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Re: Halfway cases for binary-to-decimal conversion in IEEE 754-1985
On 2009-04-09 05:48:11 -0700, Dan Zuras IEEE wrote:
Look more closely at the 1985 text & you will discover that
binary <--> decimal conversion is only required to be correct
to 1.5 ULPs. The reason for this is that efficient algorithms
were not yet known at the time.
This is not what I read:
Conversions shall be correctly rounded as specified in Section 4 for
^^^^^^^^^^^^^^^^^
operands lying within the ranges specified in Table 3.
But this hardly matters because the 1985 text was obsoleted
when the 2008 text was published.
No, this matters, because e.g. the language standards may remain
linked to IEEE 754-1985. For instance, this is the case of the
ISO C99 standard (with its annex F), which has not been revised
yet. If IEEE 754-2008 has stricter requirements than the 1985
version, a conforming C99 implementation will not magically
become non-conforming just because IEEE 754-2008 has obsoleted
the 1985 version.
--
Vincent Lefèvre <vincent@xxxxxxxxxx> - Web: <http://www.vinc17.org/>
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Work: CR INRIA - computer arithmetic / Arenaire project (LIP, ENS-Lyon)