You copied the Doc URL to your clipboard.

CLASTB (scalar)

Conditionally extract last element to general-purpose register.

From the source vector register extract the last active element, and then zero-extend that element to destructively place in the destination and first source general-purpose register. If there are no active elements then destructively zero-extend the least significant element-size bits of the destination and first source general-purpose register.

313029282726252423222120191817161514131211109876543210
00000101size110001101PgZmRdn
B
if !HaveSVE() then UNDEFINED;
integer esize = 8 << UInt(size);
integer g = UInt(Pg);
integer dn = UInt(Rdn);
integer m = UInt(Zm);
integer csize = if esize < 64 then 32 else 64;
boolean isBefore = TRUE;

Assembler Symbols

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

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

<Pg>

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

<Zm>

Is the name of the source scalable vector register, encoded in the "Zm" 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(esize) operand1 = X[dn];
bits(VL) operand2 = Z[m];
bits(csize) result;
integer last = LastActiveElement(mask, esize);

if last < 0 then
    result = ZeroExtend(operand1);
else
    if !isBefore then
        last = last + 1;
        if last >= elements then last = 0;
    result = ZeroExtend(Elem[operand2, last, esize]);

X[dn] = result;