Re: Inline::C and arrays

[Scott Prahl]

OK,

I read perlguts.  I read perlapi.  I read Inline::C.  I read Inline::C-Cookbook.
I never did understand the Hash of Lists example.  I finally prevailed.

I offer the following up for inclusion in C-Cookbook to save someone else the
pain of doing this again --- particularly becasue there are not many examples
in the Cookbook that deal with arrays and doubles.

I am unclear if the newRV_noinc() macros at the end are correct.  I used
the newRV_noinc() because the Hash of Lists examples used them.

Suggestions for improvement would be welcome.

Thanks,
Scott
******************************************
#!/usr/bin/perl -w

my $n = 21;
my @angles = map {$_ * 3.1415926/($n-1)} (0..$n);
my ($cosine, $sine) = trig_wrap($n, \@angles);

for (0..$n-1) {
        print $_,"  ", $angles[$_],"  ", $$cosine[$_], "  ", $$sine[$_], "\n";
}

use Inline C => <<'END_OF_C_CODE';

/* this typically would be in a library */
void trig(int n, double * angles, double ** cosines, double ** sines)
{
        int i;
        *sines   = (double *) malloc(n*sizeof(double));
        *cosines = (double *) malloc(n*sizeof(double));

        for (i=0; i<n; i++) {
                (*cosines)[i] = cos(angles[i]);
                (*sines)[i] = sin(angles[i]);
        }
}

void trig_wrap(int n, SV* array_ref)
{
        Inline_Stack_Vars;
        double *cosine, *sine, *angles;
        AV *pcos, *psin, *av_ptr;
        SV** sv_ptr;
        int i;
        
/* copy values from array_ref into C array */
        angles  = (double *) malloc(n*sizeof(double));
        av_ptr = (AV*) SvRV(array_ref); 
        for (i=0; i<n; i++) {
                sv_ptr = av_fetch(av_ptr,i,0);
                angles[i] = SvNV(*sv_ptr);
        }

        trig(n, angles, &cosine, &sine);
        
/* copy values from C arrays into perl arrays */
        pcos = newAV();
        psin = newAV();
        for (i=0; i<n; i++) {
                av_push(pcos, newSVnv(cosine[i]));
                av_push(psin, newSVnv(sine[i]  ));
        }

/* get rid of C arrays */
        free(angles);
        free(sine);
        free(cosine);
        
/* return references to perl arrays */
        Inline_Stack_Reset;
        Inline_Stack_Push(newRV_noinc((SV*) pcos));
        Inline_Stack_Push(newRV_noinc((SV*) psin));
        Inline_Stack_Done;
}
END_OF_C_CODE