Add nextup and nextdown math functions

TS 18661 adds nextup and nextdown functions alongside nextafter to provide
support for float128 equivalent to it.  This patch adds nextupl, nextup,
nextupf, nextdownl, nextdown and nextdownf to libm before float128 support.

The nextup functions return the next representable value in the direction of
positive infinity and the nextdown functions return the next representable
value in the direction of negative infinity.  These are currently enabled
as GNU extensions.

1 files changed, 78 insertions, 0 deletions

diff --git a/sysdeps/ieee754/ldbl-128ibm/s_nextupl.c b/sysdeps/ieee754/ldbl-128ibm/s_nextupl.c
new file mode 100644
index 0000000..2a4fae7
--- /dev/null
+++ b/sysdeps/ieee754/ldbl-128ibm/s_nextupl.c
@@ -0,0 +1,78 @@
+/* Return the least floating-point number greater than X.
+   Copyright (C) 2016 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <math.h>
+#include <math_private.h>
+#include <math_ldbl_opt.h>
+
+/* Return the least floating-point number greater than X.  */
+long double
+__nextupl (long double x)
+{
+  int64_t hx, ihx, lx;
+  double xhi, xlo, yhi;
+
+  ldbl_unpack (x, &xhi, &xlo);
+  EXTRACT_WORDS64 (hx, xhi);
+  EXTRACT_WORDS64 (lx, xlo);
+  ihx = hx & 0x7fffffffffffffffLL;
+
+  if (ihx > 0x7ff0000000000000LL)	/* x is nan.  */
+    return x + x;		/* Signal the nan.  */
+  if (ihx == 0)
+    return LDBL_TRUE_MIN;
+
+  long double u;
+  if ((hx == 0x7fefffffffffffffLL) && (lx == 0x7c8ffffffffffffeLL))
+    return INFINITY;
+  if ((uint64_t) hx >= 0xfff0000000000000ULL)
+    {
+      u = -0x1.fffffffffffff7ffffffffffff8p+1023L;
+      return u;
+    }
+  if (ihx <= 0x0360000000000000LL)
+    {				/* x <= LDBL_MIN.  */
+      x += LDBL_TRUE_MIN;
+      if (x == 0.0L)		/* Handle negative LDBL_TRUE_MIN case.  */
+        x = -0.0L;
+      return x;
+    }
+  /* If the high double is an exact power of two and the low
+     double is the opposite sign, then 1ulp is one less than
+     what we might determine from the high double.  Similarly
+     if X is an exact power of two, and negative, because
+     making it a little larger will result in the exponent
+     decreasing by one and normalisation of the mantissa.   */
+  if ((hx & 0x000fffffffffffffLL) == 0
+      && ((lx != 0 && lx != 0x8000000000000000LL && (hx ^ lx) < 0)
+          || ((lx == 0 || lx == 0x8000000000000000LL) && hx < 0)))
+    ihx -= 1LL << 52;
+  if (ihx < (106LL << 52))
+    {				/* ulp will denormal.  */
+      INSERT_WORDS64 (yhi, ihx & (0x7ffLL << 52));
+      u = yhi * 0x1p-105;
+    }
+  else
+    {
+      INSERT_WORDS64 (yhi, (ihx & (0x7ffLL << 52)) - (105LL << 52));
+      u = yhi;
+    }
+  return x + u;
+}
+
+weak_alias (__nextupl, nextupl)