# Re: Sorting numeric strings

From:
Gene Wirchenko <genew@ocis.net>
Newsgroups:
comp.lang.java.programmer
Date:
Wed, 02 May 2012 19:57:37 -0700
Message-ID:
<9rr3q7t3jnl80m5jhk4vaplvs5c85jh5sh@4ax.com>
On Wed, 02 May 2012 14:36:29 -0700, Roedy Green
<see_website@mindprod.com.invalid> wrote:

On Tue, 01 May 2012 15:02:09 -0700, Patricia Shanahan <pats@acm.org>
wrote, quoted or indirectly quoted someone who said :

Whether comparing doubles gives the correct result does depend on the
maximum number of significant digits. BigDecimal is always safe for
this, no matter how many significant digits.

A float will do for about 7 significant digits. A double will do for
16.

A currency amount can be shown with a double to the penny up to 99
trillion dollars
99,000,000,000,000.00,

If you are thinking of IEEE 754 64-bit floating point, well, it
has ~15.95 decimal digits of precision so it is not quite good enough
for 16 digits. 15 digits is fine though. (The 32-bit vesion is good
for ~7.22 digits.)

Here is a counterexample in JavaScript. Adding 8765432101234567
and 1234567890123456 gives 9999999991358024 which is one too high. I
get the same result in Java (except that it is in E-notation) with:

***** Start of Code *****
class tmp
{

public static void main(String [] args)
{
double a=8765432101234567d;
double b=1234567890123456d;

System.out.println(a);
System.out.println(b);
System.out.println(a+b);
}

}
***** End of Code *****

I researched in this area when I was figuring out how to handle
fixed-point numbers using JavaScript's number object which uses IEEE
754 64-bit floating point.

Sincerely,

Gene Wirchenko

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