fast_crc.hpp

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#pragma once
 
#include <array>
#include <cstdint>
#include <fstream>
#include <iostream>
#include <string>

class FastCrc {
 public:
  static constexpr uint32_t POLY = 0x4C11DB7;
  static constexpr size_t DEFAULT_SIZE = 0x08080000 - 0x08008000;
  static constexpr size_t BIT_IN_BYTE = 8;
  static constexpr int UINT32_BIT_COUNT = 32;
  static constexpr int TOP_BYTE_SHIFT = 24;
  static constexpr uint32_t BYTE_MASK = 0xFF;
  static auto set_crc32_init_value(const uint32_t start) -> uint32_t {
    uint32_t init = 0;
 
    if (start != 0U) {
      int val = UINT32_BIT_COUNT;
      while (val != 0) {
        val -= BIT_IN_BYTE;
        const uint32_t byte = start >> val & 0xFF;
        // ReSharper disable once CppRedundantParentheses
        init = CRC32_TABLE[init >> TOP_BYTE_SHIFT ^ (byte & BYTE_MASK)] ^
               init << BIT_IN_BYTE;
      }
    }
    return init;
  }
 
  static auto fast_crc32(uint32_t sum, const unsigned char* ptr, uint32_t len)
      -> uint32_t {
    while (len-- != 0U) {
      const size_t index = sum >> 24 ^ *ptr++;
      sum = CRC32_TABLE[index] ^ sum << BIT_IN_BYTE;
    }
    return sum;
  }
 
  static auto check_app_valid(const std::string_view file_path) -> bool {
    std::ifstream content{std::string(file_path)};
    if (!content) {
      std::cerr << "Failed to open file: " << file_path << '\n';
      return false;
    }
    content.seekg(0, std::ios::end);
    const size_t size = content.tellg();
    content.seekg(0, std::ios::beg);
    if (size < 4) {
      std::cerr << "File too small to contain CRC: " << file_path << '\n';
      return false;
    }
    auto* const buffer = new char[size];
    content.read(buffer, static_cast<int>(size));
    if (!content) {
      std::cerr << "Failed to read file: " << file_path << '\n';
      delete[] buffer;
      return false;
    }
    const bool result = check(buffer, size);
    delete[] buffer;
    return result;
  }
 
  // Первое слово из всех единиц — область flash-памяти ещё не была записана.
  static constexpr uint32_t ERASED_FLASH_MARKER = 0xFFFFFFFF;
 
  static auto check(char* base, const uint32_t size = DEFAULT_SIZE) -> bool {
    if (*reinterpret_cast<uint32_t*>(base) == ERASED_FLASH_MARKER) {
      return false;
    }
    uint32_t csum = set_crc32_init_value(0x00000000);
    csum = fast_crc32(csum, reinterpret_cast<unsigned char*>(base), size - 4);
    const uint32_t wrote_crc = *reinterpret_cast<uint32_t*>(base + size - 4);
 
