CLASTA (SIMD&FP scalar)

Conditionally extract element after last to SIMD&FP scalar register

This instruction extracts, from the source vector register, the element after the Last active element, or if the Last active element is the final element it extracts element zero, 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	0	1	0	0	Pg			Zm					Vdn
															B

Encoding

CLASTA <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 = FALSE;

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;