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Re: IEEE128 binary float to decimal float conversion routines
- From: Joseph Myers <joseph at codesourcery dot com>
- To: "Paul E. Murphy" <murphyp at linux dot vnet dot ibm dot com>
- Cc: "libc-alpha at sourceware dot org" <libc-alpha at sourceware dot org>, Steve Munroe <sjmunroe at us dot ibm dot com>, Tulio Magno Quites Machado Filho <tuliom at linux dot vnet dot ibm dot com>, Michael R Meissner <mrmeissn at us dot ibm dot com>
- Date: Mon, 16 Nov 2015 18:24:37 +0000
- Subject: Re: IEEE128 binary float to decimal float conversion routines
- Authentication-results: sourceware.org; auth=none
- References: <564A16D5 dot 3020105 at linux dot vnet dot ibm dot com>
On Mon, 16 Nov 2015, Paul E. Murphy wrote:
> Hi Joseph,
>
> I think there may have been a question as to where the
> conversion routines between IEEE 128 binary float and
> decimal float should live.
>
> Observing existing precedent and machinery, I think
> the appropriate place to house them is within libdfp.
I think existing practice is that there's a copy of such functions in
libgcc and another copy in libdfp - and maybe the libdfp version supports
exceptions and rounding modes (software or hardware) but the libgcc
version doesn't?
The BID conversions between binary and decimal float involve several MB of
tables (whereas libgcc DPD conversions go via strings). Several MB of
tables are not of course needed; if doing correctly-rounded conversions
(required for IEEE 754 conformance) there's a speed/space trade-off in how
much precomputed data you use versus how much computation you do at
runtime, and it's up to you what you think the right trade-off for powerpc
is.
--
Joseph S. Myers
joseph@codesourcery.com