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Asked: 2026-05-27T16:09:27+00:00

In a C++ code on linux x86_64, I need to double precision computing (+

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In a C++ code on linux x86_64, I need to double precision computing (+ or -).

26.100000000000001 – 26 + 0.10000000000000001

I got:

0.20000000000000143

I want to get 0.2.

here, the display format is not import, the computing results will be used for some if-else branch conditions. So, I only want the if-else conditions compare the 4 digits after the decimal digit.

It seems a rounding error ?

How to restrict the computing precision to 4 digits after decimal point ?

I do not want to call any functions in order to avoid overhead.

I do not want to use stringstream due to transformation overhead.

Any better ideas ?

thanks

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1 Answer

  1. Editorial Team

    The computing precision is fine. It’s the display precision you’re trying to control. You can do that with setprecision() if using <iostream> or a formatter like "%.4f" if using <stdio.h>.

    You are already calling functions since you are displaying the result as decimal!

    P.S. 0.1 cannot be exactly represented by a float, double, or any binary-mantissa format. It factors into (1/2) * (1/5), and decimal 1/5 is an infinitely-repeating digit sequence in binary.

    P.P.S. Go look at GMP. It might be your best hope.

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