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Fast access to N-th figure in number

Slawa

Hello

    How quickly to receive N-th sign after a comma in number with a floating point? For example there are numbers

1.0             2.431             3.00              4.54            5.678
How to receive 3 sign after a comma for these numbers? It is necessary for me to receive in the given example of number 0 1 0 0 8 accordingly. Quantity of such primary numbers in my problem equally N therefore operation necessary for me should be the fastest.

Regards

Slawa 

Parents

  • Slawa,

    I doubt this would end up being a performance bottleneck in any practical code you write. Multiplication is pretty fast compared with many other higher level operations (such as list construction and garbage collection). You could also use something like this:

     atoi(substring(index(sprintf(nil "%.9f" n) ".") 4 1))

    I used 9 digits in the sprintf because if you only use 3, it will round the 3rd digit - depends of course what you want. I'd be really surprised if this was faster though.

    I did a quick check (using the SKILL profiler) and if I run 10 million calls to the above two different statements, the mod() version takes 15 seconds (5 of which is in gc, 4 in truncate, and only 1 in times), whereas the string-based approach takes 30 seconds, 15 of which is in sprintf, and 10 in substring and index.

    15 seconds for 10 million calls is not exactly bad... and as I said, I'd expect building a list with this number of items would almost certainly take longer.

    Regards,

    Andrew.

Reply

  • Slawa,

    I doubt this would end up being a performance bottleneck in any practical code you write. Multiplication is pretty fast compared with many other higher level operations (such as list construction and garbage collection). You could also use something like this:

     atoi(substring(index(sprintf(nil "%.9f" n) ".") 4 1))

    I used 9 digits in the sprintf because if you only use 3, it will round the 3rd digit - depends of course what you want. I'd be really surprised if this was faster though.

    I did a quick check (using the SKILL profiler) and if I run 10 million calls to the above two different statements, the mod() version takes 15 seconds (5 of which is in gc, 4 in truncate, and only 1 in times), whereas the string-based approach takes 30 seconds, 15 of which is in sprintf, and 10 in substring and index.

    15 seconds for 10 million calls is not exactly bad... and as I said, I'd expect building a list with this number of items would almost certainly take longer.

    Regards,

    Andrew.

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