* Re: [PATCH] Builtin function roundeven folding implementation
[not found] ` <alpine.DEB.2.21.1908221426570.27000@digraph.polyomino.org.uk>
@ 2019-08-22 16:28 ` Tejas Joshi
2019-08-22 16:35 ` Joseph Myers
[not found] ` <CACMrGjA3UyUYcShruM-tiT=rqBiSLX9cmSVmpX0G6SfOq_r4EQ@mail.gmail.com>
1 sibling, 1 reply; 6+ messages in thread
From: Tejas Joshi @ 2019-08-22 16:28 UTC (permalink / raw)
To: gcc; +Cc: Martin Jambor, hubicka, joseph
> I'm concerned that this would produce +0.0 for an argument of -0.5 (via
> -0.5 - 0.5 - -1.0 producing +0.0) when it needs to produce -0.0.
Would the following overhaul be acceptable as the condition is
specialized for -0.5 and +0.5 only. This seems to solve the problem. I
did test the roundeven tests and it passes the tests.
void
real_roundeven (REAL_VALUE_TYPE *r, format_helper fmt,
const REAL_VALUE_TYPE *x)
{
if (is_halfway_below (x))
{
if (REAL_EXP (x) == 0)
{
*r = *x;
clear_significand_below (r, SIGNIFICAND_BITS);
}
else
{
do_add (r, x, &dconsthalf, x->sign);
if (!is_even (r))
do_add (r, r, &dconstm1, x->sign);
}
if (fmt)
real_convert (r, fmt, r);
}
else
real_round (r, fmt, x);
}
tests:
/* { dg-do link } */
extern int link_error (int);
#define TEST(FN, VALUE, RESULT) \
if (__builtin_##FN (VALUE) != RESULT) link_error (__LINE__);
int
main (void)
{
TEST(roundeven, 0, 0);
TEST(roundeven, 0.5, 0);
TEST(roundeven, -0.5, 0);
TEST(roundeven, 6, 6);
TEST(roundeven, -8, -8);
TEST(roundeven, 2.5, 2);
TEST(roundeven, 3.5, 4);
TEST(roundeven, -1.5, -2);
TEST(roundeven, 3.499, 3);
TEST(roundeven, 3.501, 4);
if (__builtin_copysign (1, __builtin_roundeven (-0.5)) != -1)
link_error (__LINE__);
return 0;
}
Thanks,
Tejas
On Thu, 22 Aug 2019 at 20:03, Joseph Myers <joseph@codesourcery.com> wrote:
>
> On Thu, 22 Aug 2019, Martin Jambor wrote:
>
> > +/* Round X to nearest integer, rounding halfway cases towards even. */
> > +
> > +void
> > +real_roundeven (REAL_VALUE_TYPE *r, format_helper fmt,
> > + const REAL_VALUE_TYPE *x)
> > +{
> > + if (is_halfway_below (x))
> > + {
> > + do_add (r, x, &dconsthalf, x->sign);
> > + if (!is_even (r))
> > + do_add (r, r, &dconstm1, x->sign);
>
> I'm concerned that this would produce +0.0 for an argument of -0.5 (via
> -0.5 - 0.5 - -1.0 producing +0.0) when it needs to produce -0.0.
>
> Note that testcases for the sign of zero results need to check e.g.
> !!__builtin_signbit on the result, or the result of calling
> __builtin_copysign* to extract the sign of the result, since 0.0 == -0.0
> so checking with ==, while necessary, is not sufficient in that case.
>
> --
> Joseph S. Myers
> joseph@codesourcery.com
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] Builtin function roundeven folding implementation
2019-08-22 16:28 ` [PATCH] Builtin function roundeven folding implementation Tejas Joshi
@ 2019-08-22 16:35 ` Joseph Myers
2019-08-22 16:56 ` Tejas Joshi
0 siblings, 1 reply; 6+ messages in thread
From: Joseph Myers @ 2019-08-22 16:35 UTC (permalink / raw)
To: Tejas Joshi; +Cc: gcc, Martin Jambor, hubicka
On Thu, 22 Aug 2019, Tejas Joshi wrote:
> > I'm concerned that this would produce +0.0 for an argument of -0.5 (via
> > -0.5 - 0.5 - -1.0 producing +0.0) when it needs to produce -0.0.
>
> Would the following overhaul be acceptable as the condition is
> specialized for -0.5 and +0.5 only. This seems to solve the problem. I
> did test the roundeven tests and it passes the tests.
I think that would be reasonable with a comment added to explain that it's
ensuring the correct sign of a zero result.
> if (__builtin_copysign (1, __builtin_roundeven (-0.5)) != -1)
> link_error (__LINE__);
I think you should have at least four tests of sign of zero result
(arguments -0.5, -0.0, 0.0 and 0.5). Probably also tests of values
between +/- 0.5 and 0, e.g. test -0.25 and 0.25 as well.