    return csum == wrote_crc;
  }
 
 private:
  static constexpr std::array<uint32_t, 256> CRC32_TABLE = {
      0x00000000, 0x04c11db7, 0x09823b6e, 0x0d4326d9, 0x130476dc, 0x17c56b6b,
      0x1a864db2, 0x1e475005, 0x2608edb8, 0x22c9f00f, 0x2f8ad6d6, 0x2b4bcb61,
      0x350c9b64, 0x31cd86d3, 0x3c8ea00a, 0x384fbdbd, 0x4c11db70, 0x48d0c6c7,
      0x4593e01e, 0x4152fda9, 0x5f15adac, 0x5bd4b01b, 0x569796c2, 0x52568b75,
      0x6a1936c8, 0x6ed82b7f, 0x639b0da6, 0x675a1011, 0x791d4014, 0x7ddc5da3,
      0x709f7b7a, 0x745e66cd, 0x9823b6e0, 0x9ce2ab57, 0x91a18d8e, 0x95609039,
      0x8b27c03c, 0x8fe6dd8b, 0x82a5fb52, 0x8664e6e5, 0xbe2b5b58, 0xbaea46ef,
      0xb7a96036, 0xb3687d81, 0xad2f2d84, 0xa9ee3033, 0xa4ad16ea, 0xa06c0b5d,
      0xd4326d90, 0xd0f37027, 0xddb056fe, 0xd9714b49, 0xc7361b4c, 0xc3f706fb,
      0xceb42022, 0xca753d95, 0xf23a8028, 0xf6fb9d9f, 0xfbb8bb46, 0xff79a6f1,
      0xe13ef6f4, 0xe5ffeb43, 0xe8bccd9a, 0xec7dd02d, 0x34867077, 0x30476dc0,
      0x3d044b19, 0x39c556ae, 0x278206ab, 0x23431b1c, 0x2e003dc5, 0x2ac12072,
      0x128e9dcf, 0x164f8078, 0x1b0ca6a1, 0x1fcdbb16, 0x018aeb13, 0x054bf6a4,
      0x0808d07d, 0x0cc9cdca, 0x7897ab07, 0x7c56b6b0, 0x71159069, 0x75d48dde,
      0x6b93dddb, 0x6f52c06c, 0x6211e6b5, 0x66d0fb02, 0x5e9f46bf, 0x5a5e5b08,
      0x571d7dd1, 0x53dc6066, 0x4d9b3063, 0x495a2dd4, 0x44190b0d, 0x40d816ba,
      0xaca5c697, 0xa864db20, 0xa527fdf9, 0xa1e6e04e, 0xbfa1b04b, 0xbb60adfc,
      0xb6238b25, 0xb2e29692, 0x8aad2b2f, 0x8e6c3698, 0x832f1041, 0x87ee0df6,
      0x99a95df3, 0x9d684044, 0x902b669d, 0x94ea7b2a, 0xe0b41de7, 0xe4750050,
      0xe9362689, 0xedf73b3e, 0xf3b06b3b, 0xf771768c, 0xfa325055, 0xfef34de2,
      0xc6bcf05f, 0xc27dede8, 0xcf3ecb31, 0xcbffd686, 0xd5b88683, 0xd1799b34,
      0xdc3abded, 0xd8fba05a, 0x690ce0ee, 0x6dcdfd59, 0x608edb80, 0x644fc637,
      0x7a089632, 0x7ec98b85, 0x738aad5c, 0x774bb0eb, 0x4f040d56, 0x4bc510e1,
      0x46863638, 0x42472b8f, 0x5c007b8a, 0x58c1663d, 0x558240e4, 0x51435d53,
      0x251d3b9e, 0x21dc2629, 0x2c9f00f0, 0x285e1d47, 0x36194d42, 0x32d850f5,
      0x3f9b762c, 0x3b5a6b9b, 0x0315d626, 0x07d4cb91, 0x0a97ed48, 0x0e56f0ff,
      0x1011a0fa, 0x14d0bd4d, 0x19939b94, 0x1d528623, 0xf12f560e, 0xf5ee4bb9,
      0xf8ad6d60, 0xfc6c70d7, 0xe22b20d2, 0xe6ea3d65, 0xeba91bbc, 0xef68060b,
      0xd727bbb6, 0xd3e6a601, 0xdea580d8, 0xda649d6f, 0xc423cd6a, 0xc0e2d0dd,
      0xcda1f604, 0xc960ebb3, 0xbd3e8d7e, 0xb9ff90c9, 0xb4bcb610, 0xb07daba7,
      0xae3afba2, 0xaafbe615, 0xa7b8c0cc, 0xa379dd7b, 0x9b3660c6, 0x9ff77d71,
      0x92b45ba8, 0x9675461f, 0x8832161a, 0x8cf30bad, 0x81b02d74, 0x857130c3,
      0x5d8a9099, 0x594b8d2e, 0x5408abf7, 0x50c9b640, 0x4e8ee645, 0x4a4ffbf2,
      0x470cdd2b, 0x43cdc09c, 0x7b827d21, 0x7f436096, 0x7200464f, 0x76c15bf8,
      0x68860bfd, 0x6c47164a, 0x61043093, 0x65c52d24, 0x119b4be9, 0x155a565e,
      0x18197087, 0x1cd86d30, 0x029f3d35, 0x065e2082, 0x0b1d065b, 0x0fdc1bec,
      0x3793a651, 0x3352bbe6, 0x3e119d3f, 0x3ad08088, 0x2497d08d, 0x2056cd3a,
      0x2d15ebe3, 0x29d4f654, 0xc5a92679, 0xc1683bce, 0xcc2b1d17, 0xc8ea00a0,
      0xd6ad50a5, 0xd26c4d12, 0xdf2f6bcb, 0xdbee767c, 0xe3a1cbc1, 0xe760d676,
      0xea23f0af, 0xeee2ed18, 0xf0a5bd1d, 0xf464a0aa, 0xf9278673, 0xfde69bc4,
      0x89b8fd09, 0x8d79e0be, 0x803ac667, 0x84fbdbd0, 0x9abc8bd5, 0x9e7d9662,
      0x933eb0bb, 0x97ffad0c, 0xafb010b1, 0xab710d06, 0xa6322bdf, 0xa2f33668,
      0xbcb4666d, 0xb8757bda, 0xb5365d03, 0xb1f740b4};
};