ref/deref traits导致这个有点奇葩的语法

use openssl::bn::BigNum;

let s = -BigNum::from_u32(12345).unwrap();
assert_eq!(&**s.to_dec_str().unwrap(), "-12345");

let little_big = BigNum::from_u32(std::u32::MAX)?;
assert_eq!(*&little_big.num_bytes(), 4);

https://docs.rs/openssl/0.10.12/openssl/bn/struct.BigNum.html#method.to_dec_str
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FROM 114.245.195.*