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VDOT (by element)

BFloat16 floating-point indexed dot product (vector, by element). This instruction delimits the source vectors into pairs of 16-bit BF16 elements. Each pair of elements in the first source vector is multiplied by the indexed pair of elements in the second source vector. The resulting single-precision products are then summed and added destructively to the single-precision element in the destination vector which aligns with the pair of BFloat16 values in the first source vector. The instruction does not update the FPSCR exception status.

It has encodings from the following instruction sets: A32 ( A1 ) and T32 ( T1 ) .

A1
(Armv8.6)

313029282726252423222120191817161514131211109876543210
111111100D00VnVd1101NQM0Vm

64-bit SIMD vector (Q == 0)

VDOT{<q>}.BF16 <Dd>, <Dn>, <Dm>[<index>]

128-bit SIMD vector (Q == 1)

VDOT{<q>}.BF16 <Qd>, <Qn>, <Dm>[<index>]

if !HaveAArch32BF16Ext() then UNDEFINED;
if Q == '1' && (Vd<0> == '1' || Vn<0> == '1') then UNDEFINED;
integer d = UInt(D:Vd);
integer n = UInt(N:Vn);
integer m = UInt(Vm);
integer i = UInt(M);
integer regs = if Q == '1' then 2 else 1;

T1
(Armv8.6)

15141312111098765432101514131211109876543210
111111100D00VnVd1101NQM0Vm

64-bit SIMD vector (Q == 0)

VDOT{<q>}.BF16 <Dd>, <Dn>, <Dm>[<index>]

128-bit SIMD vector (Q == 1)

VDOT{<q>}.BF16 <Qd>, <Qn>, <Dm>[<index>]

if InITBlock() then UNPREDICTABLE;
if !HaveAArch32BF16Ext() then UNDEFINED;
if Q == '1' && (Vd<0> == '1' || Vn<0> == '1') then UNDEFINED;
integer d = UInt(D:Vd);
integer n = UInt(N:Vn);
integer m = UInt(Vm);
integer i = UInt(M);
integer regs = if Q == '1' then 2 else 1;

Assembler Symbols

<q>

See Standard assembler syntax fields.

<Qd>

Is the 128-bit name of the SIMD&FP destination register, encoded in the "D:Vd" field as <Qd>*2.

<Qn>

Is the 128-bit name of the first SIMD&FP source register, encoded in the "N:Vn" field as <Qn>*2.

<Dd>

Is the 64-bit name of the SIMD&FP destination register, encoded in the "D:Vd" field.

<Dn>

Is the 64-bit name of the first SIMD&FP source register, encoded in the "N:Vn" field.

<Dm>

Is the 64-bit name of the second SIMD&FP source register, encoded in the "Vm" field.

<index>

Is the element index in the range 0 to 1, encoded in the "M" field.

Operation

bits(64) operand1;
bits(64) operand2;
bits(64) result;

CheckAdvSIMDEnabled();

operand2 = Din[m];
for r = 0 to regs-1
    operand1 = Din[n+r];
    result = Din[d+r];
    for e = 0 to 1
        bits(16) elt1_a = Elem[operand1, 2 * e + 0, 16];
        bits(16) elt1_b = Elem[operand1, 2 * e + 1, 16];
        bits(16) elt2_a = Elem[operand2, 2 * i + 0, 16];
        bits(16) elt2_b = Elem[operand2, 2 * i + 1, 16];
        bits(32) sum = BFAdd(BFMul(elt1_a, elt2_a), BFMul(elt1_b, elt2_b));
        Elem[result, e, 32] = BFAdd(Elem[result, e, 32], sum);
    D[d+r] = result;
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