Arm® A64 Instruction Set Architecture: Future Architecture Technologies in the A architecture profile

PFIRST

Set the first active predicate element to true.

Sets the first active element in the destination predicate to true, otherwise elements from the source predicate are passed through unchanged. Sets the First (N), None (Z), !Last (C) condition flags based on the predicate result, and the V flag to zero.

if !HaveSVE() then UNDEFINED;
integer esize = 8;
integer g = UInt(Pg);
integer dn = UInt(Pdn);

Assembler Symbols

CheckSVEEnabled();
integer elements = VL DIV esize;
bits(PL) mask = P[g];
bits(PL) result = P[dn];
integer first = -1;

for e = 0 to elements-1
    if ElemP[mask, e, esize] == '1' && first == -1 then
        first = e;

if first >= 0 then
    ElemP[result, first, esize] = '1';

PSTATE.<N,Z,C,V> = PredTest(mask, result, esize);
P[dn] = result;