Format not enough precise

[Archimede]

This example
fNum := 100.22
sTest2 := Format( "{:03.15f}", fNum )
returns sTest = 100.21999999

[Xtra]

Code: Select all

fNum := 100.22
sTest2 := Format( "{:03.15f}", fNum )
MsgBox % sTest2    ; 100.220000000000000

Maybe you were mistaken you say:
returns sTest = 100.21999999
when the var name should be sTest2

Above example works fine for me.

[Archimede]

Hallo.
My last example line is not a program line, but a descriptive text, where I reported sTest instead sTest2, sorry.
The program lines are only the first 2 lines.
I controlled the value in the variable list of the developing environment.
I test it many time.
It seem me the problem is no constant: many times before it seem works well, but I found the same problem with the negative value -100.22.
It seem me that is no a constant problem.

[Tensai]

I do not believe this is a bug.
From the Docs:

https://lexikos.github.io/v2/docs/Concepts.htm#pure-numbers
Note: There are some decimal fractions which the binary floating-point format cannot precisely represent, so a number is rounded to the closest representable number. This may lead to unexpected results. For example:

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MsgBox 0.1 + 0           ; 0.10000000000000001
MsgBox 0.1 + 0.2         ; 0.30000000000000004
MsgBox 0.3 + 0           ; 0.29999999999999999
MsgBox 0.1 + 0.2 = 0.3   ; 0 (not equal)

One strategy for dealing with this is to avoid direct comparison, instead comparing the difference. For example:

Code: Select all

MsgBox Abs((0.1 + 0.2) - (0.3)) < 0.0000000000000001

Also maybe worth mentioning, I get different results from different ahk versions.
Hope this helps!

[Archimede]

Yes, thank you.
I solved the problem, but I think the problem must be solved into the language.

[lexikos]

There's nothing to "solve into the language" unless you want to wish for decimal-based floating-point numbers, instead of the binary format understood by your CPU and used by most programming languages by default.