private static void incrementalCopy(byte[] src, int srcIndex, byte[] op, int opIndex, int length) {
        do {
            op[opIndex++] = src[srcIndex++];
        } while (--length > 0);
    }
Copy "len" bytes from "src" to "op", one byte at a time.  Used for
handling COPY operations where the input and output regions may
overlap.  For example, suppose:
src    == "ab"
op     == src + 2
len    == 20
<p>
After incrementalCopy, the result will have
eleven copies of "ab"
ababababababababababab
Note that this does not match the semantics of either memcpy()
or memmove().
codec/codec-api/src/main/java/com/alipay/sofa/rpc/codec/snappy/SnappyDecompressor.java