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Comment by lifthrasiir

1 day ago

Your problem is practically important as it can be considered as the "canonical" string representation of given floating point number (after adding the closestness requirement). There are many efficient algorithms as a result, selected algorithms include Dragon4, Grisu3, Ryu and Dragonbox. See also Google's double-conversion library which implements first two of them.

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lifthrasiir

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jjcob  1 day ago

Thank you for pointing me to all the prior work on this!

I am surprised how complex the issue seems to be. I assumed there might be an elegant solution, but the problem seems to be a lot harder than I thought.

  • pklausler  15 hours ago

    See also the code in LLVM Flang for binary/decimal conversions. Minimal-digit decimals don’t come up in Fortran as often as other languages, but I use them when allowed by the output format. Interestingly, the last digit of a minimal decimal conversion is often irrelevant, so long as it exists.

unnah  1 day ago

Since such algorithms were developed in the 1990's, nowadays you can expect your language's standard library to use them for float-to-decimal and decimal-to-float conversions. So all you need to do in code is to print the float without any special formatting instructions, and you'll get the shortest unique decimal representation.

  • lifthrasiir  1 day ago

    Except that C specifies that floating point numbers should be printed in a fixed precision (6 decimal digits) when no precision is given. Internally they do use some sort of float-to-decimal algorithms [1], but you can't get the shortest representation out of them.

    [1] Some (e.g. Windows CRT) do use the shortest representation as a basis, in which case you can actually extract it with large enough precision (where all subsequent digits will be zeros). But many libcs print the exact representation instead (e.g. 3.140000000000000124344978758017532527446746826171875 for `printf("%.51f", 3.14)`), so they are useless for our purpose.