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    <p>Because you are sorting lexically, Try this code:</p> <pre><code>#!/usr/bin/perl use strict; use warnings; my $ref = [ 5.0e-5,4.2e-5,4.3e-5,4.4e-5,4.4e-5,4.2e-5,4.2e-5,4.0e-5]; print "Perl with cmp\n"; for my $val (sort @$ref) { printf "%f \n", $val; } print "Perl with &lt;=&gt;\n"; for my $val (sort { $a &lt;=&gt; $b } @$ref) { printf "%f \n", $val; } print "C\n"; test($ref); use Inline C =&gt; &lt;&lt;'END_OF_C_CODE'; void test(SV* sv, ...) { I32 i; I32 arrayLen; AV* data; float retval; SV** pvalue; Inline_Stack_Vars; data = SvUV(Inline_Stack_Item(0)); /* Determine the length of the array */ arrayLen = av_len(data); // sort sortsv(AvARRAY(data),av_len(data)+1,Perl_sv_cmp_locale); arrayLen = av_len(data); for (i = 0; i &lt; arrayLen+1; i++) { pvalue = av_fetch(data,i,0); /* fetch the scalar located at i .*/ retval = SvNV(*pvalue); /* dereference the scalar into a number. */ printf("%f \n",newSVnv(retval)); } } END_OF_C_CODE </code></pre> <p>Of course, lexically <code>0.00040</code> is smaller than <code>0.00042</code> as well, but you aren't comparing <code>0.00040</code> to <code>0.00042</code>; you are comparing the number <code>0.00040</code> converted to a string with the number <code>0.00042</code> converted to a string. When a number gets too large or small, Perl's stringifying logic resorts to using scientific notation. So you are sorting the set of strings </p> <pre><code>"4.2e-05", "4.2e-05", "4.2e-05", "4.3e-05", "4.4e-05", "4.4e-05", "4e-05", "5e-05" </code></pre> <p>which are properly sorted. Perl happily turns those strings back into their numbers when you ask it to with the <code>%f</code> format in <code>printf</code>. You could stringify the numbers yourself, but since you have stated you want this to be faster, that would be a mistake. You should not to be trying to optimize the program before you know where it slow (premature optimization is the root of all evil<code>*</code>). Write your code then run <a href="http://search.cpan.org/dist/Devel-NYTProf/" rel="nofollow noreferrer">Devel::NYTProf</a> against it to find where it is slow. If necessary, rewrite those portions in <a href="http://perldoc.perl.org/perlxstut.html" rel="nofollow noreferrer">XS</a> or <code>Inline::C</code> (I prefer XS). You will find that you get more speed out of choosing the right data structure than micro-optimizations like this.</p> <p><code>*</code> <a href="http://www-cs-faculty.stanford.edu/~knuth/" rel="nofollow noreferrer">Knuth, Donald</a>. <a href="http://portal.acm.org/citation.cfm?id=356640" rel="nofollow noreferrer">Structured Programming with go to Statements</a>, <a href="http://surveys.acm.org/" rel="nofollow noreferrer">ACM Journal Computing Surveys</a>, Vol 6, No. 4, Dec. 1974. p.268.</p>
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    1. POWhy does Perl's Inline::C sort 4.0e-5 after 4.4e-5?
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    1. COI would like to have the sorting in the Inline::C section for speed. This may be the problem, but how to get sortsv() to sort numerically is not well documented.
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      1. USDan Littlejohn
    2. COYou won't get any speed out of it. The sort function in Perl is written in C.
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    3. CONow, if you mean the function you are _passing_ to the sort function, that may get a speed boost, but it would have to be pretty complicated.
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