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[ATfL] Add language/OpenMP support information to ATfL docs (#267)
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‎arm-software/linux/docs/GettingStarted.md‎

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`-mcpu=<target>` where `<target>` is the target processor that you will run
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the application on.
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### Standards support
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For information on C, C++, and Fortran language support in ATfL, see the [Standards Support page](StandardsSupport.md).
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For details on OpenMP support in ATfL, refer to the [OpenMP Support page](OpenMPSupport.md).
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### Fortran Recommendations
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#### Who should use Arm Toolchain For Linux

‎arm-software/linux/docs/OpenMPSupport.md‎

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# Clang OpenMP support
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Refer to the [status page](https://releases.llvm.org/20.1.0/tools/clang/docs/OpenMPSupport.html) for details on Clang OpenMP support.
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# Flang OpenMP Support
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This section outlines the OpenMP API features supported by Flang. It is intended as a general reference.
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For the most accurate information on unimplemented features, rely on the compiler’s TODO or “Not Yet Implemented”
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messages, which are considered authoritative. With the exception of a few corner cases, Flang
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offers full support for (OpenMP 2.5)[#openmp-25-openmp-11], and partial support for [OpenMP 3.1](#openmp-31-openmp-30)
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and [OpenMP 4.0](#openmp-40). The tables below outline the current status of OpenMP 4.0, 3.1, 3.0 feature support.
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Work is ongoing to add support for OpenMP 4.5 and newer versions; a support statement for these will be shared in the future.
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The feature support information is provided as a table with three columns that are self explanatory. The Status column uses
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the letters **P**, **Y**, **N** for the implementation status:
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- **P** : Partial. When the implementation is incomplete for a few cases
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- **Y** : Yes. When the implementation is complete
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- **N** : No. When the implementation is absent
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Note: No distinction is made between the support in Parser/Semantics, MLIR, Lowering or the OpenMPIRBuilder.
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## OpenMP 4.0
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| Feature | Status | Comments |
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|------------------------------------------------------------|--------|---------------------------------------------------------|
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| proc_bind clause | Y | |
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| simd construct | P | Some clauses are not supported |
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| declare simd construct | N | |
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| do simd construct | Y | |
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| target data construct | N | |
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| target construct | N | |
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| target update construct | N | |
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| declare target directive | N | |
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| teams construct | N | |
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| distribute construct | N | |
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| distribute simd construct | N | |
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| distribute parallel loop construct | N | |
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| distribute parallel loop simd construct | N | |
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| depend clause | P | Depend clause with array sections are not supported |
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| declare reduction construct | N | |
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| atomic construct extensions | Y | |
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| cancel construct | N | |
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| cancellation point construct | N | |
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| parallel do simd construct | Y | |
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| target teams construct | N | |
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| teams distribute construct | N | |
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| teams distribute simd construct | N | |
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| target teams distribute construct | N | |
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| teams distribute parallel loop construct | N | |
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| target teams distribute parallel loop construct | N | |
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| teams distribute parallel loop simd construct | N | |
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| target teams distribute parallel loop simd construct | N | |
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## OpenMP 3.1, OpenMP 3.0
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| Feature | Status | Comments |
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|------------------------------------------------------------|--------|---------------------------------------------------------|
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| intent(in) in firstprivate | Y | |
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| pointers in firstprivate and lastprivate | Y | |
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| final and mergeable clauses in task | Y | |
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| taskyield construct | Y | |
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| atomic construct extensions | Y | |
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| assumed-size arrays are shared | Y | |
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| allocatable arrays in private, firstprivate, lastprivate, reduction, copyin, copyprivate | Y | |
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| firstprivate in default | Y | |
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| collapse clause | Y | |
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| schedule kind auto | Y | |
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| task construct | P | delayed execution of tasks is not supported |
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| taskwait construct | Y | |
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## OpenMP 2.5, OpenMP 1.1
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All features except a few corner cases in atomic (complex type, different but compatible types in lhs and rhs), threadprivate (character type) constructs/clauses are supported.

