FABD

Floating-point absolute difference (vector)

This instruction subtracts the floating-point values in the elements of the second source SIMD&FP register, from the corresponding floating-point values in the elements of the first source SIMD&FP register, places the absolute value of each result in a vector, and writes the vector 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: Scalar half-precision

Variants: FEAT_AdvSIMD && FEAT_FP16 (FEAT_AdvSIMD && FEAT_FP16)

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	1	1	1	1	1	0	1	1	0						0	0	0	1	0	1
		U						a			Rm							opcode				Rn					Rd

FABD <Hd>, <Hn>, <Hm>

Decoding algorithm

if !IsFeatureImplemented(FEAT_AdvSIMD) || !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 = 16;
constant integer datasize = esize;
constant integer elements = 1;

Encoding: Scalar single-precision and double-precision

Variants: FEAT_AdvSIMD (ARMv8.0)

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	1	1	1	1	1	0	1		1						1	1	0	1	0	1
		U							sz		Rm					opcode						Rn					Rd

FABD <V><d>, <V><n>, <V><m>

Decoding algorithm

if !IsFeatureImplemented(FEAT_AdvSIMD) then EndOfDecode(Decode_UNDEF);
constant integer d = UInt(Rd);
constant integer n = UInt(Rn);
constant integer m = UInt(Rm);
constant integer esize = 32 << UInt(sz);
constant integer datasize = esize;
constant integer elements = 1;

Encoding: Vector half-precision

Variants: FEAT_AdvSIMD && FEAT_FP16 (FEAT_AdvSIMD && FEAT_FP16)

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	0	1	1	0						0	0	0	1	0	1
	Q	U						a			Rm							opcode				Rn					Rd

FABD <Vd>.<T>, <Vn>.<T>, <Vm>.<T>

Decoding algorithm

if !IsFeatureImplemented(FEAT_AdvSIMD) || !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 = 16;
constant integer datasize = 64 << UInt(Q);
constant integer elements = datasize DIV esize;

Encoding: Vector single-precision and double-precision

Variants: FEAT_AdvSIMD (ARMv8.0)

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	0	1		1						1	1	0	1	0	1
	Q	U							sz		Rm					opcode						Rn					Rd

FABD <Vd>.<T>, <Vn>.<T>, <Vm>.<T>

Decoding algorithm

if !IsFeatureImplemented(FEAT_AdvSIMD) then EndOfDecode(Decode_UNDEF);
if sz:Q == '10' then EndOfDecode(Decode_UNDEF);
constant integer d = UInt(Rd);
constant integer n = UInt(Rn);
constant integer m = UInt(Rm);
constant integer esize = 32 << UInt(sz);
constant integer datasize = 64 << UInt(Q);
constant integer elements = datasize DIV esize;

Operation

CheckFPAdvSIMDEnabled64();
constant bits(datasize) operand1 = V[n, datasize];
constant bits(datasize) operand2 = V[m, datasize];

bits(esize) element1;
bits(esize) element2;
constant boolean merge = elements == 1 && IsMerging(FPCR);
bits(128) result = if merge then V[n, 128] else Zeros(128);

for e = 0 to elements-1
    element1 = Elem[operand1, e, esize];
    element2 = Elem[operand2, e, esize];
    constant bits(esize) diff = FPSub(element1, element2, FPCR);
    Elem[result, e, esize] = FPAbs(diff, 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.
<V>: <d>: Is the number of the SIMD&FP destination register, encoded in the "Rd" field.
<n>: Is the number of the first SIMD&FP source register, encoded in the "Rn" field.
<m>: Is the number of the second SIMD&FP source register, encoded in the "Rm" field.
<Vd>: Is the name of the SIMD&FP destination register, encoded in the "Rd" field.
<T>: <T>: <Vn>: Is the name of the first SIMD&FP source register, encoded in the "Rn" field.
<Vm>: Is the name of the second SIMD&FP source register, encoded in the "Rm" field.