CLASTB (SIMD&FP scalar)

Conditionally extract last element to SIMD&FP scalar register

This instruction extracts, from the source vector register, the Last active element, and then zero-extends that element to destructively place in the destination and first source SIMD & floating-point scalar register. If there are no Active elements, the least significant element-size bits of the destination and first source SIMD & floating-point scalar register are destructively zero-extended.

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	1	0	1	1	1	0	0	Pg			Zm					Vdn
															B

Encoding

CLASTB <V><dn>, <Pg>, <V><dn>, <Zm>.<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 dn = UInt(Vdn); constant integer m = UInt(Zm); constant boolean isBefore = TRUE;

Assembler Symbols

<V>

Is a width specifier, encoded in size:

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

<dn>	Is the number [0-31] of the source and destination SIMD&FP register, encoded in the "Vdn" 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(); 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 = V[dn, esize]; constant bits(VL) operand2 = Z[m, VL]; bits(esize) result; integer last = LastActiveElement(mask, esize); if last < 0 then result = ZeroExtend(operand1, esize); else if !isBefore then last = last + 1; if last >= elements then last = 0; result = Elem[operand2, last, esize]; V[dn, esize] = result;