CFLib.org – Common Function Library Project

Description:
Despite what is conventionally taught, a "5" after the digit to be rounded should not always be rounded up. Five is the exact middle of the digits that are rounded (the digit "0" is not rounded, but just truncated), and thus should only be rounded up half of the time. Non-zero digits after the five mean that it is no longer in the exact middle, so most fives do correctly round up. However, a five which is at the end of the number or which is followed by only zeros should round to the closest *even* number (and thus rounded down half of the time).

Return Values:
Returns a numeric value.

Example:

<cfoutput>
<pre>
<b>x</b>               <b>SymRound(x)</b>

(to the nearest tenth ... or 1 decimal place):
1.14            #SymRound(1.14, 1)#
1.15            #SymRound(1.15, 1)#
1.24            #SymRound(1.24, 1)#
1.25            #SymRound(1.25, 1)# *surprised?*
1.25000000000   #SymRound(1.25000000000, 1)# *surprised?*
1.25000000001   #SymRound(1.25000000001, 1)#
1.26            #SymRound(1.26, 1)#

-1.25           #SymRound(-1.25, 1)# *surprised?*
-1.251          #SymRound(-1.251, 1)#


(to the nearest hundred ... or -2 decimal places):
149             #SymRound(149, -2)#
150             #SymRound(150, -2)#
151             #SymRound(151, -2)#
249             #SymRound(249, -2)#
250             #SymRound(250, -2)# *surprised?*
251             #SymRound(251, -2)#

(to the nearest whole number):
2.5             #SymRound(2.5)# *surprised?*
</pre>
</cfoutput>

Parameters:

Full UDF Source:

/**
 * Symmetrically rounds any number to a specific decimal point, preventing a common "rounding bias" from skewing results.
 * Ver 1.1: Made numDigits an optional parameter instead of required.
 * 
 * @param theNumber      Number you want to round. (Required)
 * @param numDigits      Number of decimal places to round to.  (Optional)
 * @return Returns a numeric value. 
 * @author Shawn Seley (shawnse@aol.com) 
 * @version 1.1, October 4, 2002 
 */
function SymRound(theNumber) {
    // The decimal-place-rounding foundation of this code was based on Sierra Bufe's (sierra@brighterfusion.com) RoundIt().
    var x              = 0;
    var rounded_down   = 0;

    var numDigits      = 0;  // rounds to the nearest whole integer unless a decimal place is specified
        if(ArrayLen(Arguments) GTE 2) numDigits = Arguments[2];

    // multiply by 10 to the power of the number of digits to be preserved, and remove its sign
    x = Abs(theNumber * (10 ^ numDigits));
    rounded_down = Int(x);

    // round off to an integer, checking for the exception first
    if((x -rounded_down EQ 0.5) and (not rounded_down mod 2)) {
        // number is an exact-middle "5" AND rounding down is the closest *even* result
        x = rounded_down;
    } else x = Round(Val(x));  // otherwise round normally

    // divide by 10 to the power of the number of digits to be preserved, and restore the number's sign
    return x / (10 ^ numDigits) * Sgn(theNumber);

}