ldpc的编解码，压缩文件有密码 源码重复或已经存在 -ldpc encoding and LDPC decoding，Compressed files have passwords，Source repeated or already exists

LDPC编码中的BP算法，已知校验阵H,先验证是否有4环，并实现随机生成信息序列编码并解码。-BP LDPC coding algorithm, known check matrix H, first verify whether there are four rings, and to achieve a randomly generated sequence information encoding and decoding.