[PATCH] x86_64: Add log2 with FMA

[PATCH] x86_64: Add log2 with FMA

[H.J. Lu]

On Skylake, it improves log2 bench performance by:

        Before       After     Improvement
max     208.779      63.827       69%
min     9.977        6.55         34%
mean    10.366       6.8191       34%
---
 sysdeps/x86_64/fpu/multiarch/Makefile     |  2 ++
 sysdeps/x86_64/fpu/multiarch/e_log2-fma.c |  3 ++
 sysdeps/x86_64/fpu/multiarch/e_log2.c     | 43 +++++++++++++++++++++++
 3 files changed, 48 insertions(+)
 create mode 100644 sysdeps/x86_64/fpu/multiarch/e_log2-fma.c
 create mode 100644 sysdeps/x86_64/fpu/multiarch/e_log2.c

diff --git a/sysdeps/x86_64/fpu/multiarch/Makefile b/sysdeps/x86_64/fpu/multiarch/Makefile
index e37e488c37..f773255721 100644
--- a/sysdeps/x86_64/fpu/multiarch/Makefile
+++ b/sysdeps/x86_64/fpu/multiarch/Makefile
@@ -34,6 +34,7 @@ libm-sysdep_routines += \
   e_atan2-fma \
   e_exp-fma \
   e_log-fma \
+  e_log2-fma \
   e_pow-fma \
   s_atan-fma \
   s_sin-fma \
@@ -45,6 +46,7 @@ CFLAGS-e_asin-fma.c = -mfma -mavx2
 CFLAGS-e_atan2-fma.c = -mfma -mavx2
 CFLAGS-e_exp-fma.c = -mfma -mavx2
 CFLAGS-e_log-fma.c = -mfma -mavx2
+CFLAGS-e_log2-fma.c = -mfma -mavx2
 CFLAGS-e_pow-fma.c = -mfma -mavx2
 CFLAGS-s_atan-fma.c = -mfma -mavx2
 CFLAGS-s_sin-fma.c = -mfma -mavx2
diff --git a/sysdeps/x86_64/fpu/multiarch/e_log2-fma.c b/sysdeps/x86_64/fpu/multiarch/e_log2-fma.c
new file mode 100644
index 0000000000..9fbebc1b47
--- /dev/null
+++ b/sysdeps/x86_64/fpu/multiarch/e_log2-fma.c
@@ -0,0 +1,3 @@
+#define __log2 __log2_fma
+
+#include <sysdeps/ieee754/dbl-64/e_log2.c>
diff --git a/sysdeps/x86_64/fpu/multiarch/e_log2.c b/sysdeps/x86_64/fpu/multiarch/e_log2.c
new file mode 100644
index 0000000000..c0320caf36
--- /dev/null
+++ b/sysdeps/x86_64/fpu/multiarch/e_log2.c
@@ -0,0 +1,43 @@
+/* Multiple versions of log2.
+   Copyright (C) 2023 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 <libm-alias-double.h>
+#include <libm-alias-finite.h>
+
+extern double __redirect_log2 (double);
+
+#define SYMBOL_NAME log2
+#include "ifunc-fma.h"
+
+libc_ifunc_redirected (__redirect_log2, __log2, IFUNC_SELECTOR ());
+
+#ifdef SHARED
+__hidden_ver1 (__log2, __GI___log2, __redirect_log2)
+  __attribute__ ((visibility ("hidden")));
+
+versioned_symbol (libm, __ieee754_log2, log2, GLIBC_2_29);
+libm_alias_double_other (__log2, log2)
+#else
+libm_alias_double (__log2, log2)
+#endif
+
+strong_alias (__log2, __ieee754_log2)
+libm_alias_finite (__log2, __log2)
+
+#define __log2 __log2_sse2
+#include <sysdeps/ieee754/dbl-64/e_log2.c>
-- 
2.41.0

Re: [PATCH] x86_64: Add log2 with FMA

[Noah Goldstein]

