Re: [PATCH 3/4 v3][PR 67328] Added bool conversion for wide_ints

[Yuri Gribov <tetra2005@gmail.com>]

On Tue, May 30, 2017 at 11:35 AM, Richard Sandiford
<richard.sandiford@linaro.org> wrote:
> Yuri Gribov <tetra2005@gmail.com> writes:
>> On Tue, May 30, 2017 at 7:35 AM, Richard Sandiford
>> <richard.sandiford@linaro.org> wrote:
>>> Yuri Gribov <tetra2005@gmail.com> writes:
>>>> From 330209f721a598ec393dcb5d62de3457ee282153 Mon Sep 17 00:00:00 2001
>>>> From: Yury Gribov <tetra2005@gmail.com>
>>>> Date: Fri, 26 May 2017 07:53:10 +0100
>>>> Subject: [PATCH 3/4] Added bool conversion for wide_ints.
>>>>
>>>> gcc/
>>>> 2017-05-26  Yury Gribov  <tetra2005@gmail.com>
>>>>
>>>>       * wide-int.cc (wi::zero_p_large): New method.
>>>>       * wide-int.h (wi::zero_p): New method.
>>>
>>> Do you still need this bit?  It looks like it isn't used by the other
>>> parts of the series.
>>>
>>> The idea was that wi::eq_p (x, 0) (or just x == 0, if x is a
>>> wide-int-based type) is supposed to be as fast as a dedicated zero check.
>>> It'd be OK to have a helper function anyway, but it should probably be
>>> defined using wi::eq_p.
>>>
>>> The zero_p_large fallback can never return true, since a zero of
>>> any precision will have a length of 1.
>>
>> Thanks Richard, I'll update the patch. The bool check is used in
>> successive patch (4/4), in
>>      widest_int mask = wi::to_widest (@2);
>>      bool mask_all_ones_p = !(mask & (mask + 1));
>
> Ah, OK.  That's equivalent to mask == -1 (or wi::eq_p (@2, -1), to avoid
> the temporary).

Hm, is it? Current check ensures that N consecutive LSBs are set, not
that all bits are set. Perhaps variable name should be changed to
reflect this better.

> I think it'd be better to use one of those instead.
> There's an argument that if ! is defined, it should return an integer
> of the same precision as the argument.

True. Perhaps I should make separate
  wide_int operator !()
and
  bool operator bool()

-I