2016-01-06 22:37 GMT+08:00 Marc Feeley feeley@iro.umontreal.ca:
Of course one way would be to return a double (which has 53 bits of precision) and use NaN to encode “missing tag”. I’m not kidding!
If you don’t like this approach, and I can understand why you wouldn’t, then you have to do the conversion to ___SCMOBJ by directly calling the conversion macros. Something like this:
(define uint32_tag (c-lambda (TIFF* ttag_t) scheme-object " ___U32 val; if (TIFFGetField(___arg1, ___arg2, &val) == 1) { if ((___err = ___U32_to_SCMOBJ (___PSTATE, val, &___result, ___RETURN_POS)) == ___FIX(___NO_ERR)) { ___release_scmobj (___result); } } else { ___result = ___FAL; } "))
Neat! What is the risk involved with this one - I mean, the Scheme object allocation on the Gambit heap could fail under certain circumstances. But would that only be on malloc() failure?