ASR (immediate, predicated)

Arithmetic shift right by immediate (predicated)

Shift right by immediate, preserving the sign bit, each active element of the source vector, and destructively place the results in the corresponding elements of the source vector. The immediate shift amount is an unsigned value in the range 1 to number of bits per element. Inactive elements in the destination vector register remain unmodified.

Encoding: SVE

Variants: FEAT_SVE || FEAT_SME (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	0			0	0	0	0	0	0	1	0	0
								tszh				opc		L	U				Pg			tszl		imm3			Zdn

ASR <Zdn>.<T>, <Pg>/M, <Zdn>.<T>, #<const>

Decoding algorithm

if !IsFeatureImplemented(FEAT_SVE) && !IsFeatureImplemented(FEAT_SME) then
    EndOfDecode(Decode_UNDEF);
constant bits(4) tsize = tszh:tszl;
if tsize == '0000' then EndOfDecode(Decode_UNDEF);
constant integer esize = 8 << HighestSetBit(tsize);
constant integer g = UInt(Pg);
constant integer dn = UInt(Zdn);
constant integer shift = (2 * esize) - UInt(tsize:imm3);

Operation

CheckSVEEnabled();
constant integer VL = CurrentVL;
constant integer elements = VL DIV esize;
constant integer PL = VL DIV 8;
constant bits(VL) operand1 = Z[dn, VL];
constant bits(PL) mask = P[g, PL];
bits(VL) result;

for e = 0 to elements-1
    constant bits(esize) element1 = Elem[operand1, e, esize];
    if ActivePredicateElement(mask, e, esize) then
        Elem[result, e, esize] = ASR(element1, shift);
    else
        Elem[result, e, esize] = Elem[operand1, e, esize];

Z[dn, VL] = result;

Explanations

<Zdn>: Is the name of the source and destination scalable vector register, encoded in the "Zdn" field.
<T>: <Pg>: Is the name of the governing scalable predicate register P0-P7, encoded in the "Pg" field.
<const>: Is the immediate shift amount, in the range 1 to number of bits per element, encoded in "tszh:tszl:imm3".

Operational Notes

If PSTATE.DIT is 1:

• The execution time of this instruction is independent of:
  • The values of the data supplied in any of its operand registers when its governing predicate register contains the same value for each execution.
  • The values of the NZCV flags.
• The response of this instruction to asynchronous exceptions does not vary based on:
  • The values of the data supplied in any of its operand registers when its governing predicate register contains the same value for each execution.
  • The values of the NZCV flags.

This instruction might be immediately preceded in program order by a MOVPRFX instruction. The MOVPRFX must conform to all of the following requirements, otherwise the behavior of the MOVPRFX and this instruction is CONSTRAINED UNPREDICTABLE:

• The MOVPRFX can be predicated or unpredicated.
• A predicated MOVPRFX must use the same governing predicate register as this instruction.
• A predicated MOVPRFX must use the larger of the destination element size and first source element size in the preferred disassembly of this instruction.
• The MOVPRFX must specify the same destination register as this instruction.
• The destination register must not refer to architectural register state referenced by any other source operand register of this instruction.