PEXT (predicate)

Predicate extract from predicate-as-counter

Converts the source predicate-as-counter into a four register wide predicate-as-mask, and copies the portion of the mask value selected by the portion index to the destination predicate register. A portion corresponds to a one predicate register fraction of the wider predicate-as-mask value.

Encoding: SVE2

Variants: FEAT_SME2 || FEAT_SVE2p1 (FEAT_SME2 || FEAT_SVE2p1)

31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
0	0	1	0	0	1	0	1			1	0	0	0	0	0	0	1	1	1	0	0						1
								size														imm2		PNn				Pd

PEXT <Pd>.<T>, <PNn>[<imm>]

Decoding algorithm

if !IsFeatureImplemented(FEAT_SME2) && !IsFeatureImplemented(FEAT_SVE2p1) then
    EndOfDecode(Decode_UNDEF);
constant integer esize = 8 << UInt(size);
constant integer n = UInt('1':PNn);
constant integer d = UInt(Pd);
constant integer part = UInt(imm2);

Operation

if IsFeatureImplemented(FEAT_SVE2p1) then CheckSVEEnabled(); else CheckStreamingSVEEnabled();
constant integer VL = CurrentVL;
constant integer PL = VL DIV 8;
constant integer elements = VL DIV esize;
constant bits(PL) pred = P[n, PL];
constant bits(PL*4) mask = CounterToPredicate(pred<15:0>, PL*4);
bits(PL) result;
constant integer psize = esize DIV 8;

for e = 0 to elements-1
    constant bit pbit = PredicateElement(mask, part * elements + e, esize);
    Elem[result, e, psize] = ZeroExtend(pbit, psize);

P[d, PL] = result;

Explanations

<Pd>: Is the name of the destination scalable predicate register, encoded in the "Pd" field.
<T>: <PNn>: Is the name of the first source scalable predicate register PN8-PN15, with predicate-as-counter encoding, encoded in the "PNn" field.
<imm>: Is the portion index, in the range 0 to 3, encoded in the "imm2" field.