 UHSUB <Vd>.<T>, <Vn>.<T>, <Vm>.<T> A64 0 | Q | 1 | 01110 | size | 1 | Rm | 00100 | 1 | Rn | Rd
0x44138000 UHSUB <Zdn>.<T>, <Pg>/M, <Zdn>.<T>, <Zm>.<T> A64 01000100 | size | 010 | 0 | 1 | 1 | 100 | Pg | Zm | Zdn

Description

Subtract active unsigned elements of the second source vector from corresponding unsigned elements of the first source vector, shift right one bit, and destructively place the results in the corresponding elements of the first source vector. Inactive elements in the destination vector register remain unmodified.

Operation

CheckSVEEnabled();
constant integer VL = CurrentVL;
constant integer PL = VL DIV 8;
constant integer elements = VL DIV esize;
bits(PL) mask = P[g, PL];
bits(VL) operand1 = Z[dn, VL];
bits(VL) operand2 = if AnyActiveElement(mask, esize) then Z[m, VL] else Zeros(VL);
bits(VL) result;

for e = 0 to elements-1
    integer element1 = UInt(Elem[operand1, e, esize]);
    integer element2 = UInt(Elem[operand2, e, esize]);
    if ActivePredicateElement(mask, e, esize) then
        integer res = (element1 - element2) >> 1;
        Elem[result, e, esize] = res<esize-1:0>;
    else
        Elem[result, e, esize] = Elem[operand1, e, esize];

Z[dn, VL] = result;