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VABS

Vector Absolute takes the absolute value of each element in a vector, and places the results in a second vector. The floating-point version only clears the sign bit.

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

313029282726252423222120191817161514131211109876543210
111100111D11size01Vd0F110QM0Vm

64-bit SIMD vector (Q == 0)

VABS{<c>}{<q>}.<dt> <Dd>, <Dm>

128-bit SIMD vector (Q == 1)

VABS{<c>}{<q>}.<dt> <Qd>, <Qm>

if size == '11' then UNDEFINED;
if F == '1' && ((size == '01' && !HaveFP16Ext()) || size == '00') then UNDEFINED;
if Q == '1' && (Vd<0> == '1' || Vm<0> == '1') then UNDEFINED;
advsimd = TRUE;  floating_point = (F == '1');
esize = 8 << UInt(size);  elements = 64 DIV esize;
d = UInt(D:Vd);  m = UInt(M:Vm);  regs = if Q == '0' then 1 else 2;

A2

313029282726252423222120191817161514131211109876543210
!= 111111101D110000Vd10size11M0Vm
cond

Half-precision scalar (size == 01)
(Armv8.2)

VABS{<c>}{<q>}.F16 <Sd>, <Sm>

Single-precision scalar (size == 10)

VABS{<c>}{<q>}.F32 <Sd>, <Sm>

Double-precision scalar (size == 11)

VABS{<c>}{<q>}.F64 <Dd>, <Dm>

if FPSCR.Len != '000' || FPSCR.Stride != '00' then UNDEFINED;
if size == '00' || (size == '01' && !HaveFP16Ext()) then UNDEFINED;
if size == '01' && cond != '1110' then UNPREDICTABLE;
advsimd = FALSE;
case size of
    when '01' esize = 16; d = UInt(Vd:D); m = UInt(Vm:M);
    when '10' esize = 32; d = UInt(Vd:D); m = UInt(Vm:M);
    when '11' esize = 64; d = UInt(D:Vd); m = UInt(M:Vm);

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

15141312111098765432101514131211109876543210
111111111D11size01Vd0F110QM0Vm

64-bit SIMD vector (Q == 0)

VABS{<c>}{<q>}.<dt> <Dd>, <Dm>

128-bit SIMD vector (Q == 1)

VABS{<c>}{<q>}.<dt> <Qd>, <Qm>

if size == '11' then UNDEFINED;
if F == '1' && ((size == '01' && !HaveFP16Ext()) || size == '00') then UNDEFINED;
if F == '1' && size == '01' && InITBlock() then UNPREDICTABLE;
if Q == '1' && (Vd<0> == '1' || Vm<0> == '1') then UNDEFINED;
advsimd = TRUE;  floating_point = (F == '1');
esize = 8 << UInt(size);  elements = 64 DIV esize;
d = UInt(D:Vd);  m = UInt(M:Vm);  regs = if Q == '0' then 1 else 2;

CONSTRAINED UNPREDICTABLE behavior

If F == '1' && 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.

T2

15141312111098765432101514131211109876543210
111011101D110000Vd10size11M0Vm

Half-precision scalar (size == 01)
(Armv8.2)

VABS{<c>}{<q>}.F16 <Sd>, <Sm>

Single-precision scalar (size == 10)

VABS{<c>}{<q>}.F32 <Sd>, <Sm>

Double-precision scalar (size == 11)

VABS{<c>}{<q>}.F64 <Dd>, <Dm>

if FPSCR.Len != '000' || FPSCR.Stride != '00' then UNDEFINED;
if size == '00' || (size == '01' && !HaveFP16Ext()) then UNDEFINED;
if size == '01' && InITBlock()  then UNPREDICTABLE;
advsimd = FALSE;
case size of
    when '01' esize = 16; d = UInt(Vd:D); m = UInt(Vm:M);
    when '10' esize = 32; d = UInt(Vd:D); m = UInt(Vm:M);
    when '11' esize = 64; d = UInt(D:Vd); m = UInt(M:Vm);

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.

Assembler Symbols

<c>

For encoding A1: see Standard assembler syntax fields. This encoding must be unconditional.

For encoding A2, T1 and T2: see Standard assembler syntax fields.

<q>

See Standard assembler syntax fields.

<dt> Is the data type for the elements of the vectors, encoded in F:size:
F size <dt>
0 00 S8
0 01 S16
0 10 S32
1 01 F16
1 10 F32
<Qd>

Is the 128-bit name of the SIMD&FP destination register, encoded in the "D:Vd" field as <Qd>*2.

<Qm>

Is the 128-bit name of the SIMD&FP source register, encoded in the "M:Vm" field as <Qm>*2.

<Dd>

Is the 64-bit name of the SIMD&FP destination register, encoded in the "D:Vd" field.

<Dm>

Is the 64-bit name of the SIMD&FP source register, encoded in the "M:Vm" field.

<Sd>

Is the 32-bit name of the SIMD&FP destination register, encoded in the "Vd:D" field.

<Sm>

Is the 32-bit name of the SIMD&FP source register, encoded in the "Vm:M" field.

Operation

if ConditionPassed() then
    EncodingSpecificOperations();  CheckAdvSIMDOrVFPEnabled(TRUE, advsimd);
    if advsimd then  // Advanced SIMD instruction
        for r = 0 to regs-1
            for e = 0 to elements-1
                if floating_point then
                    Elem[D[d+r],e,esize] = FPAbs(Elem[D[m+r],e,esize]);
                else
                    result = Abs(SInt(Elem[D[m+r],e,esize]));
                    Elem[D[d+r],e,esize] = result<esize-1:0>;
    else             // VFP instruction
        case esize of
            when 16 S[d] = Zeros(16) : FPAbs(S[m]<15:0>);
            when 32 S[d] = FPAbs(S[m]);
            when 64 D[d] = FPAbs(D[m]);

Operational information

If CPSR.DIT is 1 and this instruction passes its condition execution check:

  • The execution time of this instruction is independent of:
    • The values of the data supplied in any of its registers.
    • The values of the NZCV flags.
  • The response of this instruction to asynchronous exceptions does not vary based on:
    • The values of the data supplied in any of its registers.
    • The values of the NZCV flags.
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