envutil_dispatch.cc

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/*            Copyright 2024 by Kay F. Jahnke                           */
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// this file handles the dispatch to ISA-specific code. This only makes
// sense for code which benefits from SIMD, the remainder of the program,
// which deals with I/O and arguments, can be compiled with a single
// common-denominator ISA.

#include "envutil_dispatch.h"

#undef HWY_TARGET_INCLUDE
#define HWY_TARGET_INCLUDE "envutil_dispatch.cc" 

#include <hwy/foreach_target.h> 
#include <hwy/highway.h>

HWY_BEFORE_NAMESPACE() ;

namespace project
{
  namespace HWY_NAMESPACE
  {
    // there isn't any payload code in this file - the implementations
    // of the ISA-specific derived 'dispatch' classes is coded in
    // envutil_payload.cc. Since all we ever 'get to see' in the part
    // of the code which obtains and uses dispatching are pointers to
    // dispatch_base, we needn't declare the derived class 'dispatch'.

    // _get_dispatch is declared here, because we'll use HWY_EXPORT
    // and HWY_DYNAMIC_DISPATCH in this file

    const dispatch_base * const _get_dispatch() ;
  } ;
} ;

HWY_AFTER_NAMESPACE() ;

#if HWY_ONCE

namespace project
{
  // we're using highway's foreach_target mechanism. To get access to the
  // SIMD-ISA-specific variant of _get_dispatch (in project::HWY_NAMESPACE)
  // we use the HWY_EXPORT macro:

  HWY_EXPORT ( _get_dispatch ) ;

  // now we can code get_dispatch: it simply uses HWY_DYNAMIC_DISPATCH
  // to pick the SIMD-ISA-specific _get_dispatch variant, which in turn
  // yields the desired dispatch_base pointer.
  // The main program calls 'get_dispatch' and receives a dispatch_base
  // pointer, which can be used to route to ISA-specific code best suited
  // for the CPU running the code:
  // auto dp = get_dispatch() ;
  // dp->payload ( ... ) ;

  const dispatch_base * const get_dispatch()
  {
    return HWY_DYNAMIC_DISPATCH ( _get_dispatch ) () ;
  }

} ;

#endif