1 files changed, 229 insertions, 14 deletions

diff --git a/sysdeps/ieee754/ldbl-128ibm/s_fmal.c b/sysdeps/ieee754/ldbl-128ibm/s_fmal.c
index eb3ee3cfb8..e72a3e4d59 100644
--- a/sysdeps/ieee754/ldbl-128ibm/s_fmal.c
+++ b/sysdeps/ieee754/ldbl-128ibm/s_fmal.c
@@ -1,5 +1,5 @@
 /* Compute x * y + z as ternary operation.
-   Copyright (C) 2011-2016 Free Software Foundation, Inc.
+   Copyright (C) 2011-2018 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
    Contributed by David Flaherty <flaherty@linux.vnet.ibm.com>.
 
@@ -17,25 +17,240 @@
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */
 
+#include <fenv.h>
+#include <float.h>
 #include <math.h>
+#include <math-barriers.h>
+#include <math_private.h>
+#include <math-underflow.h>
 #include <math_ldbl_opt.h>
+#include <mul_split.h>
+#include <stdlib.h>
+
+/* Calculate X + Y exactly and store the result in *HI + *LO.  It is
+   given that |X| >= |Y| and the values are small enough that no
+   overflow occurs.  */
+
+static void
+add_split (double *hi, double *lo, double x, double y)
+{
+  /* Apply Dekker's algorithm.  */
+  *hi = x + y;
+  *lo = (x - *hi) + y;
+}
+
+/* Value with extended range, used in intermediate computations.  */
+typedef struct
+{
+  /* Value in [0.5, 1), as from frexp, or 0.  */
+  double val;
+  /* Exponent of power of 2 it is multiplied by, or 0 for zero.  */
+  int exp;
+} ext_val;
+
+/* Store D as an ext_val value.  */
+
+static void
+store_ext_val (ext_val *v, double d)
+{
+  v->val = __frexp (d, &v->exp);
+}
+
+/* Store X * Y as ext_val values *V0 and *V1.  */
+
+static void
+mul_ext_val (ext_val *v0, ext_val *v1, double x, double y)
+{
+  int xexp, yexp;
+  x = __frexp (x, &xexp);
+  y = __frexp (y, &yexp);
+  double hi, lo;
+  mul_split (&hi, &lo, x, y);
+  store_ext_val (v0, hi);
+  if (hi != 0)
+    v0->exp += xexp + yexp;
+  store_ext_val (v1, lo);
+  if (lo != 0)
+    v1->exp += xexp + yexp;
+}
+
+/* Compare absolute values of ext_val values pointed to by P and Q for
+   qsort.  */
+
+static int
+compare (const void *p, const void *q)
+{
+  const ext_val *pe = p;
+  const ext_val *qe = q;
+  if (pe->val == 0)
+    return qe->val == 0 ? 0 : -1;
+  else if (qe->val == 0)
+    return 1;
+  else if (pe->exp < qe->exp)
+    return -1;
+  else if (pe->exp > qe->exp)
+    return 1;
+  else
+    {
+      double pd = fabs (pe->val);
+      double qd = fabs (qe->val);
+      if (pd < qd)
+	return -1;
+      else if (pd == qd)
+	return 0;
+      else
+	return 1;
+    }
+}
+
+/* Calculate *X + *Y exactly, storing the high part in *X (rounded to
+   nearest) and the low part in *Y.  It is given that |X| >= |Y|.  */
+
+static void
+add_split_ext (ext_val *x, ext_val *y)
+{
+  int xexp = x->exp, yexp = y->exp;
+  if (y->val == 0 || xexp - yexp > 53)
+    return;
+  double hi = x->val;
+  double lo = __scalbn (y->val, yexp - xexp);
+  add_split (&hi, &lo, hi, lo);
+  store_ext_val (x, hi);
+  if (hi != 0)
+    x->exp += xexp;
+  store_ext_val (y, lo);
+  if (lo != 0)
+    y->exp += xexp;
+}
 
