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Re: convertFormat and signaling NaN



On 2011-03-13 17:24:57 -0700, Dan Zuras IEEE wrote:
      While it is true that convertFormat doesn't preclude
      formatOf being the same format as source, it is also
      true that it does not include it.

What do you mean by "does not include it"?

The IEEE 754 standard says: "Implementations shall provide the
following formatOf conversion operations from all supported
floating-point formats to all supported floating-point formats,
as well as [...]".

So, if some format, e.g. binary64, is supported, then
binary64 convertFormat(binary64) shall be provided.

[...]
      Further, is it not in keeping with the character
      of C that syntax that leads to null operations are
      permitted to be interpreted as removed?  Thus,
      -(-x) == x, or -(x - y) == y - x, et al.

No. F.8.2 says that such transformations are invalid if they
can change the result. It even mentions the case of signaling
NaNs:

  317) Strict support for signaling NaNs -- not required by this
       specification -- would invalidate these and other
       transformations that remove arithmetic operators.

I recall the context is strict support for signaling NaNs.

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