Re: rpcrt4: Introduce a new function, safe_multiply, which will raise an exception if a multiply overflows a 4-byte integer.

[Alexandre Julliard]

Robert Shearman  writes:
> - unsigned char overflow;
>
> +#if defined(__i386__) && defined (__GNUC__)
> - __asm__(
> -
>        "mull %3\n\t"
> -
>        "seto %%cl"
> -
>        : "=a" (ret), "=c" (overflow) /* outputs: eax, cl */
> -
>        : "%a" (a), "rm" (b) /* inputs: eax, any register or memory
> -
>                              * address (params are interchangable) */
> -
>        : "edx" /* edx clobbered */);
>
> +#else
> - ret = a * b;
> - overflow = (b && (ret / b != a));
>
> +#endif

That asm seems really overkill. Something like:

ULONGLONG ret = (ULONGLONG)a * b;
  if (ret > 0xffffffff)

will generate pretty much the same code with a recent gcc, and it's a
lot more readable.

BTW could you please add a sequence number in the subject line for
your patches?  It makes things a lot easier for me when the mails
arrive out of order. Thanks.

rpcrt4: Introduce a new function, safe_multiply, which will raise an exception if a multiply overflows a 4-byte integer.

[Robert Shearman]

Alexandre Julliard wrote:
> Robert Shearman  writes:
> > - unsigned char overflow;
> >
> > +#if defined(__i386__) && defined (__GNUC__)
> > - __asm__(
> > -
> >        "mull %3\n\t"
> > -
> >        "seto %%cl"
> > -
> >        : "=a" (ret), "=c" (overflow) /* outputs: eax, cl */
> > -
> >        : "%a" (a), "rm" (b) /* inputs: eax, any register or memory
> > -
> >                              * address (params are interchangable) */
> > -
> >        : "edx" /* edx clobbered */);
> >
> > +#else
> > - ret = a * b;
> > - overflow = (b && (ret / b != a));
> >
> > +#endif
>
> That asm seems really overkill. Something like:
>
> ULONGLONG ret = (ULONGLONG)a * b;
>  if (ret > 0xffffffff)
>
> will generate pretty much the same code with a recent gcc, and it's a
> lot more readable.

Indeed it does. I'll resubmit the patch set with this change.