in reply to Re^2: perl inline::c sorting problem
in thread perl inline::c sorting problem

PP_sort.c contains all these routines which appear to be defined such that they could be used as alternatives to Perl_sv_cmp: 

S_sortcv(pTHX_ SV *a, SV *b)
S_sortcv_stacked(pTHX_ SV *a, SV *b)
S_sortcv_xsub(pTHX_ SV *a, SV *b)

S_sv_ncmp(pTHX_ SV *a, SV *b)
S_sv_i_ncmp(pTHX_ SV *a, SV *b)

S_amagic_ncmp(pTHX_ register SV *a, register SV *b)
S_amagic_i_ncmp(pTHX_ register SV *a, register SV *b)
S_amagic_cmp(pTHX_ register SV *str1, register SV *str2)
S_amagic_cmp_locale(pTHX_ register SV *str1, register SV *str2)

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They are prototyped in proto.h and aliased in embed.h, but even including those explicitly does not allow them to be seen at compile time?

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.
"Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."

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Re^4: perl inline::c sorting problem
by dalittle (Novice) on Apr 30, 2009 at 18:44 UTC
    The perl api is not very clear here. I have been trying to write my own numberical sort function (for Perl_sv_cmp) and am not sure if I even have the right args. It seems simple enough, but I have not been able to figure it out. 
    sortsv(AvARRAY(data), arrayLen+1, Perl_sv_cmp);
to
sortsv(AvARRAY(data), arrayLen+1, numerical_cmp);

???
I32 numerical_cmp(SV* sv1,SV* sv2) {

  double num1;
  double num2;

  num1 = (double)*sv1;
  num2 = (double)*sv2;

  if (num1 == num2) {
    return 0;
  }
  else if (num1 > num2) {
    return 1;
  }
  else {
    return -1;
  }
}

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[reply]
[d/l]

      I'd just steal the implementation from PP_sort.c. You have to also grab a couple of #defines: 

      use warnings;
use Inline C => Config =>
    NAME => 'IC_sort',
    CLEAN_AFTER_BUILD => 0,
    BUILD_NOISY => 1;

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(AV* data) {

    I32 i;
    I32 arrayLen;
    SV** pvalue;

    if( SvTYPE( data ) != SVt_PVAV )
        croak( "Requires an array ref ( type %d)\n",
            SvTYPE( data )
        );

    arrayLen = av_len(data);

    sortsv(AvARRAY(data),arrayLen+1, S_sv_ncmp);

    for (i = 0; i < arrayLen+1; i++) {

        pvalue = av_fetch(data,i,0);
        printf("%s \n", SvPV_nolen( *pvalue ) );
    }
}

END_OF_C_CODE

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];

test($ref);

      [download]

      That works! However, there is something I do not understand about: 

      #define SvNSIV(sv) ( SvNOK(sv) ? SvNVX(sv) : ( SvSIOK(sv) ? SvIVX(sv) 
+: sv_2nv(sv) ) )
...
    const NV nv1 = SvNSIV(a);

      [download]

      If the value is an NV, it grabs it. But if it is an IV, it grabs the IV and assigns it to the NV without coercion. Seems to work okay for mixed ints and floats and I don't see any warnings, so I guess that's yet another mystery to put down to "the magic of XS".

      Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
      "Science is about questioning the status quo. Questioning authority".
      In the absence of evidence, opinion is indistinguishable from prejudice.
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[d/l]
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        Wow, this is exactly what I needed. Really speeds up my code, thanks so much !!!!!!!!!!!!

        As for the float/int question, I believe an int is the lower bits of a float so as long as the variable is declared a float it should not matter.

        Now off to try out my new toy on my heap of data. :)
[reply]
        "the magic of XS"

        No, just the magic of the C standard. Very much like how double n = 1; doesn't generate a warning. Some compilers might give you a warning if assigning a long long value into a non-long double, at least if the long long value is "big" enough, but that is beyond my level of knowledge of such things at this point. The typical case of a 4-byte IV and an 8-byte NV means there is never even a single bit lost by such an assignment and I clearly recall that the C standard specifies that such is allowed without complaint.

        - tye        

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