Significant Digits (Significant Figures)

Discussion in 'Javascript' started by SMH, Jan 7, 2007.

  1. SMH

    SMH Guest

    Anyone found any mature/well-tested code that actually produces
    significant figures for any real number result of an arithmetic operation,
    of course represented as a string.

    This is code I developed some time ago, but I don't think all the bugs
    have been worked out or that all the logic is sound, given the criteria
    for determining significant digits.

    ======= begin code ========

    /* Two functions are defined:

    1. getSigDigits() is supposed to return to the caller the
    count of significant digits of the argument passed to it.

    The function takes a single argument of type string or number.
    If passed a string, it uses regular expressions to attempt
    to find the count of signficant digits.
    If passed a number, it renders the number to a string
    represented by the toExponential() method and then uses
    a regular expression to attempt to analyze the mantissa.

    2. setSigDigits() is supposed to return to the caller a number
    properly formatted (and rounded) represented as a string
    with the proper significant digits.

    It takes two arguments:
    (i) parameter #1 is the value to be adjusted/formatted, and
    can be of type string or number (limited argument checking
    is done; and could probaby be improved)
    (ii) parameter #2 is the count of significant digits to use
    to format the value; more extensive argument checking is
    done to make sure it is a positive integer, and a default
    is applied if there is a range or type error.

    The function essentially attempts to obtain a mantissa
    of a number that might be expressed in scientific notation,
    to which rounding is applied in the case of truncation or
    to which the number is extended with zeroes.

    The idea would be to determine the count of significant
    digits on each operand in an arithmetic operation using
    getSigDigits(), producing the answer/result, and then
    formatting the answer with setSigDigits().

    */


    function getSigDigits(value)
    {
    var result;
    if (typeof(value) == "string")
    {
    var sigdigs = 0;
    result = value.match(/(\d+)\.?(\d*)|(\d*)\.?(\d+)/);
    if (result[1] != null || results[2] != null)
    {
    sigdigs += results[1] ? result[1].length : 0;
    sigdigs += results[2] ? result[2].length : 0;
    return (sigdigs);
    }
    sigdigs += results[3] ? result[3].length : 0;
    sigdigs += results[4] ? result[4].length : 0;
    return (sigdigs);
    }
    else if (typeof(value) != "number")
    return (null);
    if ((result = value.toExponential().match
    (/[eE]{1}[+\-]?\d{1,3}/)) == null)
    return (null);
    return (result[1].length);
    }

    function setSigDigits(value, digits)
    {
    if (typeof(value) == "undefined" || value == null)
    return (null);
    var exp, val;
    if (isNaN(digits) == true || digits <= 0)
    digits = 6;
    var sign = 1;
    if (value != 0.0)
    {
    var sign = 1;
    if (value < 0)
    {
    sign = -1;
    value = Math.abs(value);
    }
    val = log10(value);
    val -= (exp = Math.floor(val)) - 7;
    val = Math.round(Math.pow(10, val));
    val = Math.pow(10, log10(val) - 7 + exp);
    val *= sign;
    }
    else
    val = value;
    val = new String(val);
    if (val.search(/\./) > digits)
    val = val.substr(0, digits);
    else
    val = val.substr(0, digits + 1);
    return (val);
    }


    ======= end code ========
    SMH, Jan 7, 2007
    #1
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