sha2 is much slower than crate ring on windows an linux

[zhuyu4839]

the source code:

src/aes256sha256.rs

line 143~156

        let mut sha = sha2::Sha256::default();
        let mut extra = [0u8; 8];
        for _ in 0..(1u32 << num_cycles_power) {
            sha.update(&salt);
            sha.update(password);
            sha.update(extra);
            for item in &mut extra {
                *item = item.wrapping_add(1);
                if *item != 0 {
                    break;
                }
            }
        }
        sha.finalize().into()

slow than use crate ring

        let mut sha = Context::new(&SHA256);
        let mut extra = [0u8; 8];
        for _ in 0..(1u32 << num_cycles_power) {
            sha.update(&salt);
            sha.update(password);
            sha.update(&extra);
            for item in &mut extra {
                *item = item.wrapping_add(1);
                if *item != 0 {
                    break;
                }
            }
        }
        sha.finish().as_ref().try_into()
            .map_err(|_| crate::Error::other("AES256 sha256 hashing failed"))?

[newpavlov]

See #327