Inline::C requires that you call PUTBACK (explicitly or via XSRETURN) because it can't do it for you because it doesn't have access to your sub's SP to "put it back".

Hm. The wrapper sub knows (or can find out) how many values were passed on the stack. For fixed-length argument lists (no ellipses), it could clean up the stack before calling the I::C sub. Indeed, it already seems to (attempt to) do that:

XS(XS_main_rnd64); /* prototype to pass -Wmissing-prototypes */
XS(XS_main_rnd64)
{
#ifdef dVAR
    dVAR; dXSARGS;
#else
    dXSARGS;
#endif
    if (items != 1)
       croak_xs_usage(cv,  "n");
    PERL_UNUSED_VAR(ax); /* -Wall */
    SP -= items;

[download]

Which is the source of my confusion regarding the need to do this (again) within the sub.

It (the wrapper sub) could also take a mark on the stack prior to invoking the I:C sub: (which it also seems to do:

    temp = PL_markstack_ptr++;

[download]
),

and then use that to determine how many (if any) values have been pushed onto the stack during the call, thereby removing the need for the I::C programmer to do this manually.

For all the world it looks like the wrapper sub were originally intended to automate this part of the process, but then something changed. Maybe the author changed his mind or couldn't get it to work. Or some other programmer went in there to correct some bug and made changes that were incompatible with the original vision. (This all pre-dates syphilis' involvement.).

The closer you start to look at this code, the more oddities and (possibly) missed opportunities you see.

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.

In reply to Re^6: XS: EXTEND/mPUSHi by BrowserUk
in thread XS: EXTEND/mPUSHi by BrowserUk

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.