Re: Setting precision for a PSImode type

[Georg-Johann Lay <avr at gjlay dot de>]

Bernd Schmidt wrote:
> On 03/05/2012 05:24 PM, Peter Bigot wrote:
>> And is there any reason (other than it doesn't seem to have been done
>> before) to believe PSImode is the wrong way to support a
>> general-purpose 20-bit integral type in gcc?
> 
> If you're using 4.7.0, it should be possible to use FRACTIONAL_INT_MODE
> and get reasonable results. However, it hasn't been tested much, since
> the final bits of the patch series which would have added 40 bit int
> support to the C frontend didn't make it in. See the discussion following
>   http://gcc.gnu.org/ml/gcc-patches/2011-07/msg00079.html

The avr backend defines a 24-bit scalar integer type by

FRACTIONAL_INT_MODE (PSI, 24, 3);

INT_MODE (PSI, 3) shred the compiler at some place, don't remember where.

The avr 24-bit types don't work smooth, see PR51527.

Johann