CNTP (predicate)

Set scalar to count of true predicate elements

Counts the number of active and true elements in the source predicate and places the scalar result in the destination general-purpose register. Inactive predicate elements are not counted.

Encoding: SVE

Variants: FEAT_SVE || FEAT_SME (FEAT_SVE || FEAT_SME)

313029282726252423222120191817161514131211109876543210
00100101100000100
sizeopcPgPnRd

CNTP <Xd>, <Pg>, <Pn>.<T>

Decoding algorithm

if !IsFeatureImplemented(FEAT_SVE) && !IsFeatureImplemented(FEAT_SME) then
    EndOfDecode(Decode_UNDEF);
constant integer esize = 8 << UInt(size);
constant integer g = UInt(Pg);
constant integer n = UInt(Pn);
constant integer d = UInt(Rd);

Operation

CheckSVEEnabled();
constant integer VL = CurrentVL;
constant integer PL = VL DIV 8;
constant integer elements = VL DIV esize;
constant bits(PL) mask = P[g, PL];
constant bits(PL) operand = P[n, PL];
bits(64) sum = Zeros(64);

for e = 0 to elements-1
    if ActivePredicateElement(mask, e, esize) && ActivePredicateElement(operand, e, esize) then
        sum = sum + 1;
X[d, 64] = sum;

Explanations

<Xd>: Is the 64-bit name of the destination general-purpose register, encoded in the "Rd" field.
<Pg>: Is the name of the governing scalable predicate register, encoded in the "Pg" field.
<Pn>: Is the name of the source scalable predicate register, encoded in the "Pn" field.
<T>:

Operational Notes

If FEAT_SME is implemented and the PE is in Streaming SVE mode, then any subsequent instruction which is dependent on the general-purpose register written by this instruction might be significantly delayed.