Re: A Level 2 query
Jürgen
On 9 Jun 2013, at 19:58, Jürgen Wolff von Gudenberg wrote:
> isn't that the problem with the extended 80bit format in the early processors ?
> AFAIK this has only caused some inconsistencies like due to double rounding. thre tightst enclosure is not found.
> so my answer is yes [(JDP) I assume you mean it should be a violation of 1788.]
That was in floating point, where inconsistencies (between compilers, or between optimisation levels of one compiler) can be extremely annoying. With intervals, you have containment and the effect, especially if done throughout a long expression, will be to get a tighter enclosure than you "expected". Is that really so annoying? Actually I tend to agree with you and am playing devil's advocate.
John
> Am 09.06.2013 17:31, schrieb John Pryce:
>> ...E.g., let T be infsup-binary32, and T' be infsup-binary64, and the operation be subtraction. Then suppose, in obvious notation,
>> xx_32 - yy_32 always gives zz_64.
>>
>> In fact as these are both 754-conforming types of radix 2 -- call these "nice" types -- any combination is allowed (the "typeOf" feature on the lines of "formatOf" in 754), so the current rules say there shall be an
>> xx - yy whose inputs may be any combination of nice types, giving result of type T.
>> Also
>> xx - yy whose inputs may be any combination of nice types, giving result of type T'.
>>
>> Suppose the implementation only provides the second of these. (If one wants the first, get it by taking the T-hull explicitly.) Should the standard call this non-conforming?