I'll ask it in the simplest most lame terms I can, since I am missing something very fundamental in perl

I have a C function: 
double do_nothing(double x[], int sizeOfX)

[download]
this is what it does: 
double do_nothing(double x[], int sizeOfX)
{
  int index;
  for(index=0; index<sizeOfX; index++)
  {
    x[index]=1;
  }
  return x[0];
}

[download]

what should be my XS function??? How do I write it so the XS function takes array and a number, pass it to the C function, return the array so I can read its cell through perl?

I know it should start with this: 

double
do_nothing(x, sizeOFX)
  AV * x
  int sizeOfX

[download]

Please, long answers - I'm dumb. I couldn't find a single example on the internet which explains it and no reference to perlXS or perlguts documentation (I'm already reading them - all 34 pages of perlXS and 45 pages of perlguts, but I learn better from examples)

In reply to perl XS - passing array to C and getting it back by kopolov

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.