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+/* 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 */