SQDMLALB (vectors)

Signed saturating doubling multiply-add long to accumulator (bottom)

Multiply then double the corresponding even-numbered signed elements of the first and second source vectors. Each intermediate value is saturated to the double-width N-bit value's signed integer range -2(N-1) to (2(N-1))-1. Then destructively add to the overlapping double-width elements of the addend and destination vector. Each destination element is saturated to the double-width N-bit element's signed integer range -2(N-1) to (2(N-1))-1. 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	0			0						0	1	1	0	0	0
								size			Zm									S	T	Zn					Zda

SQDMLALB <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);
constant integer sel1 = 0;
constant integer sel2 = 0;

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 = SInt(Elem[operand1, 2 * e + sel1, esize DIV 2]);
    constant integer element2 = SInt(Elem[operand2, 2 * e + sel2, esize DIV 2]);
    constant integer element3 = SInt(Elem[result, e, esize]);
    constant integer product = SInt(SignedSat(2 * element1 * element2, esize));
    Elem[result, e, esize] = SignedSat(element3 + product, esize);

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

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.