float representation

Thanks Ryan!

 

Great reply! 3 more comments.

1.

"maintained internally" -- internally you mean something like Visual Studio debugger? And this is why I see 9 digits in debugger?

2.

"Two floating-point numbers that appear equal for a particular precision might not compare equal because their least significant digits are different." -- what means "least significant digits"? Could you show me a sample float-point and what parts are "least significant digits" please? From the link, I can not find the answer. :-)

3.

"A mathematical or comparison operation that uses a floating-point number might not yield the same result if a decimal number is used because the floating-point number might not exactly approximate the decimal number." -- I am totally confused.

Does it mean something like this?

float a = something;

float b = somethingelse;

float result1 = b + a;

decimal result2 = (decimal) b + (decimal) a;

result1 and result2 are different? :-)

 

regards,
George

I will give you the same response that I gave in your CodeGuru thread....

____________________________________________________________

wow....this was really hard.

straight from the MSDN

http://msdn.microsoft.com/en-us/library/system.single.aspx

"Remember that a floating-point number can only approximate a decimal number, and that the precision of a floating-point number determines how accurately that number approximates a decimal number. By default, a Single value contains only 7 decimal digits of precision, although a maximum of 9 digits is maintained internally. The precision of a floating-point number has several consequences:

• Two floating-point numbers that appear equal for a particular precision might not compare equal because their least significant digits are different.
• A mathematical or comparison operation that uses a floating-point number might not yield the same result if a decimal number is used because the floating-point number might not exactly approximate the decimal number.
• A value might not roundtrip if a floating-point number is involved. A value is said to roundtrip if an operation converts an original floating-point number to another form, an inverse operation transforms the converted form back to a floating-point number, and the final floating-point number is equal to the original floating-point number. The roundtrip might fail because one or more least significant digits are lost or changed in a conversion."

now how much longer are we going to have to spoon feed you the answers to your questions?

Just use double, it can represent just about as many as you want. Its like a "long decimal". You don't hardly see anyone using float because its restricted like that.

Thanks.

 

I understand how IEEE represents a float number. In more precise, I do not think float has enough significand to represent 9 decimal digits, it has only 7. Any ideas?

http://en.wikipedia.org/wiki/Floating_point#Implementation_in_actual_computers:_IEEE_floating-point

 

regards,

George

Didnt you ask this on CodeGuru? For shame! haha. I saw this question, and I think it was somewhat answered though... I have never used float. Just short, decimal, and double.