Overflow error

[tmighty2]

Hello!

I have the following function:

Public Function Percentage2(ByVal uMaxValue As Long, ByVal uValue As Long) As Double
On Error GoTo ErrHandler
    
    Percentage2 = (uValue * 100) / uMaxValue 

Exit Function
ErrHandler:
Debug.Print Err.Description
Debug.Assert False
End Function

If I call it with the following arguments:

       Dim i%
       i = Percentage2(867710672,  21483520)

I get the error 6 "Overflow" in this line:

       Percentage2 = (uValue * 100) / uMaxValue

At first I thought I could solve it using \ instead of /, but that wouldn't help.

Can anybody suggest how to solve this problem?

Thank you!

[OptionBase1]

Note that your function is set to return a double, and i% is an Integer, but that isn't why the overflow is happening.

21483520 * 100 = 2148352000, which exceeds the maximum value of a Long.

Try:

Percentage2 = (uValue / uMaxValue) * 100

[tmighty2]

Thank you!

[Elroy]

Hi tmighty2,

VB6 has the nice Decimal type that can be used for these very large integers. You can only get to them through the use of a Variant, and you can only assign to them using the CDec() function. But, once you've got your variables (Decimals in Variants), you can do all the typical math with them, and they'll stay Decimals, not overflowing until you hit MUCH larger numbers than yours. They're effectively a 12 byte unsigned integer with a separate sign bit.

Here are some of the usage rules for them:

    ' +, -, *, /    Decimal is at the top of the hierarchy.
    '               The hierarchy is: Byte, Integer, Long, Single, Double, Currency, Decimal.
    ' \, Mod        Results is Long, not Decimal.
    ' ^             Results is Double, not Decimal.
    ' Int()         Works on Decimals.
    ' Fix()         Works on Decimals.
    ' Abs()         Works on Decimals.
    ' Sgn()         Works on Decimals, although result is an Integer.
    ' Sqr(), etc.   Most of these functions (including trig) return Double, not Decimal.
    ' AND,OR,etc.   These convert to Long, which may cause overflow.
    '
    ' Largest Decimal:      +/- 79228162514264337593543950335.  2^96-1 (sign bit handled separately)
    ' Smallest Decimal:     +/- 0.0000000000000000000000000001  Notice that both largest and smallest are same width.

Good Luck,
Elroy