File 1048-doc-Better-description-of-problems-with-fl... of Package erlang

Overview Repositories Revisions Requests Users Attributes Meta

File 1048-doc-Better-description-of-problems-with-float-repres.patch of Package erlang (Revision b921e8aed3aceafaa8c09c18784302db)

Currently displaying revision b921e8aed3aceafaa8c09c18784302db , Show latest

From c70b2f1eb555087798092500d0dc4495c4c929df Mon Sep 17 00:00:00 2001
From: Kjell Winblad <kjellwinblad@gmail.com>
Date: Thu, 1 Oct 2020 11:57:52 +0200
Subject: [PATCH 38/39] doc: Better description of problems with float
 representation

Co-authored-by: Lucas Larsson <garazdawi@gmail.com>
Co-authored-by: Hans Bolinder <hasse@erlang.org>
---
 erts/doc/src/erlang.xml                    | 10 +++--
 system/doc/reference_manual/data_types.xml | 43 ++++++++++++----------
 2 files changed, 30 insertions(+), 23 deletions(-)

diff --git a/erts/doc/src/erlang.xml b/erts/doc/src/erlang.xml
index bef39344c2..db3303c0a5 100644
--- a/erts/doc/src/erlang.xml
+++ b/erts/doc/src/erlang.xml
@@ -1996,10 +1996,12 @@ true</pre>
 "7.12"
 > <input>float_to_list(7.12, [{scientific, 3}]).</input>
 "7.120e+00"
-> <input>float_to_list(0.1+0.2)</input></pre>
+> <input>float_to_list(0.1+0.2)</input>
+"3.00000000000000044409e-01"
+</pre>
 <p>In the last example, <c>float_to_list(0.1+0.2)</c> evaluates to
 <c>"3.00000000000000044409e-01"</c>. The reason for this is that
-<seealso marker="system/reference_manual:data_types#float_represenation_problem"><c>0.1</c> and
+<seealso marker="system/reference_manual:data_types#float_representation_problem"><c>0.1</c> and
 <c>0.2</c> cannot be represented exactly as float
 values</seealso>.</p>
       </desc>
@@ -6359,7 +6361,7 @@ true</pre>
       <p>In the last example, <c>round(36028797018963969.0)</c>
       evaluates to <c>36028797018963968</c>. The reason for this is
       that <seealso
-      marker="system/reference_manual:data_types#float_represenation_problem"><c>36028797018963969.0</c>
+      marker="system/reference_manual:data_types#float_representation_problem"><c>36028797018963969.0</c>
       cannot be represented exactly as a float value</seealso>.</p>
         <p>Allowed in guard tests.</p>
       </desc>
@@ -12127,7 +12129,7 @@ improper_end</pre>
 36028797018963968</pre>
 <p>In the last example, <c>trunc(36028797018963969.0)</c> evaluates to
 <c>36028797018963968</c>. The reason for this is that <seealso
-marker="system/reference_manual:data_types#float_represenation_problem"><c>36028797018963969.0</c>
+marker="system/reference_manual:data_types#float_representation_problem"><c>36028797018963969.0</c>
 cannot be represented exactly as a float value</seealso>.</p>
         <p>Allowed in guard tests.</p>
       </desc>
diff --git a/system/doc/reference_manual/data_types.xml b/system/doc/reference_manual/data_types.xml
index b3f1162209..f3a85df39b 100644
--- a/system/doc/reference_manual/data_types.xml
+++ b/system/doc/reference_manual/data_types.xml
@@ -70,25 +70,30 @@
 2.3e3
 8> <input>2.3e-3.</input>
 0.0023</pre>
-<marker id="float_represenation_problem" /><note>
-  <p>Float literals cannot always be
-  represented exactly as floats. This is due to the fact that floats
-  are represented by a fixed number of bits in a base-2 system while
-  float literals are represented with a base-10 system. Here are
-  examples of this phenomenon:</p>
-  <pre>
-    > <input>0.1+0.2.</input>
-    0.30000000000000004
-    > <input>36028797018963969.0.</input>
-    36028797018963970.0
-  </pre>
-  <p>See external resources for a detailed description of why this is
-  the case (for example <url
-  href="https://floating-point-gui.de/">https://floating-point-gui.de/</url>
-  and <url
-  href="https://0.30000000000000004.com/">https://0.30000000000000004.com/</url>)</p>
-</note>
-
+<marker id="float_representation_problem" />
+    <section>
+      <title>Representation of Floating Point Numbers</title>
+      <p>When working with floats you may not see what you expect when printing or
+        doing arithmetic operations. This is because floats
+        are represented by a fixed number of bits in a base-2 system while
+        printed floats are represented with a base-10 system. Here are
+        examples of this phenomenon:
+      </p>
+      <pre>
+> <input>0.1+0.2.</input>
+0.30000000000000004
+> <input>36028797018963969.0.</input>
+36028797018963970.0
+      </pre>
+      <p>For more information see <url href="https://floating-point-gui.de/">
+        What Every Programmer Should Know About Floating-Point Arithmetic</url>
+        and <url href="https://0.30000000000000004.com/">0.30000000000000004.com/</url>.
+      </p>
+      <p>If you need to work with decimal fractions, for instance if you need to represent money,
+        then you should use a library that handles that or work in cents instead of euros so
+        that you do not need decimal fractions.
+      </p>
+    </section>
   </section>
 
   <section>
-- 
2.26.2

Places

File 1048-doc-Better-description-of-problems-with-float-repres.patch of Package erlang (Revision b921e8aed3aceafaa8c09c18784302db)

Places