How can i get the correct decimal value without truncation ?
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Hi! I m working on a c++ project in which I have two values one is 987654321123456789 and another is 1000000000000000000. My problem is that I m dividing first value by second value which is a decimal type value in result, when I do this I store the result in a double value after typecasting the above calculation by double but it give wrong result. The result is .98755432112346 which is wrong the exact result is .987554321123456789. The code which I use is as -. double dd = double(987554321123456789 /1000000000000000000) After calculation dd = .98755432112346 which is wrong because the actual result is .987554321123456789. So how I do this calculation so that I get the correct result please help me regarding this Thanks
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Hi! I m working on a c++ project in which I have two values one is 987654321123456789 and another is 1000000000000000000. My problem is that I m dividing first value by second value which is a decimal type value in result, when I do this I store the result in a double value after typecasting the above calculation by double but it give wrong result. The result is .98755432112346 which is wrong the exact result is .987554321123456789. The code which I use is as -. double dd = double(987554321123456789 /1000000000000000000) After calculation dd = .98755432112346 which is wrong because the actual result is .987554321123456789. So how I do this calculation so that I get the correct result please help me regarding this Thanks
nitin_pro wrote:
So how I do this calculation so that I get the correct result please help me regarding this
You can't. Approximation it's the very nature of floating point numbers (possibly because memory locations can hold only a discrete set of values). See [^]. :)
If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke -
Hi! I m working on a c++ project in which I have two values one is 987654321123456789 and another is 1000000000000000000. My problem is that I m dividing first value by second value which is a decimal type value in result, when I do this I store the result in a double value after typecasting the above calculation by double but it give wrong result. The result is .98755432112346 which is wrong the exact result is .987554321123456789. The code which I use is as -. double dd = double(987554321123456789 /1000000000000000000) After calculation dd = .98755432112346 which is wrong because the actual result is .987554321123456789. So how I do this calculation so that I get the correct result please help me regarding this Thanks
The FPU (x87) uses 80-bit fields for its operations for loading and storing back and forth from the x87 stack. However the Microsoft run-time library sets the default internal precision of the math coprocessor to 64 bits in Windows XP. This can be controlled by the function _controlfp which is documented here: http://msdn2.microsoft.com/en-us/library/e9b52ceh(VS.80).aspx[^] There are some documents where Microsoft claims the precision can be changed to the full 80 bits such as this document: http://support.microsoft.com/kb/q263213/[^] These documents conflict with some of the statements in this document: http://msdn2.microsoft.com/en-us/library/y0ybw9fy(VS.80).aspx[^] Such things are common in the MSDN. I personally believe its a documentation error or perhaps they are not explaining all of the details. I have never tried it nor tested it however. Try it and see. Best Wishes, -David Delaune
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Hi! I m working on a c++ project in which I have two values one is 987654321123456789 and another is 1000000000000000000. My problem is that I m dividing first value by second value which is a decimal type value in result, when I do this I store the result in a double value after typecasting the above calculation by double but it give wrong result. The result is .98755432112346 which is wrong the exact result is .987554321123456789. The code which I use is as -. double dd = double(987554321123456789 /1000000000000000000) After calculation dd = .98755432112346 which is wrong because the actual result is .987554321123456789. So how I do this calculation so that I get the correct result please help me regarding this Thanks
i forgot to mention the /Op compiler switch for older compilers which also modifies FPU results. It is documented here: http://msdn2.microsoft.com/en-us/library/aa278532(VS.60).aspx[^] I believe in modern compilers VS 8.0 and above that this was superceeded by the switch /fp to set floating point behavior. It is documented here: http://msdn2.microsoft.com/en-us/library/e7s85ffb.aspx[^] Best Wishes, -David Delaune
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Hi! I m working on a c++ project in which I have two values one is 987654321123456789 and another is 1000000000000000000. My problem is that I m dividing first value by second value which is a decimal type value in result, when I do this I store the result in a double value after typecasting the above calculation by double but it give wrong result. The result is .98755432112346 which is wrong the exact result is .987554321123456789. The code which I use is as -. double dd = double(987554321123456789 /1000000000000000000) After calculation dd = .98755432112346 which is wrong because the actual result is .987554321123456789. So how I do this calculation so that I get the correct result please help me regarding this Thanks
And another link for you... :) [29.16] Why is floating point so inaccurate?[^]
--Mike-- Visual C++ MVP :cool: LINKS~! CP SearchBar v3.0 | C++ Forum FAQ Dunder-Mifflin, this is Pam.
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nitin_pro wrote:
So how I do this calculation so that I get the correct result please help me regarding this
You can't. Approximation it's the very nature of floating point numbers (possibly because memory locations can hold only a discrete set of values). See [^]. :)
If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain ClarkeHi! Actually my problem is that when I perform double dd = double(987554321123456789 /1000000000000000000) this calculation the result is truncated up to 15 digit and it gives result dd = 0.98755432112346 but I want result completely means up to 18 digit may be it’s the limitation of Double data type that it can only store result up to 15 digit bt if it is tn I need some other data type which can store complete result yp to 18 digit. Pls help me to store complete result manse 0.987554321123456789 without truncation .
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Hi! Actually my problem is that when I perform double dd = double(987554321123456789 /1000000000000000000) this calculation the result is truncated up to 15 digit and it gives result dd = 0.98755432112346 but I want result completely means up to 18 digit may be it’s the limitation of Double data type that it can only store result up to 15 digit bt if it is tn I need some other data type which can store complete result yp to 18 digit. Pls help me to store complete result manse 0.987554321123456789 without truncation .
Why don't you keep it inside
long longassuming implicit multiplication by10^18?If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
