protobuf/upb/message/internal/array.h

// Protocol Buffers - Google's data interchange format
// Copyright 2023 Google LLC.  All rights reserved.
//
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file or at
// https://developers.google.com/open-source/licenses/bsd

#ifndef UPB_MESSAGE_INTERNAL_ARRAY_H_
#define UPB_MESSAGE_INTERNAL_ARRAY_H_

#include <string.h>

#include "upb/message/array.h"

// Must be last.
#include "upb/port/def.inc"

#define _UPB_ARRAY_MASK_IMM 0x4  // Frozen/immutable bit.
#define _UPB_ARRAY_MASK_LG2 0x3  // Encoded elem size.
#define _UPB_ARRAY_MASK_ALL (_UPB_ARRAY_MASK_IMM | _UPB_ARRAY_MASK_LG2)

#ifdef __cplusplus
extern "C" {
#endif

// LINT.IfChange(struct_definition)
// Our internal representation for repeated fields.
struct upb_Array {
  // This is a tagged pointer. Bits #0 and #1 encode the elem size as follows:
  //   0 maps to elem size 1
  //   1 maps to elem size 4
  //   2 maps to elem size 8
  //   3 maps to elem size 16
  //
  // Bit #2 contains the frozen/immutable flag (currently unimplemented).
  uintptr_t data;

  size_t size;      // The number of elements in the array.
  size_t capacity;  // Allocated storage. Measured in elements.
};
// LINT.ThenChange(GoogleInternalName1)

UPB_INLINE void _upb_Array_SetTaggedPtr(upb_Array* arr, void* data,
                                        size_t lg2) {
  UPB_ASSERT(lg2 != 1);
  UPB_ASSERT(lg2 <= 4);
  const size_t bits = lg2 - (lg2 != 0);
  arr->data = (uintptr_t)data | bits;
}

UPB_INLINE size_t _upb_Array_ElemSizeLg2(const upb_Array* arr) {
  const size_t bits = arr->data & _UPB_ARRAY_MASK_LG2;
  const size_t lg2 = bits + (bits != 0);
  return lg2;
}

UPB_INLINE const void* _upb_array_constptr(const upb_Array* arr) {
  _upb_Array_ElemSizeLg2(arr);  // Check assertions.
  return (void*)(arr->data & ~(uintptr_t)_UPB_ARRAY_MASK_ALL);
}

UPB_INLINE void* _upb_array_ptr(upb_Array* arr) {
  return (void*)_upb_array_constptr(arr);
}

UPB_INLINE upb_Array* _upb_Array_New(upb_Arena* a, size_t init_capacity,
                                     int elem_size_lg2) {
  UPB_ASSERT(elem_size_lg2 != 1);
  UPB_ASSERT(elem_size_lg2 <= 4);
  const size_t arr_size = UPB_ALIGN_UP(sizeof(upb_Array), UPB_MALLOC_ALIGN);
  const size_t bytes = arr_size + (init_capacity << elem_size_lg2);
  upb_Array* arr = (upb_Array*)upb_Arena_Malloc(a, bytes);
  if (!arr) return NULL;
  _upb_Array_SetTaggedPtr(arr, UPB_PTR_AT(arr, arr_size, void), elem_size_lg2);
  arr->size = 0;
  arr->capacity = init_capacity;
  return arr;
}

// Resizes the capacity of the array to be at least min_size.
bool _upb_array_realloc(upb_Array* arr, size_t min_size, upb_Arena* arena);

UPB_INLINE bool _upb_array_reserve(upb_Array* arr, size_t size,
                                   upb_Arena* arena) {
  if (arr->capacity < size) return _upb_array_realloc(arr, size, arena);
  return true;
}

// Resize without initializing new elements.
UPB_INLINE bool _upb_Array_ResizeUninitialized(upb_Array* arr, size_t size,
                                               upb_Arena* arena) {
  UPB_ASSERT(size <= arr->size || arena);  // Allow NULL arena when shrinking.
  if (!_upb_array_reserve(arr, size, arena)) return false;
  arr->size = size;
  return true;
}

// This function is intended for situations where elem_size is compile-time
// constant or a known expression of the form (1 << lg2), so that the expression
// i*elem_size does not result in an actual multiplication.
UPB_INLINE void _upb_Array_Set(upb_Array* arr, size_t i, const void* data,
                               size_t elem_size) {
  UPB_ASSERT(i < arr->size);
  UPB_ASSERT(elem_size == 1U << _upb_Array_ElemSizeLg2(arr));
  char* arr_data = (char*)_upb_array_ptr(arr);
  memcpy(arr_data + (i * elem_size), data, elem_size);
}

UPB_INLINE void _upb_array_detach(const void* msg, size_t ofs) {
  *UPB_PTR_AT(msg, ofs, upb_Array*) = NULL;
}

#ifdef __cplusplus
} /* extern "C" */
#endif

#undef _UPB_ARRAY_MASK_IMM
#undef _UPB_ARRAY_MASK_LG2
#undef _UPB_ARRAY_MASK_ALL

#include "upb/port/undef.inc"

#endif /* UPB_MESSAGE_INTERNAL_ARRAY_H_ */