Re: About GSOC.

[Tejas Joshi <tejasjoshi9673@gmail.com>]

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Hello.
The f128 suffix worked. Based on all the corrections you all pointed
out, I have created another patch. I think I took most of the things
under consideration but please mention if I missed anything. The
following test cases were inspected with this patch. I am not sure if
the second test case is supposed to be carried out like I did.

Thanks,
-Tejas

/* { 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);

  return 0;
}

second test case :

/* { dg-do link } */
/* { dg-add-options float128 } */
/* { dg-require-effective-target float128 } */

extern int link_error (int);

#define TEST(FN, VALUE, RESULT) \
  if (__builtin_##FN (VALUE) != RESULT) link_error (__LINE__);

int
main (void)
{
  TEST(roundevenf128,  (0x1p64+0.5), (0x1p64));

  return 0;
}

On Fri, 31 May 2019 at 15:41, Martin Jambor <mjambor@suse.cz> wrote:
>
> On Thu, May 30 2019, Segher Boessenkool wrote:
> > On Thu, May 30, 2019 at 07:08:45PM +0200, Martin Jambor wrote:
> >> Interesting, I was also puzzled for a moment.  But notice that:
> >>
> >> int main ()
> >> {
> >>     _Float128 x = 18446744073709551617.5f128;
> >>     _Float128 y = __builtin_roundf128 (x);
> >> }
> >>
> >> behaves as expected... the difference is of course the suffix pegged to
> >> the literal constant (see
> >> https://gcc.gnu.org/onlinedocs/gcc-9.1.0/gcc/Floating-Types.html).
> >>
> >> I would also expect GCC to use a larger type if a constant does not fit
> >> into a double, but apparently that does not happen.  I would have to
> >> check but it is probably the right behavior according to the standard.
> >
> > 6.4.4.2/4: "An unsuffixed floating constant has type double."  I don't
> > think your suggestion would be okay?
>
> Sorry if I was not clear but I was definitely not suggesting that we
> change this (or anything).  I wrote that I was also surprised but
> believed that GCC was doing the correct thing.
>
> Thanks for pointing out where exactly the standard says what has to be
> done though.
>
> Martin

