Add a generic scalb implementation

This is a preparatory patch to enable building a _Float128
variant to ease reuse when building a _Float128 variant to
alias this long double only symbol.

Notably, stubs are added where missing to the native _Float128
sysdep dir to prevent building these newly templated variants
created inside the build directories.

Also noteworthy are the changes around LIBM_SVID_COMPAT.  These
changes are not intuitive.  The templated version is only
enabled when !LIBM_SVID_COMPAT, and the compat version is
predicated entirely on LIBM_SVID_COMPAT.  Thus, exactly one is
stubbed out entirely when building.  The nldbl scalb compat
files are updated to account for this.

Likewise, fixup the reuse of m68k's e_scalb{f,l}.c to include
it's override of e_scalb.c.  Otherwise, the search path finds
the templated copy in the build directory.  This could be
futher simplified by providing an overridden template, but I
lack the hardware to verify.

1 files changed, 57 insertions, 0 deletions

diff --git a/math/e_scalb_template.c b/math/e_scalb_template.c
new file mode 100644
index 0000000000..ed0508c7bf
--- /dev/null
+++ b/math/e_scalb_template.c
@@ -0,0 +1,57 @@
+/* Multiply by integral power of radix.
+
+   Copyright (C) 2011-2020 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
+   <https://www.gnu.org/licenses/>.  */
+
+#include <math.h>
+#include <math_private.h>
+#include <libm-alias-finite.h>
+
+static FLOAT
+__attribute__ ((noinline))
+invalid_fn (FLOAT x, FLOAT fn)
+{
+  if (M_SUF (rint) (fn) != fn)
+    return (fn - fn) / (fn - fn);
+  else if (fn > M_LIT (65000.0))
+    return M_SUF (__scalbn) (x, 65000);
+  else
+    return M_SUF (__scalbn) (x,-65000);
+}
+
+
+FLOAT
+M_DECL_FUNC (__ieee754_scalb) (FLOAT x, FLOAT fn)
+{
+  if (__glibc_unlikely (isnan (x)))
+    return x * fn;
+  if (__glibc_unlikely (!isfinite (fn)))
+    {
+      if (isnan (fn) || fn > M_LIT (0.0))
+	return x * fn;
+      if (x == M_LIT (0.0))
+	return x;
+      return x / -fn;
+    }
+  if (__glibc_unlikely (M_FABS (fn) >= M_LIT (0x1p31)
+			|| (FLOAT) (int) fn != fn))
+    return invalid_fn (x, fn);
+
+  return M_SCALBN (x, (int) fn);
+}
+declare_mgen_finite_alias (__ieee754_scalb, __scalb)