cast.h

// Copyright 2025 The Pigweed Authors
//
// Licensed under the Apache License, Version 2.0 (the "License"); you may not
// use this file except in compliance with the License. You may obtain a copy of
// the License at
//
//     https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
// License for the specific language governing permissions and limitations under
// the License.
#pragma once
 
#include "pw_bytes/alignment.h"
#include "pw_span/internal/config.h"
#include "pw_span/span.h"
 
namespace pw {
namespace internal {
 
template <class ResultT, size_t kSourceExtentBytes>
using SpanFromBytes = span<ResultT,
                           (kSourceExtentBytes == dynamic_extent
                                ? dynamic_extent
                                : kSourceExtentBytes / sizeof(ResultT))>;
 
}  // namespace internal
 
 
template <class ResultT, size_t kSourceExtentBytes>
internal::SpanFromBytes<ResultT, kSourceExtentBytes> span_cast(
    span<std::byte, kSourceExtentBytes> bytes) {
  static_assert(sizeof(ResultT) == 1);
 
  ResultT* const ptr = reinterpret_cast<ResultT*>(bytes.data());
  const size_t count = bytes.size() / sizeof(ResultT);
 
  auto result =
      internal::SpanFromBytes<ResultT, kSourceExtentBytes>{ptr, count};
 
  _PW_SPAN_ASSERT(IsAlignedAs<ResultT>(result.data()));
  _PW_SPAN_ASSERT(result.size_bytes() == bytes.size_bytes());
 
  return result;
}
 
// TODO: https://pwbug.dev/396493663 - Doxygen thinks this is the same function
// as the non-const version above, and merges the docs together.
 
template <class ResultT, size_t kSourceExtentBytes>
internal::SpanFromBytes<const ResultT, kSourceExtentBytes> span_cast(
    span<const std::byte, kSourceExtentBytes> bytes) {
  static_assert(sizeof(ResultT) == 1);
 
  const ResultT* const ptr = reinterpret_cast<const ResultT*>(bytes.data());
  const size_t count = bytes.size() / sizeof(ResultT);
 
  auto result =
      internal::SpanFromBytes<const ResultT, kSourceExtentBytes>{ptr, count};
 
  _PW_SPAN_ASSERT(IsAlignedAs<const ResultT>(result.data()));
  _PW_SPAN_ASSERT(result.size_bytes() == bytes.size_bytes());
 
  return result;
}
 
 
}  // namespace pw