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File 5941-Efficiency-Guide-Add-more-examples-for-binaries.patch of Package erlang (Revision 940bcaab9cb548bf8f30d9bde2abe498)

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From 27645040e29aef98a3bb6f4862c067146973ef87 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Thu, 16 Mar 2023 10:27:31 +0100
Subject: [PATCH] Efficiency Guide: Add more examples for binaries

---
 .../doc/efficiency_guide/binaryhandling.xml   | 52 ++++++++++++++++++-
 1 file changed, 50 insertions(+), 2 deletions(-)

diff --git a/system/doc/efficiency_guide/binaryhandling.xml b/system/doc/efficiency_guide/binaryhandling.xml
index c0f7a36375..8cb7e7834b 100644
--- a/system/doc/efficiency_guide/binaryhandling.xml
+++ b/system/doc/efficiency_guide/binaryhandling.xml
@@ -32,7 +32,12 @@
 <file>binaryhandling.xml</file>
 </header>
 
- Binaries can be efficiently built in the following way:
+ This section gives a few examples on how to handle binaries in an
+ efficient way. The sections that follow take an in-depth look at how
+ binaries are implemented and how to best take advantages of the
+ optimizations done by the compiler and runtime system.
+
+ Binaries can be efficiently built in the following way:
 
 DO
 <code type="erl"><![CDATA[
@@ -44,7 +49,50 @@ my_list_to_binary([H|T], Acc) ->
 my_list_to_binary([], Acc) ->
 Acc.]]></code> 
 
- Binaries can be efficiently matched like this:
+ Appending data to a binary as in the example is efficient because
+ it is specially optimized by the runtime system to avoid copying the
+ <c>Acc</c> binary every time.
+
+ Prepending data to a binary in a loop is not efficient:
+
+ DO NOT
+ <code type="erl"><![CDATA[
+rev_list_to_binary(List) ->
+ rev_list_to_binary(List, <<>>).
+
+rev_list_to_binary([H|T], Acc) ->
+ rev_list_to_binary(T, <<H,Acc/binary>>);
+rev_list_to_binary([], Acc) ->
+ Acc.]]></code>
+
+ This is not efficient for long lists because the <c>Acc</c>
+ binary is copied every time. One way to make the function more
+ efficient is like this:
+
+ DO NOT
+ <code type="erl"><![CDATA[
+rev_list_to_binary(List) ->
+ rev_list_to_binary(lists:reverse(List), <<>>).
+
+rev_list_to_binary([H|T], Acc) ->
+ rev_list_to_binary(T, <<Acc/binary,H>>);
+rev_list_to_binary([], Acc) ->
+ Acc.]]></code>
+
+ Another way to avoid copying the binary each time is like this:
+
+ DO
+ <code type="erl"><![CDATA[
+rev_list_to_binary([H|T]) ->
+ RevTail = rev_list_to_binary(T),
+ <<RevTail/binary,H>>;
+rev_list_to_binary([]) ->
+ <<>>.]]></code>
+
+ Note that in each of the DO examples, the binary to be
+ appended to is always given as the first segment.
+
+ Binaries can be efficiently matched in the following way:
 
 DO
 <code type="erl"><![CDATA[
-- 
2.35.3

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