ExperimentalHypothesis · December 5, 2019 09:30 · Oct 10, 2017
diff --git a/sha256.cpp b/sha256.cpp
@@ -0,0 +1,89 @@
+// -*- coding:utf-8; mode:c++; mode:auto-fill; fill-column:80; -*-
+
+/// @file      sha256.cpp
+/// @brief     Calculate and display the SHA-256 hash of a list of files.
+/// @author    J. Arrieta <[email protected]>
+/// @date      October 10, 2017
+/// @copyright (c) 2017 Nabla Zero Labs
+/// @license   MIT License
+///
+/// Compiled in macOS High Sierra 10.13 (previous installation of OpenSSL 1.1.0).
+///
+///     $ clang++ sha256.cpp -osha256 -std=c++1z -Wall -Wextra -march=native \
+///       -Ofast -lssl -lcrypto
+///     $ ./sha256
+///       usage: ./sha256 FILE_1 [FILE_2 [... [FILE_N]]]
+///     $ ./sha256 sha256
+///       f4774d172b9177109045759ada55f55a47a602c0b0392330d5c4b79e9d474fb0 sha256
+///
+
+// C++ Standard Library
+#include <cstdlib>
+#include <cerrno>
+#include <cstring>
+#include <fstream>
+#include <iostream>
+#include <iomanip>
+#include <sstream>
+#include <string>
+#include <stdexcept>
+
+// OpenSSL Library
+#include <openssl/sha.h>
+
+inline std::string
+SHA256(const char* const path)
+{
+  std::ifstream fp(path, std::ios::in | std::ios::binary);
+
+  if (not fp.good()) {
+    std::ostringstream os;
+    os << "Cannot open \"" << path << "\": " << std::strerror(errno) << ".";
+    throw std::runtime_error(os.str());
+  }
+
+  constexpr const std::size_t buffer_size { 1 << 12 };
+  char buffer[buffer_size];
+
+  unsigned char hash[SHA256_DIGEST_LENGTH] = { 0 };
+
+  SHA256_CTX ctx;
+  SHA256_Init(&ctx);
+
+  while (fp.good()) {
+    fp.read(buffer, buffer_size);
+    SHA256_Update(&ctx, buffer, fp.gcount());
+  }
+
+  SHA256_Final(hash, &ctx);
+  fp.close();
+
+  std::ostringstream os;
+  os << std::hex << std::setfill('0');
+
+  for (int i = 0; i < SHA256_DIGEST_LENGTH; ++i) {
+    os << std::setw(2) << static_cast<unsigned int>(hash[i]);
+  }
+
+  return os.str();
+}
+
+int
+main(int argc, char* argv[])
+{
+
+  if (argc < 2) {
+    std::cerr << "usage: " << argv[0] << " FILE_1 [FILE_2 [... [FILE_N]]]" << std::endl;
+    return EXIT_FAILURE;
+  }
+
+  for (int arg = 1; arg < argc; ++arg) {
+    try {
+      std::cout << SHA256(argv[arg]) << " " << argv[arg] << std::endl;
+    } catch(const std::exception& e) {
+      std::cerr << "[fatal] " <<  e.what() << std::endl;
+    }
+  }
+
+  return EXIT_SUCCESS;
+}
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