You could add an explicit conversion to IV, e.g. 

     ...
     char * str;

     sv_setiv(integer, SvIV(integer));  //  <--- here
     str = SvPV_nolen(integer);
     ...

[download]

However, when doing that, I get (note the difference in the last two digits): 

IV: 144115188075868217
IV: 144115188075868224

[download]

I suppose this is due to the insufficient precision in the NV representation...   Actually, I think it's too late to deal with this within your XS routine, as the value will already have been converted to NV when the SV gets passed to foo() - unless you use integer on the Perl side (but you already figured that out :)

In reply to Re: XS and -Duse64bitint by almut
in thread XS and -Duse64bitint by syphilis

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