snappy算法的详细解析

1. 获取原始数据大小N，将N存储到输出结果开头位置，占用1-5个字节不等：

• N < (1 << 7)时，占1个字节

out[0] = N

• N < (1 << 14)时，占2个字节

out[0] = N | 128; out[1] = N >> 7;

• N < (1 << 21)时，占3个字节

out[0] = N | 128; out[1] = (N >> 7) | 128; out[2] = N >> 14;

• N < (1 << 28)时，占4个字节

out[0] = N | 128; out[1] = (N >> 7) | 128; out[2] = (N >> 14) | 128; out[3] = N >> 21;

• other
  out[0] = N | 128; out[1] = (N >> 7) | 128; out[2] = (N >> 14) | 128; out[3] = (N >> 21) | 128; out[4] = N >> 28;

2. 将数据切分为65536字节的块，循环处理各个块

（1）建立一个类型定义为uint16的哈希表，并将其初始值设为零；

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