fabs

Floating-Point Absolute Value (Scalar)

FABS <Hd|Sd|Dd>, <Hn|Sn|Dn>

Calculates the absolute value of a float.

Pseudocode Operation

Rd ← abs(Rn)
if (type == 00) then Rd is H-register (16-bit)
else if (type == 01) then Rd is S-register (32-bit)
else if (type == 10) then Rd is D-register (64-bit)

Example

FABS Dd, Dn

Encoding

Binary Layout
0
31
0
30
0
29
11110
28:24
00
23:22
10000
21:17
01
16:15
10000
14:10
Rn
9:5
Rd
4:0
 
Format FP Data Processing
Opcode 0x1E20C000
Extension Floating Point

Operands

  • Hd|Sd|Dd
    Destination SIMD&FP register (half, single or double-precision)
  • Hn|Sn|Dn
    First source SIMD&FP register (half, single or double-precision)

Related

Other forms of fabs

  • fabs SVE Floating-Point Absolute Value
  • fabs Vector Floating-Point Absolute Value
  • fabs Floating-Point Absolute Value (Half-Precision)

More in Floating Point

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 (scalar). This instruction calculates the absolute value in the SIMD&FP source register and writes the result to the SIMD&FP destination 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

CheckFPEnabled64();

boolean merge = IsMerging(FPCR);
bits(128) result = if merge then V[d, 128] else 0<127:0>;

bits(esize) operand = V[n, esize];

Elem[result, 0, esize] = FPAbs(operand, FPCR);
V[d, 128] = result;