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authorBjörn Gustavsson <[email protected]>2018-05-07 13:14:13 +0200
committerBjörn Gustavsson <[email protected]>2018-05-07 13:21:41 +0200
commit5e2f90735cfd78f353e549bf92bc8792ab1c6d34 (patch)
treec8f01f8e69ca59c0b79b64fd77390bea2ca83b30 /system/doc
parent4c350d64b85686b731d0888c36159b4d126e5cf1 (diff)
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Remove obsolete example in Efficiency Guide
The argument order is no longer important.
Diffstat (limited to 'system/doc')
-rw-r--r--system/doc/efficiency_guide/binaryhandling.xml82
-rw-r--r--system/doc/efficiency_guide/efficiency_guide.erl24
2 files changed, 3 insertions, 103 deletions
diff --git a/system/doc/efficiency_guide/binaryhandling.xml b/system/doc/efficiency_guide/binaryhandling.xml
index 19f40c9abe..d07ff1325f 100644
--- a/system/doc/efficiency_guide/binaryhandling.xml
+++ b/system/doc/efficiency_guide/binaryhandling.xml
@@ -357,25 +357,8 @@ all_but_zeroes_to_list(<<Byte,T/binary>>, Acc, Remaining) ->
<c>Buffer</c> from a match context to a sub binary (or do nothing if
<c>Buffer</c> is a binary already).</p>
- <p>Before you begin to think that the compiler can optimize any binary
- patterns, the following function cannot be optimized by the compiler
- (currently, at least):</p>
-
- <code type="erl"><![CDATA[
-non_opt_eq([H|T1], <<H,T2/binary>>) ->
- non_opt_eq(T1, T2);
-non_opt_eq([_|_], <<_,_/binary>>) ->
- false;
-non_opt_eq([], <<>>) ->
- true.]]></code>
-
- <p>It was mentioned earlier that the compiler can only delay creation of
- sub binaries if it knows that the binary will not be shared. In this case,
- the compiler cannot know.</p>
-
- <p>Soon it is shown how to rewrite <c>non_opt_eq/2</c> so that the delayed
- sub binary optimization can be applied, and more importantly, it is shown
- how you can find out whether your code can be optimized.</p>
+ <p>But in more complicated code, how can one know whether the
+ optimization is applied or not?</p>
<section>
<marker id="bin_opt_info"></marker>
@@ -422,67 +405,6 @@ after_zero(<<>>) ->
binary cannot be delayed, because it will be returned.
The warning for the second clause says that a sub binary will not be
created (yet).</p>
-
- <p>Let us revisit the earlier example of the code that could not
- be optimized and find out why:</p>
-
- <code type="erl"><![CDATA[
-non_opt_eq([H|T1], <<H,T2/binary>>) ->
- %% INFO: matching anything else but a plain variable to
- %% the left of binary pattern will prevent delayed
- %% sub binary optimization;
- %% SUGGEST changing argument order
- %% NOT OPTIMIZED: called function non_opt_eq/2 does not
- %% begin with a suitable binary matching instruction
- non_opt_eq(T1, T2);
-non_opt_eq([_|_], <<_,_/binary>>) ->
- false;
-non_opt_eq([], <<>>) ->
- true.]]></code>
-
- <p>The compiler emitted two warnings. The <c>INFO</c> warning refers
- to the function <c>non_opt_eq/2</c> as a callee, indicating that any
- function that call <c>non_opt_eq/2</c> cannot make delayed sub binary
- optimization. There is also a suggestion to change argument order.
- The second warning (that happens to refer to the same line) refers to
- the construction of the sub binary itself.</p>
-
- <p>Soon another example will show the difference between the
- <c>INFO</c> and <c>NOT OPTIMIZED</c> warnings somewhat clearer, but
- let us first follow the suggestion to change argument order:</p>
-
- <code type="erl"><![CDATA[
-opt_eq(<<H,T1/binary>>, [H|T2]) ->
- %% OPTIMIZED: creation of sub binary delayed
- opt_eq(T1, T2);
-opt_eq(<<_,_/binary>>, [_|_]) ->
- false;
-opt_eq(<<>>, []) ->
- true.]]></code>
-
- <p>The compiler gives a warning for the following code fragment:</p>
-
- <code type="erl"><![CDATA[
-match_body([0|_], <<H,_/binary>>) ->
- %% INFO: matching anything else but a plain variable to
- %% the left of binary pattern will prevent delayed
- %% sub binary optimization;
- %% SUGGEST changing argument order
- done;
-...]]></code>
-
- <p>The warning means that <em>if</em> there is a call to <c>match_body/2</c>
- (from another clause in <c>match_body/2</c> or another function), the
- delayed sub binary optimization will not be possible. More warnings will
- occur for any place where a sub binary is matched out at the end of and
- passed as the second argument to <c>match_body/2</c>, for example:</p>
-
- <code type="erl"><![CDATA[
-match_head(List, <<_:10,Data/binary>>) ->
- %% NOT OPTIMIZED: called function match_body/2 does not
- %% begin with a suitable binary matching instruction
- match_body(List, Data).]]></code>
-
</section>
<section>
diff --git a/system/doc/efficiency_guide/efficiency_guide.erl b/system/doc/efficiency_guide/efficiency_guide.erl
index e982bdae65..c57785aaa3 100644
--- a/system/doc/efficiency_guide/efficiency_guide.erl
+++ b/system/doc/efficiency_guide/efficiency_guide.erl
@@ -1,5 +1,5 @@
-module(efficiency_guide).
--compile(export_all).
+-compile([export_all,nowarn_export_all).
%% DO NOT
naive_reverse([H|T]) ->
@@ -71,28 +71,6 @@ all_but_zeroes_to_list(<<0,T/binary>>, Acc, Remaining) ->
all_but_zeroes_to_list(<<Byte,T/binary>>, Acc, Remaining) ->
all_but_zeroes_to_list(T, [Byte|Acc], Remaining-1).
-non_opt_eq([H|T1], <<H,T2/binary>>) ->
- non_opt_eq(T1, T2);
-non_opt_eq([_|_], <<_,_/binary>>) ->
- false;
-non_opt_eq([], <<>>) ->
- true.
-
-opt_eq(<<H,T1/binary>>, [H|T2]) ->
- opt_eq(T1, T2);
-opt_eq(<<_,_/binary>>, [_|_]) ->
- false;
-opt_eq(<<>>, []) ->
- true.
-
-match_head(List, <<_:10,Data/binary>>) ->
- match_body(List, Data).
-
-match_body([0|_], <<H,_/binary>>) ->
- done;
-match_body([H|T1], <<H,T2/binary>>) ->
- {T1,T2}.
-
count1(<<_,T/binary>>, Count) -> count1(T, Count+1);
count1(<<>>, Count) -> Count.