Arm® A64 Instruction Set Architecture: Armv8, for Armv8-A architecture profile

PNEXT

Find next active predicate.

An instruction used to construct a loop which iterates over all active elements in a predicate. If all source predicate elements are false it sets the first active predicate element in the destination predicate to true. Otherwise it determines the next active predicate element following the last true source predicate element, and if one is found sets the corresponding destination predicate element to true. All other destination predicate elements are set to false. 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 << UInt(size);
integer g = UInt(Pg);
integer dn = UInt(Pdn);

Assembler Symbols

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

integer next = LastActiveElement(operand, esize) + 1;

while next < elements && (ElemP[mask, next, esize] == '0') do
    next = next + 1;

result = Zeros();
if next < elements then
    ElemP[result, next, esize] = '1';

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