FMLAL, FMLAL2 (by element)

Floating-point fused multiply-add long to accumulator (by element)

This instruction multiplies the half-precision vector elements in the first source SIMD&FP register by the specified half-precision value in the second source SIMD&FP register, and accumulates the intermediate product without rounding to the corresponding single-precision vector element of the destination SIMD&FP register.

This instruction can generate a floating-point exception. Depending on the settings in FPCR, the exception results in either a flag being set in FPSR or a synchronous exception being generated. For more information, see Floating-point exceptions and exception traps.

Depending on the settings in the CPACR_EL1, CPTR_EL2, and CPTR_EL3 registers, and the current Security state and Exception level, an attempt to execute the instruction might be trapped.

In Armv8.2 and Armv8.3, this is an OPTIONAL instruction. From Armv8.4, it is mandatory for all implementations to support it.

ID_AA64ISAR0_EL1.FHM indicates whether this instruction is supported.

Encoding: FMLAL

Variants: FEAT_FHM (ARMv8.4)

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		0	0	1	1	1	1	1	0							0	0	0	0		0
	Q	U							sz	L	M	Rm					S			H		Rn					Rd

FMLAL <Vd>.<Ta>, <Vn>.<Tb>, <Vm>.H[<index>]

Decoding algorithm

if !IsFeatureImplemented(FEAT_FHM) then EndOfDecode(Decode_UNDEF);
if sz == '1' then EndOfDecode(Decode_UNDEF);
constant integer d = UInt(Rd);
constant integer n = UInt(Rn);
constant integer m = UInt('0':Rm);    // Vm can only be in bottom 16 registers.
constant integer index = UInt(H:L:M);

constant integer esize = 32;
constant integer datasize = 64 << UInt(Q);
constant integer elements = datasize DIV esize;

constant integer part = 0;

Encoding: FMLAL2

Variants: FEAT_FHM (ARMv8.4)

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	1	1	1	1	1	0							1	0	0	0		0
	Q	U							sz	L	M	Rm					S			H		Rn					Rd

FMLAL2 <Vd>.<Ta>, <Vn>.<Tb>, <Vm>.H[<index>]

Decoding algorithm

if !IsFeatureImplemented(FEAT_FHM) then EndOfDecode(Decode_UNDEF);
if sz == '1' then EndOfDecode(Decode_UNDEF);
constant integer d = UInt(Rd);
constant integer n = UInt(Rn);
constant integer m = UInt('0':Rm);    // Vm can only be in bottom 16 registers.
constant integer index = UInt(H:L:M);

constant integer esize = 32;
constant integer datasize = 64 << UInt(Q);
constant integer elements = datasize DIV esize;

constant integer part = 1;

Operation

CheckFPAdvSIMDEnabled64();
constant bits(datasize DIV 2) operand1 = Vpart[n, part, datasize DIV 2];
constant bits(128) operand2 = V[m, 128];
constant bits(datasize) operand3 = V[d, datasize];
bits(datasize) result;
bits(esize DIV 2) element1;
constant bits(esize DIV 2) element2 = Elem[operand2, index, esize DIV 2];

for e = 0 to elements-1
    element1 = Elem[operand1, e, esize DIV 2];
    Elem[result, e, esize] = FPMulAddH(Elem[operand3, e, esize], element1, element2, FPCR);
V[d, datasize] = result;

Explanations

<Vd>: Is the name of the SIMD&FP destination register, encoded in the "Rd" field.
<Ta>: <Vn>: Is the name of the first SIMD&FP source register, encoded in the "Rn" field.
<Tb>: <Vm>: Is the name of the second SIMD&FP source register, encoded in the "Rm" field.
<index>: Is the element index, encoded in the "H:L:M" fields.