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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.

313029282726252423222120191817161514131211109876543210
00000101size100000101PgZnRd
B
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

<R> Is a width specifier, encoded in size:
size <R>
01 W
x0 W
11 X
<d>

Is the number [0-30] of the destination general-purpose register or the name ZR (31), encoded in the "Rd" field.

<Pg>

Is the name of the governing scalable predicate register P0-P7, encoded in the "Pg" field.

<Zn>

Is the name of the source scalable vector register, encoded in the "Zn" field.

<T> Is the size specifier, encoded in size:
size <T>
00 B
01 H
10 S
11 D

Operation

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;