函数 av_sha512_init 

pub unsafe extern "C" fn av_sha512_init(
    context: *mut AVSHA512,
    bits: c_int,
) -> c_int

Initialize SHA-2 512 hashing.

@param context pointer to the function context (of size av_sha512_size) @param bits number of bits in digest (224, 256, 384 or 512 bits) @return zero if initialization succeeded, -1 otherwise