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Herman,
This is NOT overflow !
Overflow in single precision number happens when number is greater than 3.4×1038
That is: 3800000000000000000000000000000000000000
This is the largest number that 32 bit standard IEEE can handle.
Overflow would happen when number exeeded that.
The other thing is number of *significant digits*.
This is how many digits are actually 100% accurrate - that's 7+ digits.
MUST READ:
http://en.wikipedia.org/wiki/IEEE_754
What is significant digit:
http://en.wikipedia.org/wiki/Significant_digit
Users' Guide:
http://www.amibroker.com/guide/afl/afl_view.php?almostequal
BTW: IEEE 32 bit standard is a world-wide standard for floating point arithmetic
available in ALL computer languages (in C it is represented by 'float' type).
What's more it is used in TradeStation, Wealth-Lab, Metastock and other trading apps
and you would get the same results there as well.
Best regards,
Tomasz Janeczko
amibroker.com
----- Original Message -----
From: Herman
To: Mark H
Cc: amibroker@xxxxxxxxxxxxxxx
Sent: Monday, May 14, 2007 5:47 AM
Subject: Re: [amibroker] Amibroker calculation error
You are exceeding the digit limit for AmiBroker. Do a search for "precision", its been discussed many times but I have forgotten the details.. 7 digits is the limit I seem to recall.
AmiBroker doesn't have an overflow error msg.
herman
Monday, May 14, 2007, 11:06:47 AM, you wrote:
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Herman:
My concern is not getting the date format right. There are many ways to do that.
I just need to understand why this simple calculation (add) can have error.
1070511 + 19000000 = 20070512 instead of 20070511.
My hope is that somebody (maybe TJ) can explain it to me.
This is something serious, because it affects my confidence level toward Amibroker as a whole.
Thanks,
- Mark
From: amibroker@xxxxxxxxxxxxxxx [mailto:amibroker@xxxxxxxxxxxxxxx] On Behalf Of Herman
Sent: Sunday, May 13, 2007 10:41 PM
To: Mark H
Subject: Re: [amibroker] Amibroker calculation error
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Why not use this:
Filter = 1;
SetOption("NoDefaultcolumns",False);
DateNumber = ParamDate("Date",Now(1)); // To provice test DateNum
DateString = NumToStr(DateTimeConvert( 2, DateNumber),formatDateTime);
AddTextColumn(DateString, "DateNum");
Buy = 1;
herman
Monday, May 14, 2007, 10:23:37 AM, you wrote:
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I am trying to convert a date number to a year+month+day number for better display.
It worked before, but for May 11, I got this error:
1070511 + 19000000 = 20070512 instead of 20070511.
Here is a piece of code to demonstrate this calculation error:
---------------------------------------------------------
filter = 1;
daten = StrFormat("%f", 1070511 + 19000000);
AddTextColumn(daten, "DateNum");
buy = 1;
---------------------------------------------------------
The column will display 20070512.00000, not 20070511 as you would expect.
I understand that in AFL, all numbers are in double type and integer is converted when used. However, this doesn’t seem to be a rounding error since the result is exactly 20070512.00000, not something like 20070511.71332.
I am using 4.90.5.
Have anyone seen this before?
Thanks,
- Mark
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