[kens]

I've been looking at the 8087 NaN circuitry lately. Having 2^53 (or whatever) values for NaN was supposedly a feature: "the large number of NAN values that are available, provide the sophisticated programmer with a tool that can be applied to a variety of special situations." For example, the different NaN values could hold debugging information to track down errors.

See "8087 Numeric Data Processor" page S-74: https://ethw.org/w/images/2/2f/Intel_8086_family_users_numer...

[TomatoCo]

You'll see some scripting languages (ab)use this. Where the native "number" type is a 64 bit float and only one NaN bit pattern is a real NaN. The others smuggle a pointer to an object in the lower bits. This way you don't spend any memory overhead indicating if a given variable contains a primitive or an object.

[adgjlsfhk1]

> For example, the different NaN values could hold debugging information to track down errors.

Unfortunately IEEE didn't bother specifying NaN propagation semantics so it ended up pretty useless.