approxEqual() has fooled me for a long time...

[Craig Black]

"Don" <nospam at nospam.com> wrote in message 
news:i9mhvd$2l5f$1 at digitalmars.com...
> Lars T. Kyllingstad wrote:
>> (This message was originally meant for the Phobos mailing list, but for 
>> some reason I am currently unable to send messages to it*.  Anyway, it's 
>> probably worth making others aware of this as well.)
>>
>> In my code, and in unittests in particular, I use std.math.approxEqual()
>> a lot to check the results of various computations.  If I expect my
>> result to be correct to within ten significant digits, say, I'd write
>>
>>   assert (approxEqual(result, expected, 1e-10));
>>
>> Since results often span several orders of magnitude, I usually don't
>> care about the absolute error, so I just leave it unspecified.  So far,
>> so good, right?
>>
>> NO!
>>
>> I just discovered today that the default value for approxEqual's default
>> absolute tolerance is 1e-5, and not zero as one would expect.  This
>> means that the following, quite unexpectedly, succeeds:
>>
>>   assert (approxEqual(1e-10, 1e-20, 0.1));
>>
>> This seems completely illogical to me, and I think it should be fixed
>> ASAP.  Any objections?
>
> I'm personally pretty upset about the existence of that function at all.
> My very first contribution to D was a function for floating point 
> approximate equality, which I called approxEqual.
> It gives equality in terms of number of bits. It gives correct results in 
> all the tricky special cases. Unlike a naive relative equality test 
> involving divisions, it doesn't fail for values near zero. (I _think_ 
> that's the reason why people think you need an absolute equality test as 
> well).
> And it's fast. No divisions, no poorly predictable branches.
>
> Unfortunately, somebody on the ng insisted that it should be called 
> feqrel(). Stupidly,  I listened. And now nobody uses my masterpiece 
> because it has a totally sucky name.

Where can I find this function that you wrote?  I would be interested in 
using it.

-Craig