关于数据流的crc32功能说明 [英] crc32 function explanation with regards to data streams

问题描述

在哪里可以找到此crc32()函数的详细信息?我看到了这个链接，但我不知道CRC是如何正在计算.我问了一个有关基于数据流更新CRC而不是等待拥有所有数据的问题.我得到的答案如下(感谢@MarkAdler):

Where I can find this crc32() function in detail? I saw this Link but I couldn't figure out how CRC is being calculated. I asked a question about updating the CRC based on the data stream instead of waiting to have all the data. I got the answer as follows (Thanks to @MarkAdler):

unsigned long crc = crc32(0, NULL, 0);    // initial CRC
for (...) {                               // some sort of loop
    ...                                   // generating a chunk of data
    crc = crc32(crc, buf, len);           // update the CRC with the data
    ...                                   // this all gets repeated many times
}
...                                       // loop is done, crc has the CRC

1. 能否请您更详细地介绍 crc32()函数?
2. 该函数是否有任何伪代码可以解释它?
3. 这里的 for 循环是为了正确获取数据?

1. Can you please be more specific about the crc32() function?
2. Is there any pseudo code for that function which explains it?
3. And for loop here is for getting data right?

谢谢

推荐答案

1. 具体如何?
2. 您想解释一下如何使用它，或如何在内部使用它吗?它在内部的工作方式在您链接的源代码中.
3. 是的.您可以从任何地方获取数据块，然后通过 crc32()馈送它们，以获取整个数据流的CRC-32/ISO-HDLC.

1. More specific how?
2. Do you want an explanation of how to use it, or how it works internally? How it works internally is in the source code you linked.
3. Yes. You would get chunks of data from wherever, and feed them through crc32() to get the CRC-32/ISO-HDLC of the entire stream of data.

至于您链接的源代码，并不是为了告诉任何人有关CRC的工作原理而编写的.它写得很快.这是C语言中一个简单但缓慢(每次一次)的CRC例程，可能会或可能不会帮助您找到所需的内容:

As for the source code you linked, that was not written to teach anyone about how CRC's work. It was written to be fast. Here is a simple, but slow (one bit at a time), CRC routine in C, that may, or may not, help you with what you're looking for:

uint32_t crc32iso_hdlc_bit(uint32_t crc, void const *mem, size_t len) {
    unsigned char const *data = mem;
    if (data == NULL)
        return 0;
    crc = ~crc;
    for (size_t i = 0; i < len; i++) {
        crc ^= data[i];
        for (unsigned k = 0; k < 8; k++) {
            crc = crc & 1 ? (crc >> 1) ^ 0xedb88320 : crc >> 1;
        }
    }
    crc = ~crc;
    return crc;
}

(该代码由 crcany 生成.)

如果您想了解有关CRC的更多信息，请在此处开始.

If you would like to learn more about CRCs, start here.

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