* [PATCH 2/2] added auxiliary routine reduce_aux
@ 2021-03-31 19:27 Paul Zimmermann
0 siblings, 0 replies; only message in thread
From: Paul Zimmermann @ 2021-03-31 19:27 UTC (permalink / raw)
To: libc-alpha
---
sysdeps/ieee754/flt-32/reduce_aux.h | 64 +++++++++++++++++++++++++++++
1 file changed, 64 insertions(+)
create mode 100644 sysdeps/ieee754/flt-32/reduce_aux.h
diff --git a/sysdeps/ieee754/flt-32/reduce_aux.h b/sysdeps/ieee754/flt-32/reduce_aux.h
new file mode 100644
index 0000000000..394721a9fd
--- /dev/null
+++ b/sysdeps/ieee754/flt-32/reduce_aux.h
@@ -0,0 +1,64 @@
+/* Auxiliary routine for the Bessel functions (j0f, y0f, j1f, y1f).
+ Copyright (C) 2021 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/>. */
+
+#ifndef _MATH_REDUCE_AUX_H
+#define _MATH_REDUCE_AUX_H
+
+#include <math.h>
+#include <math_private.h>
+#include <s_sincosf.h>
+
+/* Return h and update n such that:
+ Now x - pi/4 - alpha = h + n*pi/2 mod (2*pi). */
+static inline double
+reduce_aux (float x, int *n, double alpha)
+{
+ double h;
+ h = reduce_large (asuint (x), n);
+ /* Now |x| = h+n*pi/2 mod 2*pi. */
+ /* Recover sign. */
+ if (x < 0)
+ {
+ h = -h;
+ *n = -*n;
+ }
+ /* Subtract pi/4. */
+ double piover2 = 0xc.90fdaa22168cp-3;
+ if (h >= 0)
+ h -= piover2 / 2;
+ else
+ {
+ h += piover2 / 2;
+ (*n) --;
+ }
+ /* Subtract alpha and reduce if needed mod pi/2. */
+ h -= alpha;
+ if (h > piover2)
+ {
+ h -= piover2;
+ (*n) ++;
+ }
+ else if (h < -piover2)
+ {
+ h += piover2;
+ (*n) --;
+ }
+ return h;
+}
+
+#endif
--
2.30.2
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