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.
Green
True
0
0
0
0
0
1
0
1
1
1
0
0
0
1
1
0
1
CLASTB <R><dn>, <Pg>, <R><dn>, <Zm>.<T>
if !IsFeatureImplemented(FEAT_SVE) && !IsFeatureImplemented(FEAT_SME) then UNDEFINED;
constant integer esize = 8 << UInt(size);
constant integer g = UInt(Pg);
constant integer dn = UInt(Rdn);
constant integer m = UInt(Zm);
constant integer csize = if esize < 64 then 32 else 64;
constant boolean isBefore = TRUE;
<R>
Is a width specifier,
<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,
size
<T>
00
B
01
H
10
S
11
D
CheckSVEEnabled();
constant integer VL = CurrentVL;
constant integer PL = VL DIV 8;
constant integer elements = VL DIV esize;
constant bits(PL) mask = P[g, PL];
constant bits(esize) operand1 = X[dn, esize];
constant bits(VL) operand2 = Z[m, VL];
bits(csize) result;
integer last = LastActiveElement(mask, esize);
if last < 0 then
result = ZeroExtend(operand1, csize);
else
if !isBefore then
last = last + 1;
if last >= elements then last = 0;
result = ZeroExtend(Elem[operand2, last, esize], csize);
X[dn, csize] = result;