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VSTR

Store SIMD&FP register stores a single register from the Advanced SIMD and floating-point register file to memory, using an address from a general-purpose register, with an optional offset.

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 T32 ( T1 ) .

A1

313029282726252423222120191817161514131211109876543210
!= 11111101UD00RnVd10sizeimm8
cond

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

VSTR{<c>}{<q>}.16 <Sd>, [<Rn>{, #{+/-}<imm>}]

Single-precision scalar (size == 10)

VSTR{<c>}{<q>}{.32} <Sd>, [<Rn>{, #{+/-}<imm>}]

Double-precision scalar (size == 11)

VSTR{<c>}{<q>}{.64} <Dd>, [<Rn>{, #{+/-}<imm>}]

if size == '00' || (size == '01' && !HaveFP16Ext()) then UNDEFINED;
if size == '01' && cond != '1110' then UNPREDICTABLE;
esize = 8 << UInt(size);  add = (U == '1');
imm32 = if esize == 16 then ZeroExtend(imm8:'0', 32) else ZeroExtend(imm8:'00', 32);
case size of
    when '01' d = UInt(Vd:D);
    when '10' d = UInt(Vd:D);
    when '11' d = UInt(D:Vd);
n = UInt(Rn);
if n == 15 && CurrentInstrSet() != InstrSet_A32 then UNPREDICTABLE;

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
11101101UD00RnVd10sizeimm8

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

VSTR{<c>}{<q>}.16 <Sd>, [<Rn>{, #{+/-}<imm>}]

Single-precision scalar (size == 10)

VSTR{<c>}{<q>}{.32} <Sd>, [<Rn>{, #{+/-}<imm>}]

Double-precision scalar (size == 11)

VSTR{<c>}{<q>}{.64} <Dd>, [<Rn>{, #{+/-}<imm>}]

if size == '00' || (size == '01' && !HaveFP16Ext()) then UNDEFINED;
if size == '01' && InITBlock()  then UNPREDICTABLE;
esize = 8 << UInt(size);  add = (U == '1');
imm32 = if esize == 16 then ZeroExtend(imm8:'0', 32) else ZeroExtend(imm8:'00', 32);
case size of
    when '01' d = UInt(Vd:D);
    when '10' d = UInt(Vd:D);
    when '11' d = UInt(D:Vd);
n = UInt(Rn);
if n == 15 && CurrentInstrSet() != InstrSet_A32 then UNPREDICTABLE;

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.

For more information about the constrained unpredictable behavior of this instruction, see Architectural Constraints on UNPREDICTABLE behaviors.

Assembler Symbols

<c>

See Standard assembler syntax fields.

<q>

See Standard assembler syntax fields.

.64

Is an optional data size specifier for 64-bit memory accesses that can be used in the assembler source code, but is otherwise ignored.

<Dd>

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

.32

Is an optional data size specifier for 32-bit memory accesses that can be used in the assembler source code, but is otherwise ignored.

<Sd>

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

<Rn>

Is the general-purpose base register, encoded in the "Rn" field. The PC can be used, but this is deprecated.

+/- Specifies the offset is added to or subtracted from the base register, defaulting to + if omitted and encoded in U:
U +/-
0 -
1 +
<imm>

For the single-precision scalar or double-precision scalar variants: is the optional unsigned immediate byte offset, a multiple of 4, in the range 0 to 1020, defaulting to 0, and encoded in the "imm8" field as <imm>/4.

For the half-precision scalar variant: is the optional unsigned immediate byte offset, a multiple of 2, in the range 0 to 510, defaulting to 0, and encoded in the "imm8" field as <imm>/2.

Operation

if ConditionPassed() then
    EncodingSpecificOperations();  CheckVFPEnabled(TRUE);
    address = if add then (R[n] + imm32) else (R[n] - imm32);
    case esize of
        when 16
            MemA[address,2] = S[d]<15:0>;
        when 32
            MemA[address,4] = S[d];
        when 64
            // Store as two word-aligned words in the correct order for current endianness.
            MemA[address,4]   = if BigEndian() then D[d]<63:32> else D[d]<31:0>;
            MemA[address+4,4] = if BigEndian() then D[d]<31:0>  else D[d]<63:32>;
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