On Mar 1, 2010, at 2:32 PM, ik wrote:
http://ik.homelinux.org/
On Mon, Mar 1, 2010 at 23:20, Jerry <lancebo...@qwest.net> wrote:
Don't compare floating points. Ever. Now you see why.
So if I need for example to compare currency or something that is
floating point, how do I do that ?
Also, don't write loops that calculate a floating point number which
is then tested for equality to exit the loop. Also, it is a bad idea
to test for > or < for exiting unless you know in advance an
accidental equality result will not yield surprising results. In
other other words, don't do that (test for > or <) either.
As I understand, there is an old way to calculate floating point
that is very popular and newer ways for that.
The old way uses binary calculation and the newer I do not
understand them :)
The older way that you are thinking of might be binary coded decimal,
BCD, in which each decimal digit is represented by its own bit string,
usually four bits, to represent the digits 0–9. It is rarely used any
more. I'm not sure but maybe Hewlett-Packard calculators use BCD. (HP
calculators are known for their excellent numerical accuracy. The
academic who did a lot of their work was also involved in the IEEE 754
standard, I think.)
The newer way that you are thinking of is probably IEEE 754 floating
point which is implemented widely on modern microprocessors. Its whole
numbers (1.0, 2.0, etc.) are supposedly exact equivalents to integer
counterparts up to a very large number, but you had _really_ better
know what you are doing if you depend on that for comparisons. And
expect portability problems when moving to non-IEEE 754 platforms.
BTW, the way to write a loop that increments a floating point number
properly is this (Please pardon if any Ada syntax slips in here):
for i := 0 .. 100 begin
a_float := 1.23 * i;
end;
whereas this is a bad idea:
a := 0.0;
while a <= 100.0 do
a_float := 1.23 * i;
a := a + 1.0;
end;
as is this:
a := 0.0;
while a <= 123.0 do
a := a + 1.23;
end;
Jerry
Jerry
On Feb 26, 2010, at 3:37 AM, ik wrote:
Hello,
I've made a small test:
if (0.1+0.2) = 0.3 then
The only compiler/interpator that actually tells that it equal is
FPC.
I've tested it using Javascript (in Firefox), Ruby, Python, C (gcc)
and Perl.
Except FPC, everyone tells that 0.1+0.2 = 0.30000000000000004
Can someone explain how FPC see the result and why others does not
see it like that ?
Thanks,
Ido
http://ik.homelinux.org/
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Ido
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