fix: suggested changes

Author: Md. Anisul Haque

hashing/sha256.cpp

@@ -31,28 +31,51 @@ namespace hashing {
  * algorithm implementation
  */
 namespace sha256 {
+/**
+ * @brief Computes size of the padded input
+ * @param input Input string
+ * @return size_t Size of the padded input
+ */
+std::size_t compute_padded_size(const std::size_t input_size) {
+    size_t padded_input_size = 0;
+    if (input_size % 64 < 56) {
+        padded_input_size = input_size + 64 - (input_size % 64);
+    } else {
+        padded_input_size = input_size + 128 - (input_size % 64);
+    }
+    return padded_input_size;
+}
+
+/**
+ * @brief Returns the byte at position byte_num in in_value
+ * @param in_value Input value
+ * @param byte_num Position of byte to be returned
+ * @return uint8_t Byte at position byte_num
+ */
+uint8_t extract_byte(const std::size_t in_value, const std::size_t byte_num) {
+    return ((in_value >> (byte_num * 8)) & 0xFF);
+}
+
 /**
  * @brief Returns the character at pos after the input is padded
  * @param input Input string
  * @param pos Position of character to be returned
- * @param padded_input_size Size of the padded input
  * @return char Character at the index pos in the padded string
  */
-char get_char(const std::string &input, std::size_t pos,
-              size_t padded_input_size) {
+char get_char(const std::string &input, std::size_t pos) {
     size_t input_size = input.length();
-    char ch = 0;
+    size_t padded_input_size = compute_padded_size(input_size);
     if (pos < input_size) {
-        ch = input[pos];
-    } else if (pos == input_size) {
-        ch = '\x80';
-    } else if (pos < padded_input_size - 8) {
-        ch = '\x00';
-    } else {
-        ch =
-            static_cast<char>((input_size * 8 >> (56 - (pos % 56) * 8)) & 0xFF);
+        return input[pos];
+    }
+    if (pos == input_size) {
+        return '\x80';
     }
-    return ch;
+    if (pos < padded_input_size - 8) {
+        return '\x00';
+    }
+    return static_cast<char>(
+        extract_byte(input_size * 8, padded_input_size - pos - 1));
 }
 
 /**
@@ -92,33 +115,22 @@ std::array<uint32_t, 8> compute_hash(const std::string &input) {
         0x5B9CCA4F, 0x682E6FF3, 0x748F82EE, 0x78A5636F, 0x84C87814, 0x8CC70208,
         0x90BEFFFA, 0xA4506CEB, 0xBEF9A3F7, 0xC67178F2};
 
-    size_t input_size = input.length();  // Input size in bytes
+    size_t input_size = input.length();  ///< Input size in bytes
 
-    // Calculate size of the padded input in bytes
-    size_t padded_input_size = 0;
-    if (input_size % 64 < 56) {
-        padded_input_size = input_size + 64 - (input_size % 64);
-    } else {
-        padded_input_size = input_size + 128 - (input_size % 64);
-    }
+    size_t padded_input_size =
+        compute_padded_size(input_size);  ///< Padded input size in bytes
 
     // Process message in successive 512-bit (64-byte) chunks
     for (size_t i = 0; i < padded_input_size; i += 64) {
         std::array<uint32_t, 64> blocks{};
 
         // Copy chunk into first 16 words of the message schedule array
         for (size_t j = 0; j < 16; ++j) {
-            blocks[j] = (static_cast<uint8_t>(
-                             get_char(input, i + j * 4, padded_input_size))
-                         << 24) |
-                        (static_cast<uint8_t>(
-                             get_char(input, i + j * 4 + 1, padded_input_size))
-                         << 16) |
-                        (static_cast<uint8_t>(
-                             get_char(input, i + j * 4 + 2, padded_input_size))
-                         << 8) |
-                        static_cast<uint8_t>(
-                            get_char(input, i + j * 4 + 3, padded_input_size));
+            blocks[j] =
+                (static_cast<uint8_t>(get_char(input, i + j * 4)) << 24) |
+                (static_cast<uint8_t>(get_char(input, i + j * 4 + 1)) << 16) |
+                (static_cast<uint8_t>(get_char(input, i + j * 4 + 2)) << 8) |
+                static_cast<uint8_t>(get_char(input, i + j * 4 + 3));
         }
 
         for (size_t j = 16; j < 64; ++j) {
@@ -185,7 +197,7 @@ std::string hash_to_string(const std::array<uint32_t, 8> &hash) {
     std::stringstream ss;
     for (size_t i = 0; i < 8; ++i) {
         for (size_t j = 0; j < 4; ++j) {
-            uint32_t byte = (hash[i] >> (24 - j * 8)) & 0xFF;
+            uint32_t byte = extract_byte(hash[i], 3 - j);
             ss << std::hex << std::setfill('0') << std::setw(2) << byte;
         }
     }
@@ -239,13 +251,5 @@ static void test() {
  */
 int main() {
     test();  // Run self-test implementations
-
-    // Custom Input
-    std::string input;
-    std::cout << "Enter a message to be hashed: ";
-    getline(std::cin, input);
-    std::string hash = hashing::sha256::sha256(input);
-    std::cout << "SHA-256 Hash: " << hash << std::endl;
-
     return 0;
 }