UABALB

Unsigned absolute difference and accumulate long (bottom)

Compute the absolute difference between even-numbered unsigned elements of the second source vector and corresponding elements of the first source vector, and destructively add to the overlapping double-width elements of the addend vector. This instruction is unpredicated.

Encoding: SVE2

Variants: FEAT_SVE2 || FEAT_SME (FEAT_SVE2 || 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	1	0	0	0	1	0	1			0						1	1	0	0	1	0
								size			Zm									U	T	Zn					Zda

UABALB <Zda>.<T>, <Zn>.<Tb>, <Zm>.<Tb>

Decoding algorithm

if !IsFeatureImplemented(FEAT_SVE2) && !IsFeatureImplemented(FEAT_SME) then
    EndOfDecode(Decode_UNDEF);
if size == '00' then EndOfDecode(Decode_UNDEF);
constant integer esize = 8 << UInt(size);
constant integer n = UInt(Zn);
constant integer m = UInt(Zm);
constant integer da = UInt(Zda);

Operation

CheckSVEEnabled();
constant integer VL = CurrentVL;
constant integer elements = VL DIV esize;
constant bits(VL) operand1 = Z[n, VL];
constant bits(VL) operand2 = Z[m, VL];
bits(VL) result = Z[da, VL];

for e = 0 to elements-1
    constant integer element1 = UInt(Elem[operand1, 2*e + 0, esize DIV 2]);
    constant integer element2 = UInt(Elem[operand2, 2*e + 0, esize DIV 2]);
    constant bits(esize) absdiff = Abs(element1 - element2);
    Elem[result, e, esize] = Elem[result, e, esize] + absdiff;

Z[da, VL] = result;

Explanations

<Zda>: Is the name of the third source and destination scalable vector register, encoded in the "Zda" field.
<T>: <Zn>: Is the name of the first source scalable vector register, encoded in the "Zn" field.
<Tb>: <Zm>: Is the name of the second source scalable vector register, encoded in the "Zm" field.

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 registers.
  • 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 registers.
  • 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 must be unpredicated.
• 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.