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VFMAB, VFMAT (BFloat16, by scalar)

The BFloat16 floating-point widening multiply-add long instruction widens the even-numbered (bottom) or odd-numbered (top) 16-bit elements in the first source vector, and an indexed element in the second source vector from Bfloat16 to single-precision format. The instruction then multiplies and adds these values to the overlapping single-precision elements of the destination vector.

Unlike other BFloat16 multiplication instructions, this performs a fused multiply-add, without intermediate rounding that uses the Round to Nearest rounding mode and can generate a floating-point exception that causes cumulative exception bits in the FPSCR to be set.

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

A1
(Armv8.6)

313029282726252423222120191817161514131211109876543210
111111100D11VnVd1000NQM1Vm

A1

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

if !HaveAArch32BF16Ext() then UNDEFINED;
if Vd<0> == '1' || Vn<0> == '1' then UNDEFINED;
integer d = UInt(D:Vd);
integer n = UInt(N:Vn);
integer m = UInt(Vm<2:0>);
integer i = UInt(M:Vm<3>);
integer elements = 128 DIV 32;
integer sel = UInt(Q);

T1
(Armv8.6)

15141312111098765432101514131211109876543210
111111100D11VnVd1000NQM1Vm

T1

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

if InITBlock() then UNPREDICTABLE;
if !HaveAArch32BF16Ext() then UNDEFINED;
if Vd<0> == '1' || Vn<0> == '1' then UNDEFINED;
integer d = UInt(D:Vd);
integer n = UInt(N:Vn);
integer m = UInt(Vm<2:0>);
integer i = UInt(M:Vm<3>);
integer elements = 128 DIV 32;
integer sel = UInt(Q);

Assembler Symbols

<bt> Is the bottom or top element specifier, encoded in T:
T <bt>
0 B
1 T
<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.

<Dm>

Is the 64-bit name of the second SIMD&FP source register, encoded in the "Vm<2:0>" field.

<index>

Is the element index in the range 0 to 3, encoded in the "M:Vm<3>" field.

Operation

CheckAdvSIMDEnabled();
bits(128) operand1 = Q[n>>1];
bits(64) operand2 = D[m];
bits(128) operand3 = Q[d>>1];
bits(128) result;

bits(32) element2 = Elem[operand2, i, 16] : Zeros(16);

for e = 0 to elements-1
    bits(32) element1 = Elem[operand1, 2 * e + sel, 16] : Zeros(16);
    bits(32) addend = Elem[operand3, e, 32];
    Elem[result, e, 32] = FPMulAdd(addend, element1, element2,
                                   StandardFPSCRValue());

Q[d>>1] = result;
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