libc/src/__support/char_vector.h

   1 //===-- Standalone implementation of a char vector --------------*- C++ -*-===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #ifndef LLVM_LIBC_SRC_SUPPORT_CHARVECTOR_H
  10 #define LLVM_LIBC_SRC_SUPPORT_CHARVECTOR_H
  11
  12 #include "src/__support/common.h"
  13
  14 #include <stddef.h>
  15 #include <stdlib.h> // For allocation.
  16
  17 namespace __llvm_libc {
  18
  19 // This is very simple alternate of the std::string class. There is no
  20 // bounds check performed in any of the methods. The callers are expected to
  21 // do the checks before invoking the methods.
  22 //
  23 // This class will be extended as needed in future.
  24
  25 class CharVector {
  26   static constexpr size_t INIT_BUFF_SIZE = 64;
  27   char local_buffer[INIT_BUFF_SIZE];
  28   char *cur_str = local_buffer;
  29   size_t cur_buff_size = INIT_BUFF_SIZE;
  30   size_t index = 0;
  31
  32 public:
  33   CharVector() = default;
  34   LIBC_INLINE ~CharVector() {
  35     if (cur_str != local_buffer)
  36       free(cur_str);
  37   }
  38
  39   // append returns true on success and false on allocation failure.
  40   LIBC_INLINE bool append(char new_char) {
  41     // Subtract 1 for index starting at 0 and another for the null terminator.
  42     if (index >= cur_buff_size - 2) {
  43       // If the new character would cause the string to be longer than the
  44       // buffer's size, attempt to allocate a new buffer.
  45       cur_buff_size = cur_buff_size * 2;
  46       if (cur_str == local_buffer) {
  47         char *new_str;
  48         new_str = reinterpret_cast<char *>(malloc(cur_buff_size));
  49         if (new_str == NULL) {
  50           return false;
  51         }
  52         // TODO: replace with inline memcpy
  53         for (size_t i = 0; i < index; ++i)
  54           new_str[i] = cur_str[i];
  55         cur_str = new_str;
  56       } else {
  57         cur_str = reinterpret_cast<char *>(realloc(cur_str, cur_buff_size));
  58         if (cur_str == NULL) {
  59           return false;
  60         }
  61       }
  62     }
  63     cur_str[index] = new_char;
  64     ++index;
  65     return true;
  66   }
  67
  68   LIBC_INLINE char *c_str() {
  69     cur_str[index] = '\0';
  70     return cur_str;
  71   }
  72
  73   LIBC_INLINE size_t length() { return index; }
  74 };
  75
  76 } // namespace __llvm_libc
  77
  78 #endif // LLVM_LIBC_SRC_SUPPORT_CHARVECTOR_H