Repository: TheAlgorithms/C-Plus-Plus
File: hashing/sha256.cpp (C++)

Code before:
 * @namespace hashing
 * @brief Hashing algorithms
 */
namespace hashing {
/**
 * @namespace SHA-256
 * @brief Functions for the [SHA-256](https://en.wikipedia.org/wiki/SHA-2)
 * algorithm implementation
 */
namespace sha256 {
/**
 * @brief Rotates the bits of a 32-bit unsigned integer
 * @param n Integer to rotate
 * @param rotate Number of bits to rotate
 * @return uint32_t The rotated integer
 */
uint32_t rightRotate(uint32_t n, size_t rotate) {
    return (n >> rotate) | (n << (32 - rotate));
}

/**
 * @brief The SHA-256 algorithm
 * @param input The input string to hash
 * @return std::string The final hash value
 */
std::string sha256(std::string &input) {
    // Initialize array of hash values with first 32 bits of the fractional
    // parts of the square roots of the first 8 primes 2..19
    uint32_t hash[8] = {0x6A09E667, 0xBB67AE85, 0x3C6EF372, 0xA54FF53A,
                        0x510E527F, 0x9B05688C, 0x1F83D9AB, 0x5BE0CD19};

    // Initialize array of round constants with first 32 bits of the fractional
    // parts of the cube roots of the first 64 primes 2..311
    const uint32_t k[64] = {
        0x428A2F98, 0x71374491, 0xB5C0FBCF, 0xE9B5DBA5, 0x3956C25B, 0x59F111F1,
        0x923F82A4, 0xAB1C5ED5, 0xD807AA98, 0x12835B01, 0x243185BE, 0x550C7DC3,
        0x72BE5D74, 0x80DEB1FE, 0x9BDC06A7, 0xC19BF174, 0xE49B69C1, 0xEFBE4786,
        0x0FC19DC6, 0x240CA1CC, 0x2DE92C6F, 0x4A7484AA, 0x5CB0A9DC, 0x76F988DA,
        0x983E5152, 0xA831C66D, 0xB00327C8, 0xBF597FC7, 0xC6E00BF3, 0xD5A79147,
        0x06CA6351, 0x14292967, 0x27B70A85, 0x2E1B2138, 0x4D2C6DFC, 0x53380D13,
        0x650A7354, 0x766A0ABB, 0x81C2C92E, 0x92722C85, 0xA2BFE8A1, 0xA81A664B,
        0xC24B8B70, 0xC76C51A3, 0xD192E819, 0xD6990624, 0xF40E3585, 0x106AA070,
        0x19A4C116, 0x1E376C08, 0x2748774C, 0x34B0BCB5, 0x391C0CB3, 0x4ED8AA4A,
        0x5B9CCA4F, 0x682E6FF3, 0x748F82EE, 0x78A5636F, 0x84C87814, 0x8CC70208,
        0x90BEFFFA, 0xA4506CEB, 0xBEF9A3F7, 0xC67178F2};

    // Pre-processing
    std::string padded_input = input;
    uint64_t input_size = input.length() * 8;  // Message length in bits

    // Append a single '1' bit

Review comment (suggestion):
```suggestion
std::string sha256(const std::string &input) {
```
`input` is not modified, so it should be `const`.

Code after:
#include <sstream>   /// For std::stringstream
#include <utility>   /// For std::move
#include <vector>    /// For std::vector

/**
 * @namespace hashing
 * @brief Hashing algorithms
 */
namespace hashing {
/**
 * @namespace SHA-256
 * @brief Functions for the [SHA-256](https://en.wikipedia.org/wiki/SHA-2)
 * algorithm implementation
 */
namespace sha256 {
/**
 * @class Hash
 * @brief Contains hash array and functions to update it and convert it to a
 * hexadecimal string
 */
class Hash {
    // Initialize array of hash values with first 32 bits of the fractional
    // parts of the square roots of the first 8 primes 2..19
    std::array<uint32_t, 8> hash = {0x6A09E667, 0xBB67AE85, 0x3C6EF372,
                                    0xA54FF53A, 0x510E527F, 0x9B05688C,
                                    0x1F83D9AB, 0x5BE0CD19};

 public:
    void update(const std::array<uint32_t, 64> &blocks);
    std::string to_string() const;
};

/**
 * @brief Rotates the bits of a 32-bit unsigned integer
 * @param n Integer to rotate
 * @param rotate Number of bits to rotate
 * @return uint32_t The rotated integer
 */
uint32_t right_rotate(uint32_t n, size_t rotate) {
    return (n >> rotate) | (n << (32 - rotate));
}

/**
 * @brief Updates the hash array
 * @param blocks Message schedule array
 * @return void
 */
void Hash::update(const std::array<uint32_t, 64> &blocks) {
    // Initialize array of round constants with first 32 bits of the fractional
    // parts of the cube roots of the first 64 primes 2..311
    const std::array<uint32_t, 64> round_constants = {