‎arm-software/linux/docs/StandardsSupport.md‎

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# C Standard Support
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Refer to the [Clang C status page](https://clang.llvm.org/c_status.html) for details on C standard support.
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# C++ Standard Support
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Refer to the [Clang C++ status page](https://clang.llvm.org/cxx_status.html) for details on C++ standard support.
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# Fortran Standards Support
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This section summarizes Fortran standards support in Flang. The information is only provided as a guideline. The
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TODOs/Not Yet Implemented messages emitted by the compiler for unimplemented features should be treated as authoritative.
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The standards support information is provided as a table with three columns that are self explanatory. The Status column uses
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the letters **P**, **Y**, **N** for the implementation status:
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- **P** : When the implementation is incomplete for a few cases
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- **Y** : When the implementation is complete
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- **N** : When the implementation is absent
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Note: No distinction is made between the support in the Parser/Semantics and MLIR or Lowering support.
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## Fortran 2023
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See [this document](https://github.com/llvm/llvm-project/blob/main/flang/docs/F202X.md) for a brief discussion about the new features in Fortran 2023. The following table summarizes the
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status of all important Fortran 2023 features.
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| Feature | Status | Comments |
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|------------------------------------------------------------|--------|---------------------------------------------------------|
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| Allow longer statement lines and overall statement length | Y | |
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| Automatic allocation of lengths of character variables | N | |
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| The specifiers typeof and classof | N | |
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| Conditional expressions and arguments | N | |
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| More use of boz constants | P | All usages other than enum are supported |
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| Intrinsics for extracting tokens from a string | N | |
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| Intrinsics for Trig functions that work in degrees | N | |
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| Intrinsics for Trig functions that work in half revolutions| N | |
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| Changes to system_clock | N | |
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| Changes for conformance with the new IEEE standard | Y | |
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| Additional named constants to specify kinds | Y | |
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| Extensions for c_f_pointer intrinsic | N | |
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| Procedures for converting between fortran and c strings | N | |
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| The at edit descriptor | N | |
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| Control over leading zeros in output of real values | N | |
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| Extensions for Namelist | N | |
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| Allow an object of a type with a coarray ultimate component to be an array or allocatable | N | |
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| Put with Notify | N | |
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| Error conditions in collectives | N | |
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| Simple procedures | N | |
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| Using integer arrays to specify subscripts | N | |
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| Using integer arrays to specify rank and bound of an array | N | |
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| Using an integer constant to specify rank | N | |
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| Reduction specifier for do concurrent | P | Syntax is accepted |
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| Enumerations | N | |
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## Fortran 2018
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All features except those listed in the following table are supported. Almost all of the unsupported features are related to
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the multi-image execution.
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| Feature | Status | Comments |
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|------------------------------------------------------------|--------|---------------------------------------------------------|
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| Asynchronous communication | P | Syntax is accepted |
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| Teams | N | |
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| Image failure | P | stat_failed_image is added |
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| Form team statement | N | |
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| Change team construct | N | |
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| Coarrays allocated in teams | N | |
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| Critical construct | N | |
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| Lock and unlock statements | N | |
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| Events | N | |
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| Sync team construct | N | |
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| Image selectors | N | |
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| Intrinsic functions get_team and team_number | N | |
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| Intrinsic function image_index | N | |
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| Intrinsic function num_images | N | |
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| Intrinsic function this_image | N | |
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| Intrinsic move_alloc extensions | P | |
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| Detecting failed and stopped images | N | |
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| Collective subroutines | N | |
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| New and enhanced atomic subroutines | N | |
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| Failed images and stat= specifiers | N | |
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| Intrinsic function coshape | N | |
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## Fortran 2008
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All features except those listed in the following table are supported.
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| Feature | Status | Comments |
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|------------------------------------------------------------|--------|---------------------------------------------------------|
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| Coarrays | N | Lowering and runtime support is not implemented |
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| do concurrent | P | Sequential execution works. Parallel support in progress|
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| Internal procedure as an actual argument or pointer target | Y | Current implementation requires stack to be executable. See [Proposal](https://github.com/llvm/llvm-project/blob/main/flang/docs/InternalProcedureTrampolines.md) |
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## Fortran 2003
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All features except those listed in the following table are supported.
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| Feature | Status | Comments |
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|------------------------------------------------------------|--------|---------------------------------------------------------|
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| Parameterized Derived Types | P | PDT with length type parameters is not supported. See [Proposal](https://github.com/llvm/llvm-project/blob/main/flang/docs/ParameterizedDerivedTypes.md) |
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| Assignment to allocatable | P | Assignment to whole allocatable in FORALL is not implemented |
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| Pointer Assignment | P | Polymorphic assignment in FORALL is not implemented |
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| The VOLATILE attribute | P | VOLATILE in procedure interfaces is not implemented |
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| Asynchronous input/output | P | IO will happen synchronously |
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| MIN/MAX extensions for CHARACTER | P | Some variants are not supported |
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## Fortran 95
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All features are supported.
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## Fortran 90
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All features are supported.
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## FORTRAN 77
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All features are supported.

‎arm-software/linux/docs/index.md‎

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GettingStarted
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UsingArmPL
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PortingFromACfL
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StandardsSupport
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OpenMPSupport
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```

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