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Re: [PATCH] Increase internal precision of ldbl-128ibm decimal printf
- From: "Paul E. Murphy" <murphyp at linux dot vnet dot ibm dot com>
- To: Joseph Myers <joseph at codesourcery dot com>
- Cc: "libc-alpha at sourceware dot org" <libc-alpha at sourceware dot org>, Tulio Magno Quites Machado Filho <tuliom at linux dot vnet dot ibm dot com>
- Date: Thu, 17 Mar 2016 18:13:49 -0500
- Subject: Re: [PATCH] Increase internal precision of ldbl-128ibm decimal printf
- Authentication-results: sourceware.org; auth=none
- References: <56EB246E dot 4050504 at linux dot vnet dot ibm dot com> <alpine dot DEB dot 2 dot 10 dot 1603172212150 dot 18027 at digraph dot polyomino dot org dot uk>
On 03/17/2016 05:16 PM, Joseph Myers wrote:
> On Thu, 17 Mar 2016, Paul E. Murphy wrote:
>
>> When the signs differ, the precision of the conversion
>> could drop below 106 bits. This strategy is
>> identical to the hexadecimal variant.
>
> I assume this was user-visible in a release, in which case it should have
> a bug filed in Bugzilla (if it doesn't already have one - I take it this
> is distinct from bug 5268?).
>
> It should also have a testcase included in the patch (there are several
> tests in sysdeps/ieee754/ldbl-128ibm already for issues specific to this
> format - various of which use unions to test issues that can't be tested
> simply with 106-bit inputs GCC can represent, or where it's necessary to
> examine the two halves of a long double result separately).
>
This came up internally. I think it is similar, the comments would indicate
it is a 1 bit internal precision loss which this patch does address.
I will figure out how to update the tests to catch this, and give the magic
shift amount a name.
Thanks,
Paul