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Re: Question about the highly optimized aspects of libc implementation
- From: Will Hawkins <whh8b at virginia dot edu>
- To: "Carlos O'Donell" <carlos at redhat dot com>, siddhesh dot poyarekar at gmail dot com
- Cc: libc-help at sourceware dot org
- Date: Thu, 30 Nov 2017 02:00:38 -0500
- Subject: Re: Question about the highly optimized aspects of libc implementation
- Authentication-results: sourceware.org; auth=none
- References: <CAE+MWFsT5vu4yW0zDKgyinZky=2s-i2wzK7N-fnKuQP0kGQ_Bw@mail.gmail.com> <firstname.lastname@example.org>
Mr. O' Donell and Poyarekar,
Forgive the top-posting but I just wanted to quickly thank both of
your for your answers! This is exactly the type of information that I
was hoping to gather. Thank you again!
On Thu, Nov 30, 2017 at 1:56 AM, Carlos O'Donell <email@example.com> wrote:
> On 11/29/2017 10:47 PM, Will Hawkins wrote:
>> I've been digging through the glibc implementation and looking for
>> examples of where compiler directives or hand-written assembly have
>> been used to improve performance at the "expense" of standards or
> Let me address the "standards" side of this...
> No such thing exists and has a public interface that conforming programs
> can call. Such things may exist internal to glibc, but then we have
> control over the API/ABI and can do what we want.
> We have some functions which have standards for them, but for which
> we don't follow the standard because Linux did it one way and
> that's the only supportable way e.g. group scheduling etc.
> Let me address the "conventions" side of this...
> The entire math library has "cheats" which would be assembly implementations
> that have lower accuracy bounds. We have generally tended to remove these
> since we want a certain uniform level of accuracy for all the math functions
> where possible. One example was the removal of x86 sincos hardware support
> for the generic sin/cos support because the x86 hardware version is not
> accurate enough (poor range reduction).
> Does that answer your question?