LASTB (scalar)
Extract last element to general-purpose register
If there is an active element then extract the last active element from the final source vector register. If there are no active elements, extract the highest-numbered element. Then zero-extend and place the extracted element in the destination general-purpose register.
Green
True
0
0
0
0
0
1
0
1
1
0
0
0
0
1
1
0
1
LASTB <R><d>, <Pg>, <Zn>.<T>
if !IsFeatureImplemented(FEAT_SVE) && !IsFeatureImplemented(FEAT_SME) then UNDEFINED;
constant integer esize = 8 << UInt(size);
constant integer rsize = if esize < 64 then 32 else 64;
constant integer g = UInt(Pg);
constant integer n = UInt(Zn);
constant integer d = UInt(Rd);
constant boolean isBefore = TRUE;
<R>
Is a width specifier,
<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,
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(VL) operand = Z[n, VL];
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], rsize);
X[d, rsize] = result;