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[Bug math/13932] dbl-64 pow unexpectedly slow for some inputs
- From: "cvs-commit at gcc dot gnu.org" <sourceware-bugzilla at sourceware dot org>
- To: glibc-bugs at sourceware dot org
- Date: Mon, 12 Feb 2018 10:48:33 +0000
- Subject: [Bug math/13932] dbl-64 pow unexpectedly slow for some inputs
- Auto-submitted: auto-generated
- References: <bug-13932-131@http.sourceware.org/bugzilla/>
https://sourceware.org/bugzilla/show_bug.cgi?id=13932
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https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=c3d466cba1692708a19c6ff829d0386c83a0c6e5
commit c3d466cba1692708a19c6ff829d0386c83a0c6e5
Author: Wilco Dijkstra <wdijkstr@arm.com>
Date: Mon Feb 12 10:42:42 2018 +0000
Remove slow paths from pow
Remove the slow paths from pow. Like several other double precision math
functions, pow is exactly rounded. This is not required from math
functions
and causes major overheads as it requires multiple fallbacks using higher
precision arithmetic if a result is close to 0.5ULP. Ridiculous slowdowns
of up to 100000x have been reported when the highest precision path
triggers.
All GLIBC math tests pass on AArch64 and x64 (with ULP of pow set to 1).
The worst case error is ~0.506ULP. A simple test over a few hundred
million
values shows pow is 10% faster on average. This fixes BZ #13932.
[BZ #13932]
* sysdeps/ieee754/dbl-64/uexp.h (err_1): Remove.
* benchtests/pow-inputs: Update comment for slow path cases.
* manual/probes.texi (slowpow_p10): Delete removed probe.
(slowpow_p10): Likewise.
* math/Makefile: Remove halfulp.c and slowpow.c.
* sysdeps/aarch64/libm-test-ulps: Set ULP of pow to 1.
* sysdeps/generic/math_private.h (__exp1): Remove error argument.
(__halfulp): Remove.
(__slowpow): Remove.
* sysdeps/i386/fpu/halfulp.c: Delete file.
* sysdeps/i386/fpu/slowpow.c: Likewise.
* sysdeps/ia64/fpu/halfulp.c: Likewise.
* sysdeps/ia64/fpu/slowpow.c: Likewise.
* sysdeps/ieee754/dbl-64/e_exp.c (__exp1): Remove error argument,
improve comments and add error analysis.
* sysdeps/ieee754/dbl-64/e_pow.c (__ieee754_pow): Add error analysis.
(power1): Remove function:
(log1): Remove error argument, add error analysis.
(my_log2): Remove function.
* sysdeps/ieee754/dbl-64/halfulp.c: Delete file.
* sysdeps/ieee754/dbl-64/slowpow.c: Likewise.
* sysdeps/m68k/m680x0/fpu/halfulp.c: Likewise.
* sysdeps/m68k/m680x0/fpu/slowpow.c: Likewise.
* sysdeps/powerpc/power4/fpu/Makefile: Remove CPPFLAGS-slowpow.c.
* sysdeps/x86_64/fpu/libm-test-ulps: Set ULP of pow to 1.
* sysdeps/x86_64/fpu/multiarch/Makefile: Remove slowpow-fma.c,
slowpow-fma4.c, halfulp-fma.c, halfulp-fma4.c.
* sysdeps/x86_64/fpu/multiarch/e_pow-fma.c (__slowpow): Remove define.
* sysdeps/x86_64/fpu/multiarch/e_pow-fma4.c (__slowpow): Likewise.
* sysdeps/x86_64/fpu/multiarch/halfulp-fma.c: Delete file.
* sysdeps/x86_64/fpu/multiarch/halfulp-fma4.c: Likewise.
* sysdeps/x86_64/fpu/multiarch/slowpow-fma.c: Likewise.
* sysdeps/x86_64/fpu/multiarch/slowpow-fma4.c: Likewise.
-----------------------------------------------------------------------
Summary of changes:
ChangeLog | 37 ++++++
benchtests/pow-inputs | 6 +-
manual/probes.texi | 16 ---
math/Makefile | 4 +-
sysdeps/aarch64/libm-test-ulps | 2 +
sysdeps/generic/math_private.h | 4 +-
sysdeps/i386/fpu/halfulp.c | 1 -
sysdeps/i386/fpu/slowpow.c | 1 -
sysdeps/ia64/fpu/halfulp.c | 1 -
sysdeps/ia64/fpu/slowpow.c | 1 -
sysdeps/ieee754/dbl-64/e_exp.c | 42 +++----
sysdeps/ieee754/dbl-64/e_pow.c | 172 ++++-----------------------
sysdeps/ieee754/dbl-64/halfulp.c | 152 -----------------------
sysdeps/ieee754/dbl-64/slowpow.c | 125 -------------------
sysdeps/ieee754/dbl-64/uexp.h | 2 +-
sysdeps/m68k/m680x0/fpu/halfulp.c | 1 -
sysdeps/m68k/m680x0/fpu/slowpow.c | 1 -
sysdeps/powerpc/power4/fpu/Makefile | 1 -
sysdeps/x86_64/fpu/libm-test-ulps | 2 +
sysdeps/x86_64/fpu/multiarch/Makefile | 12 +--
sysdeps/x86_64/fpu/multiarch/e_pow-fma.c | 1 -
sysdeps/x86_64/fpu/multiarch/e_pow-fma4.c | 1 -
sysdeps/x86_64/fpu/multiarch/halfulp-fma.c | 4 -
sysdeps/x86_64/fpu/multiarch/halfulp-fma4.c | 4 -
sysdeps/x86_64/fpu/multiarch/slowpow-fma.c | 11 --
sysdeps/x86_64/fpu/multiarch/slowpow-fma4.c | 11 --
26 files changed, 90 insertions(+), 525 deletions(-)
delete mode 100644 sysdeps/i386/fpu/halfulp.c
delete mode 100644 sysdeps/i386/fpu/slowpow.c
delete mode 100644 sysdeps/ia64/fpu/halfulp.c
delete mode 100644 sysdeps/ia64/fpu/slowpow.c
delete mode 100644 sysdeps/ieee754/dbl-64/halfulp.c
delete mode 100644 sysdeps/ieee754/dbl-64/slowpow.c
delete mode 100644 sysdeps/m68k/m680x0/fpu/halfulp.c
delete mode 100644 sysdeps/m68k/m680x0/fpu/slowpow.c
delete mode 100644 sysdeps/x86_64/fpu/multiarch/halfulp-fma.c
delete mode 100644 sysdeps/x86_64/fpu/multiarch/halfulp-fma4.c
delete mode 100644 sysdeps/x86_64/fpu/multiarch/slowpow-fma.c
delete mode 100644 sysdeps/x86_64/fpu/multiarch/slowpow-fma4.c
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