 long double
 __fmal (long double x, long double y, long double z)
 {
-	/* An IBM long double 128 is really just 2 IEEE64 doubles, and in
-	 * the case of inf/nan only the first double counts. So we use the
-	 * (double) cast to avoid any data movement.   */
-       if ((isfinite ((double)x) && isfinite ((double)y)) && isinf ((double)z))
-               return (z);
-
-       /* If z is zero and x are y are nonzero, compute the result
-	  as x * y to avoid the wrong sign of a zero result if x * y
-	  underflows to 0.  */
-       if (z == 0 && x != 0 && y != 0)
-	 return x * y;
-
-       return (x * y) + z;
+  double xhi, xlo, yhi, ylo, zhi, zlo;
+  int64_t hx, hy, hz;
+  int xexp, yexp, zexp;
+  double scale_val;
+  int scale_exp;
+  ldbl_unpack (x, &xhi, &xlo);
+  EXTRACT_WORDS64 (hx, xhi);
+  xexp = (hx & 0x7ff0000000000000LL) >> 52;
+  ldbl_unpack (y, &yhi, &ylo);
+  EXTRACT_WORDS64 (hy, yhi);
+  yexp = (hy & 0x7ff0000000000000LL) >> 52;
+  ldbl_unpack (z, &zhi, &zlo);
+  EXTRACT_WORDS64 (hz, zhi);
+  zexp = (hz & 0x7ff0000000000000LL) >> 52;
+
+  /* If z is Inf or NaN, but x and y are finite, avoid any exceptions
+     from computing x * y.  */
+  if (zexp == 0x7ff && xexp != 0x7ff && yexp != 0x7ff)
+    return (z + x) + y;
+
+  /* If z is zero and x are y are nonzero, compute the result as x * y
+     to avoid the wrong sign of a zero result if x * y underflows to
+     0.  */
+  if (z == 0 && x != 0 && y != 0)
+    return x * y;
+
+  /* If x or y or z is Inf/NaN, or if x * y is zero, compute as x * y
+     + z.  */
+  if (xexp == 0x7ff || yexp == 0x7ff || zexp == 0x7ff
+      || x == 0 || y == 0)
+    return (x * y) + z;
+
+  {
+    SET_RESTORE_ROUND (FE_TONEAREST);
+
+    ext_val vals[10];
+    store_ext_val (&vals[0], zhi);
+    store_ext_val (&vals[1], zlo);
+    mul_ext_val (&vals[2], &vals[3], xhi, yhi);
+    mul_ext_val (&vals[4], &vals[5], xhi, ylo);
+    mul_ext_val (&vals[6], &vals[7], xlo, yhi);
+    mul_ext_val (&vals[8], &vals[9], xlo, ylo);
+    qsort (vals, 10, sizeof (ext_val), compare);
+    /* Add up the values so that each element of VALS has absolute
+       value at most equal to the last set bit of the next nonzero
+       element.  */
+    for (size_t i = 0; i <= 8; i++)
+      {
+	add_split_ext (&vals[i + 1], &vals[i]);
+	qsort (vals + i + 1, 9 - i, sizeof (ext_val), compare);
+      }
+    /* Add up the values in the other direction, so that each element
+       of VALS has absolute value less than 5ulp of the next
+       value.  */
+    size_t dstpos = 9;
+    for (size_t i = 1; i <= 9; i++)
+      {
+	if (vals[dstpos].val == 0)
+	  {
+	    vals[dstpos] = vals[9 - i];
+	    vals[9 - i].val = 0;
+	    vals[9 - i].exp = 0;
+	  }
+	else
+	  {
+	    add_split_ext (&vals[dstpos], &vals[9 - i]);
+	    if (vals[9 - i].val != 0)
+	      {
+		if (9 - i < dstpos - 1)
+		  {
+		    vals[dstpos - 1] = vals[9 - i];
+		    vals[9 - i].val = 0;
+		    vals[9 - i].exp = 0;
+		  }
+		dstpos--;
+	      }
+	  }
+      }
+    /* If the result is an exact zero, it results from adding two
+       values with opposite signs; recompute in the original rounding
+       mode.  */
+    if (vals[9].val == 0)
+      goto zero_out;
+    /* Adding the top three values will now give a result as accurate
+       as the underlying long double arithmetic.  */
+    add_split_ext (&vals[9], &vals[8]);
+    if (compare (&vals[8], &vals[7]) < 0)
+      {
+	ext_val tmp = vals[7];
+	vals[7] = vals[8];
+	vals[8] = tmp;
+      }
+    add_split_ext (&vals[8], &vals[7]);
+    add_split_ext (&vals[9], &vals[8]);
+    if (vals[9].exp > DBL_MAX_EXP || vals[9].exp < DBL_MIN_EXP)
+      {
+	/* Overflow or underflow, with the result depending on the
+	   original rounding mode, but not on the low part computed
+	   here.  */
+	scale_val = vals[9].val;
+	scale_exp = vals[9].exp;
+	goto scale_out;
+      }
+    double hi = __scalbn (vals[9].val, vals[9].exp);
+    double lo = __scalbn (vals[8].val, vals[8].exp);
+    /* It is possible that the low part became subnormal and was
+       rounded so that the result is no longer canonical.  */
+    ldbl_canonicalize (&hi, &lo);
+    long double ret = ldbl_pack (hi, lo);
+    math_check_force_underflow (ret);
+    return ret;
+  }
+
+ scale_out:
+  scale_val = math_opt_barrier (scale_val);
+  scale_val = __scalbn (scale_val, scale_exp);
+  if (fabs (scale_val) == DBL_MAX)
+    return __copysignl (LDBL_MAX, scale_val);
+  math_check_force_underflow (scale_val);
+  return scale_val;
+
+ zero_out:;
+  double zero = 0.0;
+  zero = math_opt_barrier (zero);
+  return zero - zero;
 }
 #if IS_IN (libm)
 long_double_symbol (libm, __fmal, fmal);