Why is Perl Inline :: C sort 4.0e-5 after 4.4e-5?

Question

I built the Perl Inline :: C module , but there is some weirdness in sorting. Does anyone know why this would look like this? Why is 4.0e-5 not the first?

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]; 

use Inline C => <<'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),arrayLen+1,Perl_sv_cmp_locale);

  for (i = 0; i < 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

test ($ ref);

0.000042
0.000042
0.000042
0.000043
0.000044
0.000044
0.000040
0.000050

Answer 1

Answer with the help of people using http://www.perlmonks.org/?node_id=761015

(DProf), 4-
= 0,543205
+ = 0,585454

% ExclSec CumulS #Calls sec/call Csec/c
 100. 0,590 0,490 100000 0,0000 0,0000 test_inline_c_pkg:: percent2

= 2,151647
+ = 1.991647

% ExclSec CumulS #Calls sec/call Csec/c
 104. 2.080 1.930 100000 0.0000 0.0000 main:: percent2

use Inline C => <<'END_OF_C_CODE';

#define SvSIOK(sv) ((SvFLAGS(sv) & (SVf_IOK|SVf_IVisUV)) == SVf_IOK)
#define SvNSIV(sv) (SvNOK(sv) ? SvNVX(sv) : (SvSIOK(sv) ? SvIVX(sv) : sv_2nv(sv)))

static I32 S_sv_ncmp(pTHX_ SV *a, SV *b) {

  const NV nv1 = SvNSIV(a);
  const NV nv2 = SvNSIV(b);
  return nv1 < nv2 ? -1 : nv1 > nv2 ? 1 : 0;
}

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 descending (send numerical sort function S_sv_ncmp) */
  sortsv(AvARRAY(data),arrayLen+1, S_sv_ncmp);

  for (i = 0; i < 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

Answer 2

, :

#!/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 <=>\n";
for my $val (sort { $a <=> $b } @$ref) {
    printf "%f \n", $val;
}

print "C\n";

test($ref);

use Inline C => <<'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 < 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

, 0.00040 , 0.00042, 0.00040 0.00042; 0.00040, 0.00042, . , Perl, , . ,

"4.2e-05", "4.2e-05", "4.2e-05", "4.3e-05", "4.4e-05", "4.4e-05", "4e-05", "5e-05"

. Perl , %f printf. , , , , . , , ( - *). Devel:: NYTProf, , . , XS Inline::C ( XS). , , -, .

* , . , ACM Journal Computing Surveys, 6, № 4, 1974. .268.

Answer 3

Perl_sv_cmp_locale- This is your sort function, which I suspect is a lexical comparison. Find a numerical sort or write yourself.