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: Gordon Woodhull (gordon_at_[hidden])
Date: 2008-12-10 18:24:01

On Dec 10, 2008, at 4:16 PM, Johan Råde wrote:

> Gordon Woodhull wrote:
>> On Dec 10, 2008, at 7:24 AM, Johan Råde wrote:
>>> Is the following true: if x and y satisfy  x <= y (or x >= y)
>>> then they will still do so after any truncation from 80 to 64 bits?
>> Nope, as John pointed out later in his message, if the test is x<=y  
>> and x is just slightly greater than y, then x can flip either way.
>
> The statement is
> "x <= y before truncation implies x <= y after truncation".
> (Note the word "implies", not "equivalent to".)
> The example you mention is not a counter-example to that statement.

Ooops, you are quite right.  In other words, perhaps truncation can  
merge two values but it can't switch them, if I understand you this  
time.

I hope this is the case.