On Tue, 5 Jul 2016, Jan Hubicka wrote: > > On Tue, 5 Jul 2016, Richard Biener wrote: > > > > >given widest_int has only precision of TImode on x86_64? > > > > Is that the case? The comments say: > > > > It is really finite precision math where the precision is 4 times the > > size of the largest integer that the target port can represent. > > > > And the target has > > > > /* Keep the OI and XI modes from confusing the compiler into thinking > > that these modes could actually be used for computation. They are > > only holders for vectors during data movement. */ > > #define MAX_BITSIZE_MODE_ANY_INT (128) > > > > I would thus expect widest_int to have at 512 bits on x86_64 > > (possibly more depending on the exact definition of largest > > integer). > > I think that comment is just confusing. (I got trapped by it, too) > > /* The MAX_BITSIZE_MODE_ANY_INT is automatically generated by a very > early examination of the target's mode file. The WIDE_INT_MAX_ELTS > can accomodate at least 1 more bit so that unsigned numbers of that > mode can be represented as a signed value. Note that it is still > possible to create fixed_wide_ints that have precisions greater than > MAX_BITSIZE_MODE_ANY_INT. This can be useful when representing a > double-width multiplication result, for example. */ > > #define WIDE_INT_MAX_ELTS \ > ((MAX_BITSIZE_MODE_ANY_INT + HOST_BITS_PER_WIDE_INT) / > HOST_BITS_PER_WIDE_INT) > > #define WIDE_INT_MAX_PRECISION (WIDE_INT_MAX_ELTS * HOST_BITS_PER_WIDE_INT) > > typedef FIXED_WIDE_INT (WIDE_INT_MAX_PRECISION) widest_int; > > My reading is that the type will end up being 128+64 bits, but there is only > one extra bit guarnatee in general, which is taken by sign.
Yeah, I think the other comment should be adjusted accordingly. I didn't remember we have that one extra bit either ... ;) (given wide-ints have unsigned variants of ops I wonder if it is really necessary, but who knows - the wide-int rep w/o a sign is really sth odd and I blame RTL for it). Richard. > Honza > > > > -- > > Marc Glisse > > -- Richard Biener <rguent...@suse.de> SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nuernberg)
