Theora

https://github.com/xiph/theora

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Theora is an open-source video compression format and codec developed by the Xiph.Org Foundation for...

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### CRC32 Generation Function (C)

Source: https://github.com/xiph/theora/blob/main/doc/draft-kerr-avt-theora-rtp-00.txt

C function that computes the CRC32 checksum for Theora Setup Headers. It uses the polynomial X^32+X^26+X^23+X^22+X^16+X^12+X^11+X^10+X^8+X^7+X^5+X^4+X^2+X^1+X^0. Implementations SHOULD use this function; if not, the CRC32 value MUST be generated using the same polynomial.

```c
unsigned int crc32 (int length, unsigned char *crcdata)
{
    int index, loop;
    unsigned int byte, crc, mask;

    index = 0;
    crc = 0xFFFFFFFF;

    while (index < length) {
        byte = crcdata [index];

        crc = crc ^ byte;

        for (loop = 7; loop >= 0; loop--) {
            mask = -(crc & 1);
            crc = (crc >> 1) ^ (0xEDB88320 & mask);
        }
        index++;
    }
    return ~crc;
}
```

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