[1/9] Auxiliary function for reduction modulo 2*pi.
Commit Message
---
sysdeps/ieee754/flt-32/reduce_aux.c | 55 +++++++++++++++++++++++++++++
1 file changed, 55 insertions(+)
create mode 100644 sysdeps/ieee754/flt-32/reduce_aux.c
Comments
On 19/03/2021 12:06, Paul Zimmermann wrote:
> ---
> sysdeps/ieee754/flt-32/reduce_aux.c | 55 +++++++++++++++++++++++++++++
I think it is better to move it to a header with proper include guards,
since it is usual way of defining internal static inline functions (just
rename to reduce_aux.h and add #ifndef guards).
I also tried to move it to its own TU to see what kind of code size gain
it would yield. For aarch64 I am seeing a reduction of 488 bytes, so if
you might consider it if this is not a performance-wise routine.
LGTM with the header change.
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
> 1 file changed, 55 insertions(+)
> create mode 100644 sysdeps/ieee754/flt-32/reduce_aux.c
>
> diff --git a/sysdeps/ieee754/flt-32/reduce_aux.c b/sysdeps/ieee754/flt-32/reduce_aux.c
> new file mode 100644
> index 0000000000..412b4d22cb
> --- /dev/null
> +++ b/sysdeps/ieee754/flt-32/reduce_aux.c
> @@ -0,0 +1,55 @@
> +/* 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/>. */
> +
> +/* 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;
> +}
>
thank you Adhemerval for your review. I have just submitted a cumulated patch
of this series (I spend too much time maintaining such a series of patches
when some to need to be updated and some not).
The only changes are the following ones.
For reduce_aux.c: I have moved it to a file reduce_aux.h with include guards
(btw I noticed that s_sincosf.h has not include guards).
I have added your patch with xfail entries for powerpc (it is strange I did
not hit that since I've tested on powerpc too).
Best regards,
Paul
On 30/03/2021 14:24, Paul Zimmermann wrote:
> thank you Adhemerval for your review. I have just submitted a cumulated patch
> of this series (I spend too much time maintaining such a series of patches
> when some to need to be updated and some not).
>
> The only changes are the following ones.
>
> For reduce_aux.c: I have moved it to a file reduce_aux.h with include guards
> (btw I noticed that s_sincosf.h has not include guards).
>
> I have added your patch with xfail entries for powerpc (it is strange I did
> not hit that since I've tested on powerpc too).
Right, so this new patch supersedes this whole set?
new file mode 100644
@@ -0,0 +1,55 @@
+/* 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/>. */
+
+/* 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;
+}