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diff --git a/gcc/builtins.c b/gcc/builtins.c
index 25e01e4092b..0b2d6bf82f9 100644
--- a/gcc/builtins.c
+++ b/gcc/builtins.c
@@ -2067,6 +2067,7 @@ mathfn_built_in_2 (tree type, combined_fn fn)
     CASE_MATHFN (REMQUO)
     CASE_MATHFN_FLOATN (RINT)
     CASE_MATHFN_FLOATN (ROUND)
+    CASE_MATHFN (ROUNDEVEN)
     CASE_MATHFN (SCALB)
     CASE_MATHFN (SCALBLN)
     CASE_MATHFN (SCALBN)
diff --git a/gcc/builtins.def b/gcc/builtins.def
index ef89729fd0c..f284a3eae3b 100644
--- a/gcc/builtins.def
+++ b/gcc/builtins.def
@@ -542,12 +542,18 @@ DEF_C99_BUILTIN        (BUILT_IN_RINTL, "rintl", BT_FN_LONGDOUBLE_LONGDOUBLE, AT
 #define RINT_TYPE(F) BT_FN_##F##_##F
 DEF_EXT_LIB_FLOATN_NX_BUILTINS (BUILT_IN_RINT, "rint", RINT_TYPE, ATTR_CONST_NOTHROW_LEAF_LIST)
 #undef RINT_TYPE
+DEF_EXT_LIB_BUILTIN    (BUILT_IN_ROUNDEVEN, "roundeven", BT_FN_DOUBLE_DOUBLE, ATTR_CONST_NOTHROW_LEAF_LIST)
+DEF_EXT_LIB_BUILTIN    (BUILT_IN_ROUNDEVENF, "roundevenf", BT_FN_FLOAT_FLOAT, ATTR_CONST_NOTHROW_LEAF_LIST)
+DEF_EXT_LIB_BUILTIN    (BUILT_IN_ROUNDEVENL, "roundevenl", BT_FN_LONGDOUBLE_LONGDOUBLE, ATTR_CONST_NOTHROW_LEAF_LIST)
 DEF_C99_BUILTIN        (BUILT_IN_ROUND, "round", BT_FN_DOUBLE_DOUBLE, ATTR_CONST_NOTHROW_LEAF_LIST)
 DEF_C99_BUILTIN        (BUILT_IN_ROUNDF, "roundf", BT_FN_FLOAT_FLOAT, ATTR_CONST_NOTHROW_LEAF_LIST)
 DEF_C99_BUILTIN        (BUILT_IN_ROUNDL, "roundl", BT_FN_LONGDOUBLE_LONGDOUBLE, ATTR_CONST_NOTHROW_LEAF_LIST)
 #define ROUND_TYPE(F) BT_FN_##F##_##F
 DEF_EXT_LIB_FLOATN_NX_BUILTINS (BUILT_IN_ROUND, "round", ROUND_TYPE, ATTR_CONST_NOTHROW_LEAF_LIST)
 #undef ROUND_TYPE
+#define ROUNDEVEN_TYPE(F) BT_FN_##F##_##F
+DEF_EXT_LIB_FLOATN_NX_BUILTINS (BUILT_IN_ROUNDEVEN, "roundeven", ROUNDEVEN_TYPE, ATTR_CONST_NOTHROW_LEAF_LIST)
+#undef ROUNDEVEN_TYPE
 DEF_EXT_LIB_BUILTIN    (BUILT_IN_SCALB, "scalb", BT_FN_DOUBLE_DOUBLE_DOUBLE, ATTR_MATHFN_FPROUNDING_ERRNO)
 DEF_EXT_LIB_BUILTIN    (BUILT_IN_SCALBF, "scalbf", BT_FN_FLOAT_FLOAT_FLOAT, ATTR_MATHFN_FPROUNDING_ERRNO)
 DEF_EXT_LIB_BUILTIN    (BUILT_IN_SCALBL, "scalbl", BT_FN_LONGDOUBLE_LONGDOUBLE_LONGDOUBLE, ATTR_MATHFN_FPROUNDING_ERRNO)
diff --git a/gcc/fold-const-call.c b/gcc/fold-const-call.c
index 06a420601c0..54315d057a2 100644
--- a/gcc/fold-const-call.c
+++ b/gcc/fold-const-call.c
@@ -792,6 +792,15 @@ fold_const_call_ss (real_value *result, combined_fn fn,
 	}
       return false;
 
+    CASE_CFN_ROUNDEVEN:
+    CASE_CFN_ROUNDEVEN_FN:
+      if (!REAL_VALUE_ISNAN (*arg) || !flag_errno_math)
+  {
+    real_roundeven (result, format, arg);
+    return true;
+  }
+      return false;
+
     CASE_CFN_LOGB:
       return fold_const_logb (result, arg, format);
 
@@ -854,6 +863,10 @@ fold_const_call_ss (wide_int *result, combined_fn fn,
       return fold_const_conversion (result, real_round, arg,
 				    precision, format);
 
+    CASE_CFN_ROUNDEVEN:
+    CASE_CFN_ROUNDEVEN_FN:
+      return fold_const_conversion (result, real_roundeven, arg, precision, format);
+
     CASE_CFN_IRINT:
     CASE_CFN_LRINT:
     CASE_CFN_LLRINT:
diff --git a/gcc/fold-const.c b/gcc/fold-const.c
index 59cedeafd71..ab96f197d5f 100644
--- a/gcc/fold-const.c
+++ b/gcc/fold-const.c
@@ -329,6 +329,8 @@ negate_mathfn_p (combined_fn fn)
     CASE_CFN_LLROUND:
     CASE_CFN_LROUND:
     CASE_CFN_ROUND:
+    CASE_CFN_ROUNDEVEN:
+    CASE_CFN_ROUNDEVEN_FN:
     CASE_CFN_SIN:
     CASE_CFN_SINH:
     CASE_CFN_TAN:
@@ -13060,6 +13062,8 @@ tree_call_nonnegative_warnv_p (tree type, combined_fn fn, tree arg0, tree arg1,
     CASE_CFN_RINT_FN:
     CASE_CFN_ROUND:
     CASE_CFN_ROUND_FN:
+    CASE_CFN_ROUNDEVEN:
+    CASE_CFN_ROUNDEVEN_FN:
     CASE_CFN_SCALB:
     CASE_CFN_SCALBLN:
     CASE_CFN_SCALBN:
@@ -13583,6 +13587,8 @@ integer_valued_real_call_p (combined_fn fn, tree arg0, tree arg1, int depth)
     CASE_CFN_RINT_FN:
     CASE_CFN_ROUND:
     CASE_CFN_ROUND_FN:
+    CASE_CFN_ROUNDEVEN:
+    CASE_CFN_ROUNDEVEN_FN:
     CASE_CFN_TRUNC:
     CASE_CFN_TRUNC_FN:
       return true;
diff --git a/gcc/real.c b/gcc/real.c
index f822ae82d61..541fa6b6e43 100644
--- a/gcc/real.c
+++ b/gcc/real.c
@@ -5010,6 +5010,80 @@ real_round (REAL_VALUE_TYPE *r, format_helper fmt,
     real_convert (r, fmt, r);
 }
 
