LASTB (SIMD&FP scalar)

Extract last element to SIMD&FP scalar register

This instruction extracts the Last active element to a SIMD&FP scalar register. If there is an Active element, the Last active element from the final source vector register is extracted. If there are no Active elements, the highest-numbered element is extracted. Then the extracted element is placed in the destination SIMD&FP register.

SVE class

(FEAT_SVE || FEAT_SME)

31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
0	0	0	0	0	1	0	1	size		1	0	0	0	1	1	1	0	0	Pg			Zn					Vd
															B

Encoding

LASTB <V><d>, <Pg>, <Zn>.<T>

Decode

if !IsFeatureImplemented(FEAT_SVE) && !IsFeatureImplemented(FEAT_SME) then EndOfDecode(Decode_UNDEF); constant integer esize = 8 << UInt(size); constant integer g = UInt(Pg); constant integer n = UInt(Zn); constant integer d = UInt(Vd); constant boolean isBefore = TRUE;

Assembler Symbols

<V>

Is a width specifier, encoded in size:

size	<V>
00	B
01	H
10	S
11	D

<d>	Is the number [0-31] of the destination SIMD&FP register, encoded in the "Vd" 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(); 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]; 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; V[d, esize] = Elem[operand, last, esize];