Algorismus is a branch of Medieval mathematics that deals with the earliest European introduction of the Hindu-Arabic number system. The name represents the latinification of the name of a Persian author Al-Khwarizmi , who had written a book on this new method of reckoning with numbers in Arabic. When Al Khwarizmi's writings became available in Latin translations and digests, it started a revolution in numerical mathematics. The modern term algorithm has been adapted from this Latin word.
Well known early Latin texts on this topic are Alexander de Villa Dei's Carmen de Algorismo, i.e. the Song on Algorismus and Johannes de Sacrobosco's treatise Tractatus De Arte Numerandi - Tract on the Art of Numbering.