fabs

Floating-Point Absolute Value (Half-Precision)

FABS <Vd>.8H, <Vn>.8H

Absolute value of half-precision vector.

Pseudocode Operation

for i = 0 to 7
  Vd[i*16 +: 16] ← Vn[i*16 +: 16] AND 0x7FFF

Example

FABS v0.4s.8H, v1.4s.8H

Encoding

Binary Layout
0
31
Q
30
0
29
01110
28:24
1
23
111100
22:17
01111
16:12
10
11:10
Rn
9:5
Rd
4:0
 
Format NEON FP16
Opcode 0x0EF8F800
Extension FEAT_FP16 (NEON)

Operands

  • Vd
    Destination SIMD/FP vector register
  • Vn
    First source SIMD/FP vector register

Related

Other forms of fabs

  • fabs SVE Floating-Point Absolute Value
  • fabs Floating-Point Absolute Value (Scalar)
  • fabs Vector Floating-Point Absolute Value

More in FEAT_FP16 (NEON)

Reference

View in Arm A64 ISA Reference ↗ Arm A64 ISA

Instruction Forms

Encoding Instruction ISA Bit pattern
0x0EF8F800 FABS <Vd>.<T>, <Vn>.<T> A64 0 | Q | 0 | 01110 | 1 | 111100 | 01111 | 10 | Rn | Rd
0x0EA0F800 FABS <Vd>.<T>, <Vn>.<T> A64 0 | Q | 0 | 011101 | sz | 10000 | 01111 | 10 | Rn | Rd
0x1EE0C000 FABS <Hd>, <Hn> A64 0 | 0 | 0 | 11110 | 11 | 10000 | 01 | 10000 | Rn | Rd
0x1E20C000 FABS <Sd>, <Sn> A64 0 | 0 | 0 | 11110 | 00 | 10000 | 01 | 10000 | Rn | Rd
0x1E60C000 FABS <Dd>, <Dn> A64 0 | 0 | 0 | 11110 | 01 | 10000 | 01 | 10000 | Rn | Rd
0x041CA000 FABS <Zd>.<T>, <Pg>/M, <Zn>.<T> A64 00000100 | size | 011 | 10 | 0 | 101 | Pg | Zn | Zd

Description

Floating-point Absolute value (vector). This instruction calculates the absolute value of each vector element in the source SIMD&FP register, writes the result to a vector, and writes the vector to the destination SIMD&FP register. 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.

Operation

CheckFPAdvSIMDEnabled64();
bits(datasize) operand = V[n, datasize];
bits(datasize) result;
bits(esize) element;

for e = 0 to elements-1
    element = Elem[operand, e, esize];
    if neg then
        element = FPNeg(element, FPCR);
    else
        element = FPAbs(element, FPCR);
    Elem[result, e, esize] = element;

V[d, datasize] = result;