[EMAIL PROTECTED] writes:
> I want a reduced test case for this problem for bugzilla, but don't
> really know the exact cause. I _think_ code is being improperly
> optimized away, but I don't know. This function is part of a
> BigInteger library, and works perfectly upto and including -O2, but
> produces bogus results at -O3, unless I uncomment the debug_msg()
> line, which just dumps the contents of 'i' to the screen. I'm
> guessing that without it, the compiler fails to notice that i's
> contents are being accessed via the _front8/_back8 pointers, and
> throws the preceeding 'i' related code away. Heres the code:
>
> void Integer::export_bytes(Data& _buffer, PortMode _mode) const
> {
> debug_scope("export_bytes(Data&)");
>
> Integer i(*this,1);
>
> if (_mode==SIGNED) {
> if (*mBack & TOP_BIT)
> i.grow(1,0);
> if (sign()<0)
> i.twoscomplement();
> }
>
> for (UnsignedW* p=i.mFront; p<=i.mBack; p++)
> *p = host2little(*p);
>
> Unsigned8* _front8 = reinterpret_cast<Unsigned8*>(i.mFront);
> Unsigned8* _back8 = _front8+(i.mSize*WORD_BYTES)-1;
> if (_mode==UNSIGNED)
> while (_back8!=_front8 and *_back8==0)
> _back8--;
> else if (mSign==1)
> while (_back8!=_front8 and *_back8==0 and
> !(*(_back8-1)&0x80))
> _back8--;
> else
> while (_back8!=_front8 and *_back8==0xff and
> *(_back8-1)&0x80)
> _back8--;
>
> //debug_msg(String("Force i\n")+i.dump());
>
> _buffer.assign(_front8, _back8+1);
> }
>
> Any thoughts on how to proceed?
I think your code is broken. A reinterpret_cast from foo* to bar* is
only well-defined if foo and bar are compatible types or one of
{foo,bar} is type char. I can't be sure from your code, but I'm
guessing that i.mFront is not declared as a pointer to Unsigned8, but
as a pointer to an incompatible type UnsignedW.
Andrew.