--
Joseph S. Myers
joseph@codesourcery.com
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] Builtin function roundeven folding implementation
2019-08-22 16:35 ` Joseph Myers
@ 2019-08-22 16:56 ` Tejas Joshi
2019-08-22 17:00 ` Joseph Myers
0 siblings, 1 reply; 6+ messages in thread
From: Tejas Joshi @ 2019-08-22 16:56 UTC (permalink / raw)
To: gcc; +Cc: Martin Jambor, hubicka, joseph
> I think you should have at least four tests of sign of zero result
> (arguments -0.5, -0.0, 0.0 and 0.5). Probably also tests of values
> between +/- 0.5 and 0, e.g. test -0.25 and 0.25 as well.
Okay, I have made the following changes and again, the tests pass for roundeven.
void
real_roundeven (REAL_VALUE_TYPE *r, format_helper fmt,
const REAL_VALUE_TYPE *x)
{
if (is_halfway_below (x))
{
/* Special case as -0.5 rounds to -0.0 and
similarly +0.5 rounds to +0.0. */
if (REAL_EXP (x) == 0)
{
*r = *x;
clear_significand_below (r, SIGNIFICAND_BITS);
}
else
{
do_add (r, x, &dconsthalf, x->sign);
if (!is_even (r))
do_add (r, r, &dconstm1, x->sign);
}
if (fmt)
real_convert (r, fmt, r);
}
else
real_round (r, fmt, x);
}
Tests :
/* { dg-do link } */
extern int link_error (int);
#define TEST(FN, VALUE, RESULT) \
if (__builtin_##FN (VALUE) != RESULT) link_error (__LINE__);
int
main (void)
{
TEST(roundeven, 0, 0);
TEST(roundeven, 0.5, 0);
TEST(roundeven, -0.5, 0);
TEST(roundeven, 6, 6);
TEST(roundeven, -8, -8);
TEST(roundeven, 2.5, 2);
TEST(roundeven, 3.5, 4);
TEST(roundeven, -1.5, -2);
TEST(roundeven, 3.499, 3);
TEST(roundeven, 3.501, 4);
if (__builtin_copysign (1, __builtin_roundeven (-0.5)) != -1)
link_error (__LINE__);
if (__builtin_copysign (1, __builtin_roundeven (-0.0)) != -1)
link_error (__LINE__);
if (__builtin_copysign (-1, __builtin_roundeven (0.5)) != 1)
link_error (__LINE__);
if (__builtin_copysign (-1, __builtin_roundeven (0.0)) != 1)
link_error (__LINE__);
if (__builtin_copysign (1, __builtin_roundeven (-0.25)) != -1)
link_error (__LINE__);
if (__builtin_copysign (-1, __builtin_roundeven (0.25)) != 1)
link_error (__LINE__);
return 0;
}
Thanks,
Tejas
On Thu, 22 Aug 2019 at 22:05, Joseph Myers <joseph@codesourcery.com> wrote:
>
> On Thu, 22 Aug 2019, Tejas Joshi wrote:
>
> > > I'm concerned that this would produce +0.0 for an argument of -0.5 (via
> > > -0.5 - 0.5 - -1.0 producing +0.0) when it needs to produce -0.0.
> >
> > Would the following overhaul be acceptable as the condition is
> > specialized for -0.5 and +0.5 only. This seems to solve the problem. I
> > did test the roundeven tests and it passes the tests.
>
> I think that would be reasonable with a comment added to explain that it's
> ensuring the correct sign of a zero result.
>
> > if (__builtin_copysign (1, __builtin_roundeven (-0.5)) != -1)
> > link_error (__LINE__);
>
> I think you should have at least four tests of sign of zero result
> (arguments -0.5, -0.0, 0.0 and 0.5). Probably also tests of values
> between +/- 0.5 and 0, e.g. test -0.25 and 0.25 as well.
>
> --
> Joseph S. Myers
> joseph@codesourcery.com
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] Builtin function roundeven folding implementation
2019-08-22 16:56 ` Tejas Joshi
@ 2019-08-22 17:00 ` Joseph Myers
0 siblings, 0 replies; 6+ messages in thread
From: Joseph Myers @ 2019-08-22 17:00 UTC (permalink / raw)
To: Tejas Joshi; +Cc: gcc, Martin Jambor, hubicka
On Thu, 22 Aug 2019, Tejas Joshi wrote:
> > I think you should have at least four tests of sign of zero result
> > (arguments -0.5, -0.0, 0.0 and 0.5). Probably also tests of values
> > between +/- 0.5 and 0, e.g. test -0.25 and 0.25 as well.
>
> Okay, I have made the following changes and again, the tests pass for roundeven.
Thanks, I look forward to seeing a full patch with these revisions on
gcc-patches.
--
Joseph S. Myers
joseph@codesourcery.com
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] Builtin function roundeven folding implementation
[not found] ` <alpine.DEB.2.21.1908232023080.19272@digraph.polyomino.org.uk>
@ 2019-08-25 8:25 ` Tejas Joshi
2019-08-25 9:38 ` Martin Jambor
0 siblings, 1 reply; 6+ messages in thread
From: Tejas Joshi @ 2019-08-25 8:25 UTC (permalink / raw)
To: gcc; +Cc: Martin Jambor, hubicka, joseph
I have made the respective changes and fixed the indentations and it
passes the testing.
