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Bug or feature?

Slawa

 Hello

 In my script the following is used
x1=y/0.01
x1t=truncate(x1)
If x1 - an integer that x1t should be equal in a case x1 but

if y=1308.1 then
x1=130810.0
x1t=130809

Why??

Parents

  • It's not a bug. This is a normal consequence of floating point calculations in any language (C, Tcl, perl - you name it). Many things on the web about this, but this is a good reference:

    http://docs.sun.com/source/806-3568/ncg_goldberg.html

    Try doing x1-130810 and you'll see that x1 is a tiny amount below 130810 and hence when truncated it ends up as 130809. It's caused by the fact that 0.01 is an infinitely recurring sequence in binary, rather like 1/3 is 0.333 recurring in base 10 - and so if you truncate the number to a finite precision, you end up with rounding errors.

    Regards,

    Andrew.

Reply

  • It's not a bug. This is a normal consequence of floating point calculations in any language (C, Tcl, perl - you name it). Many things on the web about this, but this is a good reference:

    http://docs.sun.com/source/806-3568/ncg_goldberg.html

    Try doing x1-130810 and you'll see that x1 is a tiny amount below 130810 and hence when truncated it ends up as 130809. It's caused by the fact that 0.01 is an infinitely recurring sequence in binary, rather like 1/3 is 0.333 recurring in base 10 - and so if you truncate the number to a finite precision, you end up with rounding errors.

    Regards,

    Andrew.

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