microsoft / same-ish

A Clojure library for approximate comparison of floating point types in tests

same/ish - floating point comparisons for tests.

Equality may perhaps be a right, but no power on earth can ever turn it into a fact.
        — Honore de Balzac

You have some functions that return doubles or floats and you want to write some tests. How do you compare your results to the expected values? You can't use equality because of rounding errors, so you have to check if the values are near each other. But how near is near enough? And what if your numbers are buried inside data structures?

same/ish is designed to help with these situations.

Usage

See the full API docs are available on cljdoc for more detailed instructions and examples. A brief summary is provided below.

In Leiningen, add the following to your :dependencies in project.clj:

Then in your test namespace(s), require same.core:

(ns foo-test
  (:requre [clojure.test :refer :all]
           [same.core :refer [ish? zeroish?]]))

To compare two numbers, instead of using = or ==, use ish?:

(defn f [x]
  (* (/ 1. x) x)))

(deftest f-test
  (is (ish? 1.0 (f 49.0))))

You can also compare data structures, and they will be compared element-wise, using ish? for floating point types, == for other numbers, and = for anything else:

(defn g [x]
  {:a x
   :b [(* x x) (Math/sqrt x)]))

(deftest g-test
  (is (ish? {:a 23 :b [529 4.7958315233]}
            (g 23.0))))

Requirements

Clojure 1.7.0 or higher is required due to the reader conditionals required for ClojureScript support.

References

• Comparing Floating Point Numbers, 2012 Edition
• What Every Computer Scientist Should Know About Floating-Point Arithmetic
• Floating Point Demystified, Part 1
• Floating Point Demystified, Part 2

Changelog

See CHANGELOG.md.

Contributing

Contributions are welcomed, see CONTRIBUTING.md for details.

License

Copyright © Microsoft Corporation. All rights reserved.
Licensed under the MIT License.

same-ish's Issues

This repo is missing important files

There are important files that Microsoft projects should all have that are not present in this repository. A pull request has been opened to add the missing file(s). When the pr is merged this issue will be closed automatically.

Microsoft teams can learn more about this effort and share feedback within the open source guidance available internally.

Merge this pull request

Negative numbers are all zeroish?

  (require '[same :as same])
  (same/zeroish? 0) ;; true
  (same/zeroish? 1) ;; false
  (same/zeroish? -1) ;; true
  (same/zeroish? -100) ;; true

Very close number not ish?

I am not understanding a lot on floating points, but it seems to me that these
2 should be "equal" for ish?:

(ish? 1798.4039776258396
         1798.4039776258326)

but they are not.

Clojurescript support

Shouldn't be too hard to make it support Clojurescript as well as JVM Clojure