There are two ways to encode a repeated field (100 floats, but could also be any size up to the limits of repeteating fields): "Ordinary (not packed) repeated fields emit one record for every element of the field." That means type, value, type, value, etc"

However, "packed" fields are exactly a length followed by a byte array of the typed data. This was an oversight in original proto2 which is unlikely to be corrected, but packed the default in proto3.