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Adding Floating-Point Decimals for Fun and Profit

62 points · 35 comments · ibobev

  1. amelius · · focus · HN ↗
    > Many people know that you shouldn’t do decimal calculations, such as those involving U.S. dollars and cents, with the floating-point numbers in most programming languages. This is because decimal numbers can’t be expressed exactly as such floating-point numbers, so you will encounter rounding errors.

    Why not, rounding to the nearest cent is going to be much less precise for any realistic amount of dollars when using 64 bit floats (the type of float Javascript uses in every browser).

    1. glimshe · · focus · HN ↗
      The rounding behavior with true decimals is easy to control and understand across number magnitudes and doesn't suffer from platform specific quirks like floats/doubles.

      The article's images clearly show the rounding error mess your get without decimals.

      1. sobriquet9 · · focus · HN ↗
        There's still catastrophic cancellation, where subtracting two large numbers that are very close results in an answer with reduced precision.
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