> I encourage a followup looking for and fixing further places in the source
> tree that handle round-to-integer function families (ceil / floor / trunc
> / round / rint / nearbyint) and should handle roundeven as well, as that
> would lead to more optimization of roundeven calls. Such places aren't
> that easy to search for because most of those names are common words used
> in other contexts in the compiler. But, for example, match.pd has
> patterns
I will follow up to make these optimizations for sure.
Thanks,
Tejas
On Sat, 24 Aug 2019 at 02:08, Joseph Myers <joseph@codesourcery.com> wrote:
>
> On Fri, 23 Aug 2019, Tejas Joshi wrote:
>
> > diff --git a/gcc/builtins.c b/gcc/builtins.c
> > index 9a766e4ad63..5149d901a96 100644
> > --- a/gcc/builtins.c
> > +++ b/gcc/builtins.c
> > @@ -2056,6 +2056,7 @@ mathfn_built_in_2 (tree type, combined_fn fn)
> > CASE_MATHFN (REMQUO)
> > CASE_MATHFN_FLOATN (RINT)
> > CASE_MATHFN_FLOATN (ROUND)
> > + CASE_MATHFN (ROUNDEVEN)
>
> This should use CASE_MATHFN_FLOATN, as for the other round-to-integer
> functions.
>
> > + /* Check lowest bit, if not set, return true. */
> > + else if (REAL_EXP (r) <= SIGNIFICAND_BITS)
> > + {
> > + unsigned int n = SIGNIFICAND_BITS - REAL_EXP (r);
> > + int w = n / HOST_BITS_PER_LONG;
> > +
> > + unsigned long num = ((unsigned long)1 << (n % HOST_BITS_PER_LONG));
> > +
> > + if ((r->sig[w] & num) == 0)
> > + return true;
>
> Fix the indentation here (the braces should be indented two columns from
> the "else", the contents then two columns from the braces).
>
> > + }
> > +
> > + else
>
> And remove the stray blank line before "else".
>
> > +/* Return true if R is halfway between two integers, else return
> > + false. The function is not valid for rvc_inf and rvc_nan classes. */
> > +
> > +bool
> > +is_halfway_below (const REAL_VALUE_TYPE *r)
> > +{
> > + gcc_assert (r->cl != rvc_inf);
> > + gcc_assert (r->cl != rvc_nan);
> > + int i;
>
> Explicitly check for rvc_zero and return false in that case (that seems to
> be the convention in real.c, rather than relying on code using REAL_EXP to
> do something sensible for zero, which has REAL_EXP of 0).
>
> > + else if (REAL_EXP (r) < SIGNIFICAND_BITS)
> > + {
>
> Another place to fix indentation.
>
> > +void
> > +real_roundeven (REAL_VALUE_TYPE *r, format_helper fmt,
> > + const REAL_VALUE_TYPE *x)
> > +{
> > + if (is_halfway_below (x))
> > + {
>
> Again, fix indentation throughout this function.
>
> The patch is OK with those fixes, assuming the fixed patch passes testing.
> I encourage a followup looking for and fixing further places in the source
> tree that handle round-to-integer function families (ceil / floor / trunc
> / round / rint / nearbyint) and should handle roundeven as well, as that
> would lead to more optimization of roundeven calls. Such places aren't
> that easy to search for because most of those names are common words used
> in other contexts in the compiler. But, for example, match.pd has
> patterns
>
> /* trunc(trunc(x)) -> trunc(x), etc. */
>
> /* f(x) -> x if x is integer valued and f does nothing for such values. */
>
> /* truncl(extend(x)) -> extend(trunc(x)), etc., if x is a double. */
>
> /* truncl(extend(x)) and trunc(extend(x)) -> extend(truncf(x)), etc.,
> if x is a float. */
>
> which should apply to roundeven as well.
>
> --
> Joseph S. Myers
> joseph@codesourcery.com
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] Builtin function roundeven folding implementation
2019-08-25 8:25 ` Tejas Joshi
@ 2019-08-25 9:38 ` Martin Jambor
0 siblings, 0 replies; 6+ messages in thread
From: Martin Jambor @ 2019-08-25 9:38 UTC (permalink / raw)
To: Tejas Joshi, gcc; +Cc: hubicka, joseph
Hi,
On Sun, Aug 25 2019, Tejas Joshi wrote:
> I have made the respective changes and fixed the indentations and it
> passes the testing.
Great, please send the patch (to me and to the mailing list too), so
that I can commit it.
Thanks,
Martin
^ permalink raw reply [flat|nested] 6+ messages in thread
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2019-08-22 16:28 ` [PATCH] Builtin function roundeven folding implementation Tejas Joshi
2019-08-22 16:35 ` Joseph Myers
2019-08-22 16:56 ` Tejas Joshi
2019-08-22 17:00 ` Joseph Myers
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2019-08-25 8:25 ` Tejas Joshi
2019-08-25 9:38 ` Martin Jambor
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