src/google/protobuf/generated_message_tctable_decl.h

// Protocol Buffers - Google's data interchange format
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// This file contains declarations needed in generated headers for messages
// that use tail-call table parsing. Everything in this file is for internal
// use only.

#ifndef GOOGLE_PROTOBUF_GENERATED_MESSAGE_TCTABLE_DECL_H__
#define GOOGLE_PROTOBUF_GENERATED_MESSAGE_TCTABLE_DECL_H__

#include <cstdint>
#include <type_traits>

#include <google/protobuf/parse_context.h>
#include <google/protobuf/message_lite.h>

// Must come last:
#include <google/protobuf/port_def.inc>

namespace google {
namespace protobuf {
namespace internal {

// Additional information about this field:
struct TcFieldData {
  constexpr TcFieldData() : data(0) {}
  constexpr TcFieldData(uint16_t coded_tag, uint8_t hasbit_idx, uint16_t offset)
      : data(static_cast<uint64_t>(offset) << 48 |
             static_cast<uint64_t>(hasbit_idx) << 16 | coded_tag) {}

  template <typename TagType = uint16_t>
  TagType coded_tag() const {
    return static_cast<TagType>(data);
  }
  uint8_t hasbit_idx() const { return static_cast<uint8_t>(data >> 16); }
  uint16_t offset() const { return static_cast<uint16_t>(data >> 48); }

  uint64_t data;
};

struct TcParseTableBase;

// TailCallParseFunc is the function pointer type used in the tailcall table.
typedef const char* (*TailCallParseFunc)(PROTOBUF_TC_PARAM_DECL);

#if defined(_MSC_VER) && !defined(_WIN64)
#pragma warning(push)
// TcParseTableBase is intentionally overaligned on 32 bit targets.
#pragma warning(disable : 4324)
#endif

// Base class for message-level table with info for the tail-call parser.
struct alignas(uint64_t) TcParseTableBase {
  // Common attributes for message layout:
  uint16_t has_bits_offset;
  uint16_t extension_offset;
  uint32_t extension_range_low;
  uint32_t extension_range_high;
  uint8_t fast_idx_mask;
  uint8_t reserved;
  uint16_t num_fields;
  const MessageLite* default_instance;

  // Handler for fields which are not handled by table dispatch.
  TailCallParseFunc fallback;

  // Table entry for fast-path tailcall dispatch handling.
  struct FastFieldEntry {
    // Target function for dispatch:
    TailCallParseFunc target;
    // Field data used during parse:
    TcFieldData bits;
  };
  // There is always at least one table entry.
  const FastFieldEntry* fast_entry(size_t idx) const {
    return reinterpret_cast<const FastFieldEntry*>(this + 1) + idx;
  }
};

#if defined(_MSC_VER) && !defined(_WIN64)
#pragma warning(pop)
#endif

static_assert(sizeof(TcParseTableBase::FastFieldEntry) <= 16,
              "Field entry is too big.");

template <size_t kFastTableSizeLog2>
struct TcParseTable {
  TcParseTableBase header;

  // Entries for each field.
  //
  // Fields are indexed by the lowest bits of their field number. The field
  // number is masked to fit inside the table. Note that the parsing logic
  // generally calls `TailCallParseTableBase::table()` instead of accessing
  // this field directly.
  TcParseTableBase::FastFieldEntry entries[(1 << kFastTableSizeLog2)];
};

static_assert(std::is_standard_layout<TcParseTable<1>>::value,
              "TcParseTable must be standard layout.");

static_assert(offsetof(TcParseTable<1>, entries) == sizeof(TcParseTableBase),
              "Table entries must be laid out after TcParseTableBase.");

}  // namespace internal
}  // namespace protobuf
}  // namespace google

#include <google/protobuf/port_undef.inc>

#endif  // GOOGLE_PROTOBUF_GENERATED_MESSAGE_TCTABLE_DECL_H__