ADDHNB

Add narrow high part (bottom)

Add each vector element of the first source vector to the corresponding vector element of the second source vector, and place the most significant half of the result in the even-numbered half-width destination elements, while setting the odd-numbered elements to zero. This instruction is unpredicated.

Encoding: SVE2

Variants: FEAT_SVE2 || FEAT_SME (FEAT_SVE2 || FEAT_SME)

313029282726252423222120191817161514131211109876543210
010001011011000
sizeZmSRTZnZd

ADDHNB <Zd>.<T>, <Zn>.<Tb>, <Zm>.<Tb>

Decoding algorithm

if !IsFeatureImplemented(FEAT_SVE2) && !IsFeatureImplemented(FEAT_SME) then
    EndOfDecode(Decode_UNDEF);
if size == '00' then EndOfDecode(Decode_UNDEF);
constant integer esize = 8 << UInt(size);
constant integer n = UInt(Zn);
constant integer m = UInt(Zm);
constant integer d = UInt(Zd);

Operation

CheckSVEEnabled();
constant integer VL = CurrentVL;
constant integer elements = VL DIV esize;
constant bits(VL) operand1 = Z[n, VL];
constant bits(VL) operand2 = Z[m, VL];
bits(VL) result;
constant integer halfesize = esize DIV 2;

for e = 0 to elements-1
    constant integer element1 = UInt(Elem[operand1, e, esize]);
    constant integer element2 = UInt(Elem[operand2, e, esize]);
    constant integer res = (element1 + element2) >> halfesize;
    Elem[result, 2*e + 0, halfesize] = res;
    Elem[result, 2*e + 1, halfesize] = Zeros(halfesize);

Z[d, VL] = result;

Explanations

<Zd>: Is the name of the destination scalable vector register, encoded in the "Zd" field.
<T>: <Zn>: Is the name of the first source scalable vector register, encoded in the "Zn" field.
<Tb>: <Zm>: Is the name of the second source scalable vector register, encoded in the "Zm" field.

Operational Notes

If PSTATE.DIT is 1: