checksum.cpp

/*
 *     .============.
 *    //  M A K E  / \
 *   //  C++ DEV  /   \
 *  //  E A S Y  /  \/ \
 * ++ ----------.  \/\  .
 *  \\     \     \ /\  /
 *   \\     \     \   /
 *    \\     \     \ /
 *     -============'
 *
 * Copyright (c) 2018 Hevake and contributors, all rights reserved.
 *
 * This file is part of cpp-tbox (https://github.com/cpp-main/cpp-tbox)
 * Use of this source code is governed by MIT license that can be found
 * in the LICENSE file in the root of the source tree. All contributing
 * project authors may be found in the CONTRIBUTORS.md file in the root
 * of the source tree.
 */
#include "checksum.h"

namespace tbox {
namespace util {

uint8_t CalcCheckSum8(const void *data_ptr, size_t data_size)
{
    const uint8_t *byte_ptr = (const uint8_t *)data_ptr;
    uint16_t acc = 0;

    for (size_t i = 0; i < data_size; ++i) {
        acc += byte_ptr[i];
        while ((acc & 0xff00) != 0)
            acc = (acc & 0xff) + (acc >> 8);
    }

    return ~((uint8_t)acc);
}

uint16_t CalcCheckSum16(const void *data_ptr, size_t data_size)
{
    uint32_t acc = 0;

    if (data_size > 0) {
        uint8_t *bytes = (uint8_t*)data_ptr;

        while (data_size > 1) {
            acc += (bytes[0] << 8 | bytes[1]);
            while ((acc & 0xffff0000UL) != 0)
                acc = (acc >> 16) + (acc & 0x0000ffffUL);

            bytes += 2;
            data_size -= 2;
        }

        if (data_size > 0) {
            acc += (bytes[0] << 8);
            while ((acc & 0xffff0000UL) != 0)
                acc = (acc >> 16) + (acc & 0x0000ffffUL);
        }
    }

    uint16_t ret = (uint16_t)acc;
    return ~ret;
}

}
}