FMLSL, FMLSL2 (vector)

Floating-point fused multiply-subtract long from accumulator (vector)

This instruction negates the half-precision values in the vector of one SIMD&FP register, multiplies these with the corresponding half-precision values in another vector, 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.


Note

ID_AA64ISAR0_EL1.FHM indicates whether this instruction is supported.


It has encodings from 2 classes: FMLSL and FMLSL2

FMLSL
(FEAT_FHM)

313029282726252423222120191817161514131211109876543210
0Q001110101Rm111011RnRd
USszopcode

Encoding

FMLSL <Vd>.<Ta>, <Vn>.<Tb>, <Vm>.<Tb>

Decode for this encoding

if !IsFeatureImplemented(FEAT_FHM) then EndOfDecode(Decode_UNDEF); end; if sz == '1' then EndOfDecode(Decode_UNDEF); end; let d : integer{} = UInt(Rd); let n : integer{} = UInt(Rn); let m : integer{} = UInt(Rm); let esize : integer{} = 32; let datasize : integer{} = 64 << UInt(Q); let elements : integer = datasize DIV esize; let part : integer = 0;

FMLSL2
(FEAT_FHM)

313029282726252423222120191817161514131211109876543210
0Q101110101Rm110011RnRd
USszopcode

Encoding

FMLSL2 <Vd>.<Ta>, <Vn>.<Tb>, <Vm>.<Tb>

Decode for this encoding

if !IsFeatureImplemented(FEAT_FHM) then EndOfDecode(Decode_UNDEF); end; if sz == '1' then EndOfDecode(Decode_UNDEF); end; let d : integer{} = UInt(Rd); let n : integer{} = UInt(Rn); let m : integer{} = UInt(Rm); let esize : integer{} = 32; let datasize : integer{} = 64 << UInt(Q); let elements : integer = datasize DIV esize; let part : integer = 1;

Assembler Symbols

<Vd>

Is the name of the SIMD&FP destination register, encoded in the "Rd" field.

<Ta>

Is an arrangement specifier, encoded in Q:

Q <Ta>
0 2S
1 4S
<Vn>

Is the name of the first SIMD&FP source register, encoded in the "Rn" field.

<Tb>

Is an arrangement specifier, encoded in Q:

Q <Tb>
0 2H
1 4H
<Vm>

Is the name of the second SIMD&FP source register, encoded in the "Rm" field.

Operation

AArch64_CheckFPAdvSIMDEnabled(); let operand1 : bits(datasize DIV 2) = Vpart{}(n, part); let operand2 : bits(datasize DIV 2) = Vpart{}(m, part); let operand3 : bits(datasize) = V{}(d); var result : bits(datasize); var element1 : bits(esize DIV 2); var element2 : bits(esize DIV 2); for e = 0 to elements-1 do element1 = FPNeg{esize DIV 2}(operand1[e*:(esize DIV 2)], FPCR()); element2 = operand2[e*:(esize DIV 2)]; result[e*:esize] = FPMulAddH(operand3[e*:esize], element1, element2, FPCR()); end; V{datasize}(d) = result;


2026-03_rel 2026-03-26 20:48:11

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