Unum (number format)
Unums (universal numbers[1]) are a family of number formats and arithmetic for implementing real numbers on a computer, proposed by John L. Gustafson in 2015.[2] They are designed as an alternative to the ubiquitous IEEE 754 floating-point standard. The latest version is known as posits.[3]
The first version of unums, formally known as Type I unum, was introduced in Gustafson's book The End of Error as a superset of the IEEE-754 floating-point format.[2] The defining features of the Type I unum format are:
For computation with the format, Gustafson proposed using interval arithmetic with a pair of unums, what he called a ubound, providing the guarantee that the resulting interval contains the exact solution.
In February 2017, Gustafson officially introduced Type III unums, posits for fixed floating-point-like values and valids for interval arithmetic.[3] In March 2021, a standard was ratified and published by the Posit Working Group.[9]
