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  4. Elliminate the e symbol from doubles

Elliminate the e symbol from doubles

Scheduled Pinned Locked Moved C / C++ / MFC
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  • C CPallini

    Blood_HaZaRd wrote:

    x= 1.123456789 e09

    Blood_HaZaRd wrote:

    x = 1123456789

    Since they are different representations of the same number, both of them are stored, in a double, with the same bit pattern. :)

    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
    [My articles]

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    Schehaider_Aymen
    wrote on last edited by
    #7

    it's clear that they have the same number but God its seems that the fmod doesn't make a correct modulo with double or i missed sth else with that fucntion ...

    //i have x = 105145010021234567890311169400 which is also equal to 1.0514501002123e+029
    double alpha = fmod (x, 97) //alpha will be equal to 16.000000000000

    or with calculator x modulo 97 = 92 it sounds my computer is hollowed :doh:

    "The Ultimate Limit Is Only Your Imagination."

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    • S Schehaider_Aymen

      ok o how could u explain this : i have double x = 105145010021234567890311169400. and when i make double y = fmod(x, 97) it gives me 16 or when i calculte it with a calculator it gives me 92

      "The Ultimate Limit Is Only Your Imagination."

      N Offline
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      Niklas L
      wrote on last edited by
      #8

      Your value cannot be stored within a double precision floating point number (64 bit IEEE whatever) It simply holds too much information, so your system will have to round it off.

      home

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      • S Schehaider_Aymen

        ok o how could u explain this : i have double x = 105145010021234567890311169400. and when i make double y = fmod(x, 97) it gives me 16 or when i calculte it with a calculator it gives me 92

        "The Ultimate Limit Is Only Your Imagination."

        N Offline
        N Offline
        Niklas L
        wrote on last edited by
        #9

        Read about Floating point numbers[^]

        home

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        • S Schehaider_Aymen

          ok o how could u explain this : i have double x = 105145010021234567890311169400. and when i make double y = fmod(x, 97) it gives me 16 or when i calculte it with a calculator it gives me 92

          "The Ultimate Limit Is Only Your Imagination."

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          Aescleal
          wrote on last edited by
          #10

          You'll never get a representation of that integer into a double without loosing a chunk of accuracy. 105145010021234567890311169400 is 0xE97804B9A34AB4E which is going to take about 60 bits to hold. As a double only has 53 bits to store digits you've already rounded your number to the nearest multiple of 128 by storing it in a double. So as it's an integer, store it in an integer - the e bit is non-negotiable with a floating point number and has no bearing at all on your problem. Ash

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          • A Aescleal

            You'll never get a representation of that integer into a double without loosing a chunk of accuracy. 105145010021234567890311169400 is 0xE97804B9A34AB4E which is going to take about 60 bits to hold. As a double only has 53 bits to store digits you've already rounded your number to the nearest multiple of 128 by storing it in a double. So as it's an integer, store it in an integer - the e bit is non-negotiable with a floating point number and has no bearing at all on your problem. Ash

            S Offline
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            Schehaider_Aymen
            wrote on last edited by
            #11

            ok so the best solution is to navigate into mthemticl splitting and mke the purpose by slices

            "The Ultimate Limit Is Only Your Imagination."

            N 1 Reply Last reply
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            • S Schehaider_Aymen

              it's clear that they have the same number but God its seems that the fmod doesn't make a correct modulo with double or i missed sth else with that fucntion ...

              //i have x = 105145010021234567890311169400 which is also equal to 1.0514501002123e+029
              double alpha = fmod (x, 97) //alpha will be equal to 16.000000000000

              or with calculator x modulo 97 = 92 it sounds my computer is hollowed :doh:

              "The Ultimate Limit Is Only Your Imagination."

              C Offline
              C Offline
              CPallini
              wrote on last edited by
              #12

              Blood_HaZaRd wrote:

              //i have x = 105145010021234567890311169400 which is also equal to 1.0514501002123e+029

              That is wrong. As I stated before, double cannot represent such big integer numbers with the required (by you) accuracy:

              1.0514501002123e+029 = 105145010021230000000000000000

              i.e. there's a big difference with 105145010021234567890311169400. Bottom line: you cannot use a double for the intended purpose (after all, doubles are 64 bit numbers: they would have 'mystical powers' in order to represent an integer better than a 64 bit int itself). :)

              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
              [My articles]

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              • C CPallini

                Blood_HaZaRd wrote:

                //i have x = 105145010021234567890311169400 which is also equal to 1.0514501002123e+029

                That is wrong. As I stated before, double cannot represent such big integer numbers with the required (by you) accuracy:

                1.0514501002123e+029 = 105145010021230000000000000000

                i.e. there's a big difference with 105145010021234567890311169400. Bottom line: you cannot use a double for the intended purpose (after all, doubles are 64 bit numbers: they would have 'mystical powers' in order to represent an integer better than a 64 bit int itself). :)

                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
                [My articles]

                S Offline
                S Offline
                Schehaider_Aymen
                wrote on last edited by
                #13

                May i use a 128 bit integer or double nd if yes how to do that so

                "The Ultimate Limit Is Only Your Imagination."

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                • S Schehaider_Aymen

                  May i use a 128 bit integer or double nd if yes how to do that so

                  "The Ultimate Limit Is Only Your Imagination."

                  C Offline
                  C Offline
                  CPallini
                  wrote on last edited by
                  #14

                  Yes, if you have them. :)

                  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
                  [My articles]

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                  • S Schehaider_Aymen

                    ok so the best solution is to navigate into mthemticl splitting and mke the purpose by slices

                    "The Ultimate Limit Is Only Your Imagination."

                    N Offline
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                    norish
                    wrote on last edited by
                    #15

                    One solution is using Multiple Precision Number library like http://gmplib.org/[^]

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                    • N norish

                      One solution is using Multiple Precision Number library like http://gmplib.org/[^]

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                      Schehaider_Aymen
                      wrote on last edited by
                      #16

                      i alredy downloaded the GMP zip files but i had problems to use it in MVS 6.0 .. i m a newbie in such manipulations (integrating foreign files inti my project) . may be when my skills will be better i 'll try it :laugh:

                      "The Ultimate Limit Is Only Your Imagination."

                      L 1 Reply Last reply
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                      • S Schehaider_Aymen

                        i alredy downloaded the GMP zip files but i had problems to use it in MVS 6.0 .. i m a newbie in such manipulations (integrating foreign files inti my project) . may be when my skills will be better i 'll try it :laugh:

                        "The Ultimate Limit Is Only Your Imagination."

                        L Offline
                        L Offline
                        Lost User
                        wrote on last edited by
                        #17

                        I think you need to spend some more time reading about floating point number representations. A floating point (double) number allows you to store extremely large or extremely small values and anything in between, but at a cost of accuracy in these values. Thus they are no good for applications where numeric accuracy is important, e.g. anything to do with money. When you display such numbers on screen or printer you have various options for how you wish them to be represented on screen: in scientific 1.3456e-2, or decimal 0.013456 etc. If you want to use very large numbers with no loss of accuracy then you need to find a library or class (or write one) that can do it for you.

                        It's time for a new signature.

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