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authorPaul E. Murphy <murphyp@linux.vnet.ibm.com>2016-08-08 15:58:28 -0500
committerPaul E. Murphy <murphyp@linux.vnet.ibm.com>2016-08-19 11:29:43 -0500
commit4482ff226e4b286ab171f3c5841ae1f7e61780cd (patch)
tree69bf06744f290b3656ad238c0b5dd700c850f9e9 /math/mul_splitl.h
parent01ee387015a2075c45a4e1ad45d39e50b5a6d40b (diff)
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Merge common usage of mul_split function
A number of files share identical code for the
mul_split function.

This moves the duplicated function mul_split into its
own header, and refactors the fma usage into a single
selection macro.  Likewise, mul_split when used by a
long double implementation is renamed mul_splitl for
clarity.
Diffstat (limited to 'math/mul_splitl.h')
-rw-r--r--math/mul_splitl.h50
1 files changed, 50 insertions, 0 deletions
diff --git a/math/mul_splitl.h b/math/mul_splitl.h
new file mode 100644
index 0000000000..8a39ce0553
--- /dev/null
+++ b/math/mul_splitl.h
@@ -0,0 +1,50 @@
+/* Compute full X * Y for long double type.
+   Copyright (C) 2013-2016 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/>.  */
+
+#ifndef _MUL_SPLITL_H
+#define _MUL_SPLITL_H
+
+#include <float.h>
+
+/* Calculate X * Y exactly and store the result in *HI + *LO.  It is
+   given that the values are small enough that no overflow occurs and
+   large enough (or zero) that no underflow occurs.  */
+
+static inline void
+mul_splitl (long double *hi, long double *lo, long double x, long double y)
+{
+#ifdef __FP_FAST_FMAL
+  /* Fast built-in fused multiply-add.  */
+  *hi = x * y;
+  *lo = __builtin_fmal (x, y, -*hi);
+#else
+  /* Apply Dekker's algorithm.  */
+  *hi = x * y;
+# define C ((1LL << (LDBL_MANT_DIG + 1) / 2) + 1)
+  long double x1 = x * C;
+  long double y1 = y * C;
+# undef C
+  x1 = (x - x1) + x1;
+  y1 = (y - y1) + y1;
+  long double x2 = x - x1;
+  long double y2 = y - y1;
+  *lo = (((x1 * y1 - *hi) + x1 * y2) + x2 * y1) + x2 * y2;
+#endif
+}
+
+#endif /* _MUL_SPLITL_H */