a.setOffset(pack.length());
objectHeader(pack, Constants.OBJ_BLOB, base.length);
deflate(pack, base);
ByteArrayOutputStream tmp = new ByteArrayOutputStream();
DeltaEncoder de = new DeltaEncoder(tmp, base.length, 3L << 30);
de.copy(0, 1);
byte[] delta = tmp.toByteArray();
b.setOffset(pack.length());
objectHeader(pack, Constants.OBJ_REF_DELTA, delta.length);
idA.copyRawTo(pack);
deflate(pack, delta);