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VRECPS

Vector Reciprocal Step multiplies the elements of one vector by the corresponding elements of another vector, subtracts each of the products from 2.0, and places the results into the elements of the destination vector.

The operand and result elements are floating-point numbers.

For details of the operation performed by this instruction see Floating-point reciprocal estimate and step.

Depending on settings in the CPACR, NSACR, and HCPTR 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 T32 ( T1 ) .

A1

313029282726252423222120191817161514131211109876543210
111100100D0szVnVd1111NQM1Vm

64-bit SIMD vector (Q == 0)

VRECPS{<c>}{<q>}.<dt> {<Dd>, }<Dn>, <Dm>

128-bit SIMD vector (Q == 1)

VRECPS{<c>}{<q>}.<dt> {<Qd>, }<Qn>, <Qm>

if Q == '1' && (Vd<0> == '1' || Vn<0> == '1' || Vm<0> == '1') then UNDEFINED;
if sz == '1' && !HaveFP16Ext() then UNDEFINED;
case sz of
    when '0' esize = 32; elements = 2;
    when '1' esize = 16; elements = 4;
d = UInt(D:Vd);  n = UInt(N:Vn);  m = UInt(M:Vm);  regs = if Q == '0' then 1 else 2;

T1

15141312111098765432101514131211109876543210
111011110D0szVnVd1111NQM1Vm

64-bit SIMD vector (Q == 0)

VRECPS{<c>}{<q>}.<dt> {<Dd>, }<Dn>, <Dm>

128-bit SIMD vector (Q == 1)

VRECPS{<c>}{<q>}.<dt> {<Qd>, }<Qn>, <Qm>

if Q == '1' && (Vd<0> == '1' || Vn<0> == '1' || Vm<0> == '1') then UNDEFINED;
if sz == '1' && !HaveFP16Ext() then UNDEFINED;
if sz == '1' && InITBlock() then UNPREDICTABLE;
case sz of
    when '0' esize = 32; elements = 2;
    when '1' esize = 16; elements = 4;
d = UInt(D:Vd);  n = UInt(N:Vn);  m = UInt(M:Vm);  regs = if Q == '0' then 1 else 2;

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 T1: see Standard assembler syntax fields.

<q>

See Standard assembler syntax fields.

<dt> Is the data type for the elements of the vectors, encoded in sz:
sz <dt>
0 F32
1 F16
<Qd>

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

<Qn>

Is the 128-bit name of the first SIMD&FP source register, encoded in the "N:Vn" field as <Qn>*2.

<Qm>

Is the 128-bit name of the second 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.

<Dn>

Is the 64-bit name of the first SIMD&FP source register, encoded in the "N:Vn" field.

<Dm>

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

Newton-Raphson iteration

For details of the operation performed and how it can be used in a Newton-Raphson iteration to calculate the reciprocal of a number, see Floating-point reciprocal estimate and step.

Operation

if ConditionPassed() then
    EncodingSpecificOperations();  CheckAdvSIMDEnabled();
    for r = 0 to regs-1
        for e = 0 to elements-1
            Elem[D[d+r],e,esize] = FPRecipStep(Elem[D[n+r],e,esize], Elem[D[m+r],e,esize]);