/*

* (C) 2023 Jack Lloyd

*

* Botan is released under the Simplified BSD License (see license.txt)

*/

#include <botan/internal/prefetch.h>

#include <botan/internal/bit_ops.h>

#include <new>

namespace Botan {

uint64_t prefetch_array_raw(size_t bytes, const void* arrayv) noexcept {

   // Android NDK is garbage and defines the feature macro, but not the variable

#if defined(__cpp_lib_hardware_interference_size) && !defined(BOTAN_TARGET_OS_IS_ANDROID)

   const size_t cache_line_size = std::hardware_destructive_interference_size;

#else

   // We arbitrarily use a 64 byte cache line, which is by far the most

   // common size.

   //

   // Runtime detection adds too much overhead to this function.

   const size_t cache_line_size = 64;

#endif

   const uint8_t* array = static_cast<const uint8_t*>(arrayv);

   volatile uint64_t combiner = 1;

   for(size_t idx = 0; idx < bytes; idx += cache_line_size) {

#if BOTAN_COMPILER_HAS_BUILTIN(__builtin_prefetch)

      // we have no way of knowing if the compiler will emit anything here

      __builtin_prefetch(&array[idx]);

#endif

      combiner = combiner | array[idx];

   }

   /*

   * The combiner variable is initialized with 1, and we accumulate using OR, so

   * now combiner must be a value other than zero. This being the case we will

   * always return zero here. Hopefully the compiler will not figure this out.

   */

   return ct_is_zero(combiner);

}

}  // namespace Botan