sha256_ctx2hash((sha256_hash_t*)dest, &(s->a));
sha256_lastBlock(&(s->b), dest, SHA256_HASH_BITS);
sha256_ctx2hash((sha256_hash_t*)dest, &(s->b));
sha256_ctx2hash((sha256_hash_t*)dest, &(s->a));
sha256_lastBlock(&(s->b), dest, SHA256_HASH_BITS);
sha256_ctx2hash((sha256_hash_t*)dest, &(s->b));