Re: gawk compl()

[Andrew J. Schorr]

Hi Karel,

On Mon, Oct 10, 2005 at 02:19:49PM +0200, Karel Zak wrote:
> $ gawk 'BEGIN {printf("%#x\n", compl(0xFFFF0000)) }'
> 0x1fffff0000ffff
> 
> I see same output for 3.1.5, 3.1.4 and 3.1.3. It seems that version
> 3.1.2 returns correct output (it means 0xffff).

Actually, the code seems to be working correctly.  Your code
relies on the assumption that the internal operation is working
on a 32-bit integer.  But in fact, the code in builtin.c:do_compl()
is using a uintmax_t type for the calculations.  And on my 32-bit x86
system, it is defined as follows:

   typedef unsigned long long int uintmax_t;

So, in fact, the calculation is being done with 64 bits.
Therefore ~0xFFFF0000 = 0xFFFFFFFF0000FFFF.  This is
then converted to floating point and gets truncated
in the process.

At the moment, all of the bitwise operators seem to be
implemented using uintmax_t.  This is not really problematic
for the other operators, but it is certainly confusing
for compl()...

Regard,
Andy