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Re: Gradual-Underflow Wars

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On 05/07/2011 04:50 AM, Lawrence D'Oliveiro wrote:
> Nowadays we take IEEE-754 arithmetic for granted (at least in the hardware;
> language support is another matter, unless you’re using an enlightened
> language like GCC or Python). It was a different matter in the late 1970s,
> when the idea for a standard floating-point architecture first came
> together, spurred by Intel’s development of its 8087 chip.
>
> Hard to believe it now, but the most controversial aspect of the proposal
> was its support for denormalized numbers, to fill in the underflow gap
> between the closest normalized number to zero, and zero itself. In theory
> you could write code that would work correctly without such help, but most
> people didn’t have that kind of skill in numerics. And still don’t.
>
> <http://www.eecs.berkeley.edu/~wkahan/ieee754status/754story.html>
>
> Kahan also has a paper elsewhere deriding the floating-point limitations of
> Java. Java does not distinguish between NaN and infinity, and provides no

Bullshit.  Ignorant bullshit.

<http://download.oracle.com/javase/6/docs/api/java/lang/Double.html#NaN>
<http://download.oracle.com/javase/6/docs/api/java/lang/Double.html#NEGATIVE_INFINITY>
<http://download.oracle.com/javase/6/docs/api/java/lang/Double.html#POSITIVE_INFINITY>

Stop lying.

> way of querying and controlling floating-point exceptions (in the IEEE-754
> sense of “exception”).
>
> His paper was published in 1998, and is still a valid criticism today.

 From the JLS, §4.2.4:
"Operators on floating-point numbers behave as specified by IEEE 754 (with the 
exception of the remainder operator (§15.17.3)). In particular, the Java 
programming language requires support of IEEE 754 denormalized floating-point 
numbers and gradual underflow, ...

"An operation that overflows produces a signed infinity, an operation that 
underflows produces a denormalized value or a signed zero, and an operation 
that has no mathematically definite result produces NaN."

So much for "does not distinguish".

-- 
Lew
Honi soit qui mal y pense.
http://upload.wikimedia.org/wikipedia/commons/c/cf/Friz.jpg

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Gradual-Underflow Wars Lawrence D'Oliveiro <ldo@geek-central.gen.new_zealand> - 2011-05-07 20:50 +1200
  Re: Gradual-Underflow Wars Lew <noone@lewscanon.com> - 2011-05-07 08:06 -0400

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