On Thu, Aug 10, 2023 at 1:24 PM H.J. Lu via Libc-alpha
<libc-alpha@sourceware.org> wrote:
>
> On Skylake, it improves log2 bench performance by:
>
>         Before       After     Improvement
> max     208.779      63.827       69%
> min     9.977        6.55         34%
> mean    10.366       6.8191       34%
> ---
>  sysdeps/x86_64/fpu/multiarch/Makefile     |  2 ++
>  sysdeps/x86_64/fpu/multiarch/e_log2-fma.c |  3 ++
>  sysdeps/x86_64/fpu/multiarch/e_log2.c     | 43 +++++++++++++++++++++++
>  3 files changed, 48 insertions(+)
>  create mode 100644 sysdeps/x86_64/fpu/multiarch/e_log2-fma.c
>  create mode 100644 sysdeps/x86_64/fpu/multiarch/e_log2.c
>
> diff --git a/sysdeps/x86_64/fpu/multiarch/Makefile b/sysdeps/x86_64/fpu/multiarch/Makefile
> index e37e488c37..f773255721 100644
> --- a/sysdeps/x86_64/fpu/multiarch/Makefile
> +++ b/sysdeps/x86_64/fpu/multiarch/Makefile
> @@ -34,6 +34,7 @@ libm-sysdep_routines += \
>    e_atan2-fma \
>    e_exp-fma \
>    e_log-fma \
> +  e_log2-fma \
>    e_pow-fma \
>    s_atan-fma \
>    s_sin-fma \
> @@ -45,6 +46,7 @@ CFLAGS-e_asin-fma.c = -mfma -mavx2
>  CFLAGS-e_atan2-fma.c = -mfma -mavx2
>  CFLAGS-e_exp-fma.c = -mfma -mavx2
>  CFLAGS-e_log-fma.c = -mfma -mavx2
> +CFLAGS-e_log2-fma.c = -mfma -mavx2
>  CFLAGS-e_pow-fma.c = -mfma -mavx2
>  CFLAGS-s_atan-fma.c = -mfma -mavx2
>  CFLAGS-s_sin-fma.c = -mfma -mavx2
> diff --git a/sysdeps/x86_64/fpu/multiarch/e_log2-fma.c b/sysdeps/x86_64/fpu/multiarch/e_log2-fma.c
> new file mode 100644
> index 0000000000..9fbebc1b47
> --- /dev/null
> +++ b/sysdeps/x86_64/fpu/multiarch/e_log2-fma.c
> @@ -0,0 +1,3 @@
> +#define __log2 __log2_fma
> +
> +#include <sysdeps/ieee754/dbl-64/e_log2.c>
> diff --git a/sysdeps/x86_64/fpu/multiarch/e_log2.c b/sysdeps/x86_64/fpu/multiarch/e_log2.c
> new file mode 100644
> index 0000000000..c0320caf36
> --- /dev/null
> +++ b/sysdeps/x86_64/fpu/multiarch/e_log2.c
> @@ -0,0 +1,43 @@
> +/* Multiple versions of log2.
> +   Copyright (C) 2023 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 <libm-alias-double.h>
> +#include <libm-alias-finite.h>
> +
> +extern double __redirect_log2 (double);
> +
> +#define SYMBOL_NAME log2
> +#include "ifunc-fma.h"
> +
> +libc_ifunc_redirected (__redirect_log2, __log2, IFUNC_SELECTOR ());
> +
> +#ifdef SHARED
> +__hidden_ver1 (__log2, __GI___log2, __redirect_log2)
> +  __attribute__ ((visibility ("hidden")));
> +
> +versioned_symbol (libm, __ieee754_log2, log2, GLIBC_2_29);
> +libm_alias_double_other (__log2, log2)
> +#else
> +libm_alias_double (__log2, log2)
> +#endif
> +
> +strong_alias (__log2, __ieee754_log2)
> +libm_alias_finite (__log2, __log2)
> +
> +#define __log2 __log2_sse2
> +#include <sysdeps/ieee754/dbl-64/e_log2.c>
> --
> 2.41.0
>

LGTM

Re: [PATCH] x86_64: Add log2 with FMA

[Paul Zimmermann]

       Hi H.J.,

> On Skylake, it improves log2 bench performance by:
> 
>         Before       After     Improvement
> max     208.779      63.827       69%
> min     9.977        6.55         34%
> mean    10.366       6.8191       34%

for what concerns accuracy, after a limited search, I get a small improvement
for the largest known error. It was 0.554114 ulp before (obtained for
x=0x1.0b53197bd66c8p+0), and I find 0.547517 ulp now (obtained for
x=0x1.140c8ac38f327p+0).

Paul