Part of what you wish were true is already true: Using = to compare a double to a BigDecimal always returns false in Clojure, as does comparing a float to a BigDecimal.
It is only (= float-value double-value) that can return true in Clojure, even though hash does not guarantee the usual hash consistency property of "(= a b) implies (= (hash a) (hash b))". Hence my recommendation earlier in the thread to avoid mixing floats and doubles in the same Clojure program. Andy On Thu, Jan 22, 2015 at 2:04 PM, Fluid Dynamics <a2093...@trbvm.com> wrote: > On Thursday, January 22, 2015 at 2:12:52 PM UTC-5, Jozef Wagner wrote: >> >> As seen in CLJ-1372, this issue will probably cause some strong opinions. >> I think this is an example of a leaky abstraction and the current approach >> is to leave it as is, as there are some serious trade-offs and are there is >> no rationale or real practical reason to fix this. >> >> Current implementation for double and float hashes uses Java's hash >> algorithm, which >> uses IEEE 754 bit representation of floats, that is a fast native >> function [1], but is different for doubles and floats. While Murmur3 does >> provide hashing for integer numbers, there is no hash function for floating >> point ones. >> >> And note that there are big decimals too... >> >> > (hash 1.5) >> 1073217536 >> > (hash 1.5M) >> 466 >> > (hash (float 1.5)) >> 1069547520 >> > > Things that don't have the same hash shouldn't compare equal, at least so > long as one avoids mutable java.util collections. > > If floats and doubles can't generally have the same hashes (let alone > floats and BigDecimals) then = should return false for any comparison of > two different of these three types (and numerical code that wants to check > for numerical equality across types, to the extent that ever makes sense > with FP types, should use ==). > > -- > You received this message because you are subscribed to the Google > Groups "Clojure" group. > To post to this group, send email to clojure@googlegroups.com > Note that posts from new members are moderated - please be patient with > your first post. > To unsubscribe from this group, send email to > clojure+unsubscr...@googlegroups.com > For more options, visit this group at > http://groups.google.com/group/clojure?hl=en > --- > You received this message because you are subscribed to the Google Groups > "Clojure" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to clojure+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en --- You received this message because you are subscribed to the Google Groups "Clojure" group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
