Calculating the maximum value for a decimal using scale and precision

I am working on a JavaScript function that takes two values: precision of a decimal value & scale of a decimal value.

This function should calculate the maximum value that can be stored in a decimal of that size.

For example: a decimal with a precision of 5 and a scale of 3 would have a maximum value of 99.999.

What I have does the job, but it’s not elegant. Can anyone think of something more clever?

Also, please forgive the use of this weird version of Hungarian notation.

function maxDecimalValue(pintPrecision, pintScale) {
    /* the maximum integers for a decimal is equal to the precision - the scale.
        The maximum number of decimal places is equal to the scale.
        For example, a decimal(5,3) would have a max value of 99.999
    */
    // There's got to be a more elegant way to do this...
    var intMaxInts = (pintPrecision- pintScale);
    var intMaxDecs = pintScale;

    var intCount;
    var strMaxValue = "";

    // build the max number.  Start with the integers.
    if (intMaxInts == 0) strMaxValue = "0";    
    for (intCount = 1; intCount <= intMaxInts; intCount++) {
        strMaxValue += "9";
    }

    // add the values in the decimal place
    if (intMaxDecs > 0) {
        strMaxValue += ".";
        for (intCount = 1; intCount <= intMaxDecs; intCount++) {
            strMaxValue += "9";
        }
    }
    return parseFloat(strMaxValue);
}

Answer

Haven’t tested it:

function maxDecimalValue(precision, scale) {
    return Math.pow(10,precision-scale) - Math.pow(10,-scale);
}

precision must be positive

maxDecimalValue(5,3) = 10^(5-3) - 10^-3 = 100 - 1/1000 = 99.999
maxDecimalValue(1,0) = 10^1 - 10^0 = 10 - 1 = 9
maxDecimalValue(1,-1) = 10^(1+1) - 10^1 = 100 - 10 = 90
maxDecimalValue(2,-3) = 10^(2+3) - 10^3 = 100000 - 1000 = 99000

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Answer