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VFMS

Vector Fused Multiply Subtract negates the elements of one vector and multiplies them with the corresponding elements of another vector, adds the products to the corresponding elements of the destination vector, and places the results in the destination vector. The instruction does not round the result of the multiply before the addition.

Depending on settings in the CPACR, NSACR, HCPTR, and FPEXC registers, and the Security state and PE mode in which the instruction is executed, an attempt to execute the instruction might be UNDEFINED, or trapped to Hyp mode. For more information see Enabling Advanced SIMD and floating-point support.

It has encodings from the following instruction sets: A32 ( A1 and A2 ) and T32 ( T1 and T2 ) .

A1

Decode for all variants of this encoding

if Q == '1' && (Vd[0] == '1' || Vn[0] == '1' || Vm[0] == '1') then Undefined(); end; if sz == '1' && !IsFeatureImplemented(FEAT_FP16) then Undefined(); end; let advsimd : boolean = TRUE; let op1_neg : boolean = (op == '1'); let esize : integer{} = 32 >> UInt(sz); let elements : integer = 64 DIV esize; let d : integer = UInt(D::Vd); let n : integer = UInt(N::Vn); let m : integer = UInt(M::Vm); let regs : integer = if Q == '0' then 1 else 2;

A2

Decode for all variants of this encoding

if FPSCR().Len != '000' || FPSCR().Stride != '00' then Undefined(); end; if size == '00' || (size == '01' && !IsFeatureImplemented(FEAT_FP16)) then Undefined(); end; if size == '01' && cond != '1110' then UnpredictableProcedure(); end; let advsimd : boolean = FALSE; let op1_neg : boolean = (op == '1'); let esize : integer{} = 8 << UInt(size); let d : integer = if size == '11' then UInt(D::Vd) else UInt(Vd::D); let n : integer = if size == '11' then UInt(N::Vn) else UInt(Vn::N); let m : integer = if size == '11' then UInt(M::Vm) else UInt(Vm::M); let floating_point : boolean = ARBITRARY : boolean; let regs : integer = ARBITRARY : integer; let elements : integer = ARBITRARY : integer;

CONSTRAINED UNPREDICTABLE behavior

If size == '01' && cond != '1110', then one of the following behaviors must occur:

• The instruction is undefined.
• The instruction executes as if it passes the Condition code check.
• The instruction executes as NOP. This means it behaves as if it fails the Condition code check.

T1

Decode for all variants of this encoding

if Q == '1' && (Vd[0] == '1' || Vn[0] == '1' || Vm[0] == '1') then Undefined(); end; if sz == '1' && !IsFeatureImplemented(FEAT_FP16) then Undefined(); end; if sz == '1' && InITBlock() then UnpredictableProcedure(); end; let advsimd : boolean = TRUE; let op1_neg : boolean = (op == '1'); let esize : integer{} = 32 >> UInt(sz); let elements : integer = 64 DIV esize; let d : integer = UInt(D::Vd); let n : integer = UInt(N::Vn); let m : integer = UInt(M::Vm); let regs : integer = if Q == '0' then 1 else 2;

CONSTRAINED UNPREDICTABLE behavior

If sz == '1' && InITBlock(), then one of the following behaviors must occur:

• The instruction is undefined.
• The instruction executes as if it passes the Condition code check.
• The instruction executes as NOP. This means it behaves as if it fails the Condition code check.

T2

Decode for all variants of this encoding

if FPSCR().Len != '000' || FPSCR().Stride != '00' then Undefined(); end; if size == '00' || (size == '01' && !IsFeatureImplemented(FEAT_FP16)) then Undefined(); end; if size == '01' && InITBlock() then UnpredictableProcedure(); end; let advsimd : boolean = FALSE; let op1_neg : boolean = (op == '1'); let esize : integer{} = 8 << UInt(size); let d : integer = if size == '11' then UInt(D::Vd) else UInt(Vd::D); let n : integer = if size == '11' then UInt(N::Vn) else UInt(Vn::N); let m : integer = if size == '11' then UInt(M::Vm) else UInt(Vm::M); let floating_point : boolean = ARBITRARY : boolean; let regs : integer = ARBITRARY : integer; let elements : integer = ARBITRARY : integer;

CONSTRAINED UNPREDICTABLE behavior

If size == '01' && InITBlock(), then one of the following behaviors must occur:

• The instruction is undefined.
• The instruction executes as if it passes the Condition code check.
• The instruction executes as NOP. This means it behaves as if it fails the Condition code check.