Pretty much all Dichlor you get in pool stores is the dihydrate that has 55% Available Chlorine (pure Dichlor dihydrate would be 55.4%, but product is usually around 99% pure). The anhydrous form of Dichlor (if pure) has 64.5% Available Chlorine but it's not normally sold because as shown in this post, the anhydrous Dichlor is a Class 3 oxidizer similar to Cal-Hypo at > 50% concentration while the dihydrate is a Class 1 oxidizer similar to Trichlor. So to avoid the additional storage, shipping, and warning requirements associated with a Class 3 oxidizer, the dihydrate form is pretty much the only one sold for pools and spas.

So Carl's calculation is correct that 1 pound of Dichlor (dihydrate) in 10,000 gallons would yield 6.6 ppm FC and 6.0 ppm CYA.