Re: This Fortnight on perl5-porters - 28 September-12 October 2008

[hv@crypt.org]

David Landgren <david@landgren.net> wrote:
:This Fortnight on perl5-porters - 28 September-12 October 2008
[...]
:"Perl_newSVpvf("%lld")" is broken
:
:   One other item that fell out of the Y2038+ code was that, on 32-bit
:   platforms, "printf("%lld\n", 2**32)" gives a result of -1. Michael and
:   admitted to being terrified by the code and hoped someone else could
:   dig down through it and figure out where the problem lay.
:
:     quad wrangle
:     http://xrl.us/oudxw

Apologies if this has already been addressed: I'm mostly 1-2 weeks behind
on email these days.

The problem is combo-ifdefs. First we get this:

        case 'l':
#if defined(HAS_QUAD) || defined(HAS_LONG_DOUBLE)
            if (*(q + 1) == 'l') {      /* lld, llf */
                intsize = 'q';
                q += 2; 
                break;
             }
#endif

and then we get this (for the %d case):
                default:        iv = tiv; break;
#ifdef HAS_QUAD
                case 'q':       iv = (Quad_t)tiv; break;
#endif

So when HAS_LONG_DOUBLE but not HAS_QUAD, we set intsize='q', but then
silently go to the default (%d) case at the point we consume it.

It should rather do the same as the long double case, i.e.:
                case 'q':
#ifdef HAS_QUAD
                                iv = (Quad_t)tiv; break;
#else
                                goto unknown;
#endif

.. and the same logic needs to be repeated in many #ifdef HAS_QUAD places
(and the HAS_LONG_DOUBLE places should be checked too, for completeness).
Patching just the one place fixes it for me:

zen% ./perl -Ilib -e 'printf "%lld\n", 4294967296'
%lld
zen% 

Sorry I don't have time to generate a full patch right now, I hope this
info is enough.

(It is also arguable that "%lld" isn't the most useful output, but if that
is changed thought should be given to making the analogous change for %llf.)

Hugo

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References to:

David Landgren <david@landgren.net>

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