+/* Return true if integer part of R is even, else return false. */
+
+bool
+is_even (REAL_VALUE_TYPE *r)
+{
+  if (REAL_EXP (r) <= 0)
+    return false;
+
+  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;
+  }
+  return false;
+}
+
+/* Return true if R is halfway between two integers, else return false. */
+
+bool
+is_halfway_below (const REAL_VALUE_TYPE *r)
+{
+  if (REAL_EXP (r) < 0)
+    return false;
+
+  if (REAL_EXP (r) == 0)
+  {
+    unsigned long temp = ((unsigned long)1 << 63);
+
+    if (((r->sig[SIGSZ-1] & temp) != 0) && ((r->sig[SIGSZ-1] & (temp-1)) == 0))
+      return true;
+    else
+      return false;
+  }
+
+  else if (REAL_EXP (r) < SIGNIFICAND_BITS)
+  {
+    unsigned int n = SIGNIFICAND_BITS - REAL_EXP (r);
+    int i, w = n / HOST_BITS_PER_LONG;
+
+    for (i = 0; i < w; ++i)
+    {
+      if (r->sig[i] != 0)
+        return false;
+    }
+
+    unsigned long num = ((unsigned long)1 << ((n - 1) % HOST_BITS_PER_LONG));
+
+    if (((r->sig[w] & num) != 0) && ((r->sig[w] & (num-1)) == 0))
+      return true;
+  }
+  return false;
+}
+
+/* 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);
+  }
+  else
+    real_round (r, fmt, x);
+}
+
 /* Set the sign of R to the sign of X.  */
 
 void
diff --git a/gcc/real.h b/gcc/real.h
index 0ce42565708..ebe66d234af 100644
--- a/gcc/real.h
+++ b/gcc/real.h
@@ -41,11 +41,18 @@ struct GTY(()) real_value {
      sure they're packed together, otherwise REAL_VALUE_TYPE_SIZE will
      be miscomputed.  */
   unsigned int /* ENUM_BITFIELD (real_value_class) */ cl : 2;
+  /* 1 if number is decimal floating point */
   unsigned int decimal : 1;
+  /* 1 if number is negative */
   unsigned int sign : 1;
+  /* 1 if number is signalling */
   unsigned int signalling : 1;
+  /* 1 if number is canonical
+  All are generally used for handling cases in real.c */
   unsigned int canonical : 1;
+  /* unbiased exponent of the number */
   unsigned int uexp : EXP_BITS;
+  /* significand of the number */
   unsigned long sig[SIGSZ];
 };
 
@@ -499,6 +506,8 @@ extern void real_ceil (REAL_VALUE_TYPE *, format_helper,
 		       const REAL_VALUE_TYPE *);
 extern void real_round (REAL_VALUE_TYPE *, format_helper,
 			const REAL_VALUE_TYPE *);
+extern void real_roundeven (REAL_VALUE_TYPE *, format_helper,
+      const REAL_VALUE_TYPE *);
 
 /* Set the sign of R to the sign of X.  */
 extern void real_copysign (REAL_VALUE_TYPE *, const REAL_VALUE_TYPE *);