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

LASTA (scalar)

Extract element after last to general-purpose register.

If there is an active element then extract the element after the last active element modulo the number of elements from the final source vector register. If there are no active elements, extract element zero. Then zero-extend and place the extracted element in the destination general-purpose register.

if !HaveSVE() then UNDEFINED;
integer esize = 8 << UInt(size);
integer rsize = if esize < 64 then 32 else 64;
integer g = UInt(Pg);
integer n = UInt(Zn);
integer d = UInt(Rd);
boolean isBefore = FALSE;

Assembler Symbols

CheckSVEEnabled();
integer elements = VL DIV esize;
bits(PL) mask = P[g];
bits(VL) operand = Z[n];
bits(rsize) result;
integer last = LastActiveElement(mask, esize);

if isBefore then
    if last < 0 then last = elements - 1;
else
    last = last + 1;
    if last >= elements then last = 0;
result = ZeroExtend(Elem[operand, last, esize]);

X[d] = result;