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Re: IEEE128 binary float to decimal float conversion routines
- From: Christoph Lauter <christoph dot lauter at lip6 dot fr>
- To: Joseph Myers <joseph at codesourcery dot com>, "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 23:08:14 +0100
- 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> <alpine dot DEB dot 2 dot 10 dot 1511161803500 dot 30498 at digraph dot polyomino dot org dot uk>
Hi everyone,
Joseph Myers wrote on 11/16/2015 07:24 PM:
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.
For what it's worth: some colleagues of mine and myself have recently
published a paper on exact binary-to-decimal conversions between all
IEEE754 formats, assuming BID as the encoding for decimal. None of the
algorithms we proposed uses a table larger that a couple of dozens of
kilobytes. Converting between binary and decimal FP with correct
rounding is essentially the same problem, so people might wish to have a
look at these results:
http://www.computer.org/csdl/trans/tc/preprint/07271015-abs.html
Best regards,
Christoph Lauter
--
Christoph Lauter
Maître de conférences - Associate Professor
Équipe PEQUAN - LIP6 - UPMC Paris 6
4, place Jussieu, 75252 Paris Cedex 05, 26-00/301
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