Posits: the good, the bad and the ugly

Many properties of the IEEE-754 floating-point number system are taken for granted in modern computers and are deeply embedded in compilers and low-level software routines such as elementary functions or BLAS. This article reviews such properties on the posit number system. Some are still true. Some are no longer true, but sensible work-arounds are possible, and even represent exciting challenges for the community. Some represent a danger if posits are to replace floating point completely. This study helps framing where posits are better than floating-point, where they are worse, what is the cost of posit hardware, and what tools are missing in the posit landscape. For general-purpose computing, using posits as a storage format could be a way to reap their benefits without losing those of classical floating-point.