Re: [boost] [review][constrained_value] Review of Constrained Value Library begins today

Subject: Re: [boost] [review][constrained_value] Review of Constrained Value Library begins today
From: Thorsten Ottosen (nesotto_at_[hidden])
Date: 2008-12-11 04:31:22

Johan RÃ¥de skrev:
> Robert Kawulak wrote:
>>> From: Johan Rade
>>> The statement is
>>> "x <= y before truncation implies x <= y after truncation".
>>
>> Or more specifically:
>> "x < y before truncation implies x <= y after truncation"
>> Is this right?
>>
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> 
> Thought about it again.
> None if these statements are true, unfortunately,
> if you consider the case when one number is truncated to 64 bits
> and the other is kept at 80 bits.
> Then you can even have x < y before and x > y after.

Hm. This sucks.

Do we know if that 80-bit floating point values are guaranteed to be a 
superset of 64-bit and 32-bit floats (or if 64-bit is a superset of 
32-bit floats).

I suspect the answer might be yes. If so, I don't think

   x < y before ==> x > y after

can be true. If x is rounded upwards, y would be an upper bound.

-Thorsten