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Re: [PATCH] Sparc exp(), expf() performance improvement

• From: Patrick McGehearty <patrick dot mcgehearty at oracle dot com>
• To: Joseph Myers <joseph at codesourcery dot com>
• Cc: libc-alpha at sourceware dot org
• Date: Wed, 2 Aug 2017 18:35:08 -0500
• Subject: Re: [PATCH] Sparc exp(), expf() performance improvement
• Authentication-results: sourceware.org; auth=none
• References: <1501529969-96949-1-git-send-email-patrick.mcgehearty@oracle.com> <alpine.DEB.2.20.1707312058070.11716@digraph.polyomino.org.uk>

Apologies for the many earlier versions of this email.My fingers forgot I was in a mailer not an editor andevery time I typed "^S" to save my temporary version,the mailer did a send.This is the intended version of this note.- patrickOn 7/31/2017 4:06 PM, Joseph Myers wrote:

On Mon, 31 Jul 2017, Patrick McGehearty wrote:

     * sysdeps/sparc/configure.ac: manage -mcpu=niagara4 test     * sysdeps/sparc/configure: Regenerate

As far as I can see, niagara4 support was added to GCC in r178554(2011-09-05), so would have been in GCC 4.7.  The minimum GCC version forbuilding glibc is 4.9.  So this configure test, and any associatedconditionals in Makefiles or elsewhere, should not be necessary.

Internally I need to support some Oracle Linux releases which use gcc 4.4.7.

both the Oracle and sourceware versions.I'll simplify my patch for sourceware, omitting the test.Same applies to the use of#ifndef DBL_MINas DBL_MIN was not defined in older glibc/gcc trees.I'll remove the DBL_MIN def.

diff --git a/sysdeps/sparc/fpu/libm_endian.h b/sysdeps/sparc/fpu/libm_endian.hnew file mode 100644index 0000000..a49abcd--- /dev/null+++ b/sysdeps/sparc/fpu/libm_endian.h@@ -0,0 +1,32 @@+/*+   Contributed by Oracle Inc.+   Copyright (C) 2017 Free Software Foundation, Inc.

All new files should start with a descriptive comment on their first line,before the copyright notice.  "Contributed by" is no longer used;significant contributions can be mentioned in the NEWS file (as well as incontrib.texi).

+extern double exp (double);

No such declaration should be needed, since you're including <math.h>.

Ok, removed.

+extern double __ieee754_exp (double);

And this should come through math_private.h.

I'm not finding it in any math_private.h that I've checked.Do you mean I should put it in sysdeps/sparc/fpu/math_private.h?

+/*+ * For i = 0, ..., 66,+ *   TBL2[2*i] is a double precision number near (i+1)*2^-6, and

We don't use leading '*' on each line of a comment.

Fixed.

+static const double zC[] = {+  0.5,+  4.61662413084468283841e+01,/* 0x40471547, 0x652b82fe */+  2.16608493865351192653e-02,/* 0x3f962e42, 0xfee00000 */+  5.96317165397058656257e-12,/* 0x3d9a39ef, 0x35793c76 */

Please put a comment on each file-scope variable or function explainingits semantics.If you're commenting exact representations of floating-point numbers, I'dadvise writing them as C99 hex float constants instead of decimal (andthen omitting those comments) - generally I think hex float constants area good idea for any constants that have been computed to have someproperty (polynomial coefficients, etc.) and can't be expected to behuman-readable.

entry could slip by even extended testing procedures.On the other hand, I can readily change the zC table into the following:static const half       0.5;

...and add comments to the limit of my understanding of the algorithm.I am porting this code, not the original developer.I will make those changes.

+#ifndef DBL_MIN+#define DBL_MIN 2.2250738585072014E-308+#endif

Just include <float.h>.  No such #ifndef is then needed (and we useindentation inside #if, "# define" etc.).

will remove for sourceware version of code.

+#definehalfzC[0]+#defineinvln2_32zC[1]

It would be better to make each of these into a separate static constvariable with its own comment rather than defining an array full ofunrelated values.

will do.

Much the same comments apply to the float code.

I will make similar changes to float.

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  • Re: [PATCH] Sparc exp(), expf() performance improvement
    • From: Joseph Myers