FADD (scalar)

Floating-point add (scalar)

This instruction adds the floating-point values of the two source SIMD&FP registers, and writes the result to 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.

Encoding: Floating-point

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	0			1						0	0	1	0	1	0
M		S						ftype			Rm								op			Rn					Rd

Half-precision (ftype == 11)

FADD <Hd>, <Hn>, <Hm>

Single-precision (ftype == 00)

FADD <Sd>, <Sn>, <Sm>

Double-precision (ftype == 01)

FADD <Dd>, <Dn>, <Dm>

Decoding algorithm

if !IsFeatureImplemented(FEAT_FP) then EndOfDecode(Decode_UNDEF);
if ftype == '10' then EndOfDecode(Decode_UNDEF);
if ftype == '11' && !IsFeatureImplemented(FEAT_FP16) then EndOfDecode(Decode_UNDEF);

constant integer d = UInt(Rd);
constant integer n = UInt(Rn);
constant integer m = UInt(Rm);

constant integer esize = 8 << UInt(ftype EOR '10');

Operation

CheckFPEnabled64();
constant bits(esize) operand1 = V[n, esize];
constant bits(esize) operand2 = V[m, esize];

bits(128) result = if IsMerging(FPCR) then V[n, 128] else Zeros(128);

Elem[result, 0, esize] = FPAdd(operand1, operand2, FPCR);

V[d, 128] = result;

Explanations

<Hd>: Is the 16-bit name of the SIMD&FP destination register, encoded in the "Rd" field.
<Hn>: Is the 16-bit name of the first SIMD&FP source register, encoded in the "Rn" field.
<Hm>: Is the 16-bit name of the second SIMD&FP source register, encoded in the "Rm" field.
<Sd>: Is the 32-bit name of the SIMD&FP destination register, encoded in the "Rd" field.
<Sn>: Is the 32-bit name of the first SIMD&FP source register, encoded in the "Rn" field.
<Sm>: Is the 32-bit name of the second SIMD&FP source register, encoded in the "Rm" field.
<Dd>: Is the 64-bit name of the SIMD&FP destination register, encoded in the "Rd" field.
<Dn>: Is the 64-bit name of the first SIMD&FP source register, encoded in the "Rn" field.
<Dm>: Is the 64-bit name of the second SIMD&FP source register, encoded in the "Rm" field.