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SQDMLALT (indexed)

Signed saturating doubling multiply-add long to accumulator (top, indexed).

Multiply then double the odd-numbered signed elements within each 128-bit segment of the first source vector and the specified signed element in the corresponding second source vector segment. 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.

The elements within the second source vector are specified using an immediate index which selects the same element position within each 128-bit vector segment. The index range is from 0 to one less than the number of elements per 128-bit segment, encoded in 2 or 3 bits depending on the size of the element.

It has encodings from 2 classes: 32-bit and 64-bit

32-bit

313029282726252423222120191817161514131211109876543210
01000100101i3hZm0010i3l1ZnZda

32-bit

SQDMLALT <Zda>.S, <Zn>.H, <Zm>.H[<imm>]

if !HaveSVE2() then UNDEFINED;
integer esize = 16;
integer index = UInt(i3h:i3l);
integer n = UInt(Zn);
integer m = UInt(Zm);
integer da = UInt(Zda);
integer sel = 1;

64-bit

313029282726252423222120191817161514131211109876543210
01000100111i2hZm0010i2l1ZnZda

64-bit

SQDMLALT <Zda>.D, <Zn>.S, <Zm>.S[<imm>]

if !HaveSVE2() then UNDEFINED;
integer esize = 32;
integer index = UInt(i2h:i2l);
integer n = UInt(Zn);
integer m = UInt(Zm);
integer da = UInt(Zda);
integer sel = 1;

Assembler Symbols

<Zda>

Is the name of the third source and destination scalable vector register, encoded in the "Zda" field.

<Zn>

Is the name of the first source scalable vector register, encoded in the "Zn" field.

<Zm>

For the 32-bit variant: is the name of the second source scalable vector register Z0-Z7, encoded in the "Zm" field.

For the 64-bit variant: is the name of the second source scalable vector register Z0-Z15, encoded in the "Zm" field.

<imm>

For the 32-bit variant: is the element index, in the range 0 to 7, encoded in the "i3h:i3l" fields.

For the 64-bit variant: is the element index, in the range 0 to 3, encoded in the "i2h:i2l" fields.

Operation

CheckSVEEnabled();
integer elements = VL DIV (2 * esize);
integer eltspersegment = 128 DIV (2 * esize);
bits(VL) operand1 = Z[n];
bits(VL) operand2 = Z[m];
bits(VL) result = Z[da];

for e = 0 to elements-1
    integer s = e - e MOD eltspersegment;
    integer element1 = SInt(Elem[operand1, 2 * e + sel,   esize]);
    integer element2 = SInt(Elem[operand2, 2 * s + index, esize]);
    integer element3 = SInt(Elem[result, e, 2*esize]);
    integer product = SInt(SignedSat(2 * element1 * element2, 2*esize));
    integer res = element3 + product;
    Elem[result, e, 2*esize] = SignedSat(res, 2*esize);

Z[da] = result;

Operational information

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 that conforms to all of the following requirements, otherwise the behavior of either or both instructions is unpredictable:

  • The MOVPRFX instruction 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.
The MOVPRFX instructions that can be used with this instruction are as follows:
  • An unpredicated MOVPRFX instruction.
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