PRB: JScript returns overflow error on numbers like 0xFFnnnnnn

Description

Sometimes when working in JScript, you can face the challenge: assigning such numbers as 0xFFnnnnnn (for example color properties of Graphics Processor, which you must set in ARGB format; first two digits are often FF to describe opaque color) causes overflow error. For example the following code will cause this error:



Reason

The problem is that JScript assumes that oDrawingTool.DefaultPen.Color has type signed long (which cannot be larger than 0x7FFFFFFF) and numbers which are larger than 0x7FFFFFFF has type unsigned long.

Solution

Unfortunately JScript does not provide standard ways to cast from unsigned to signed types. However there some workarounds:

1. You can use negative numbers. For example 0xFFFFFFFF is the same as -1. However it is very inconvenient.

2. Applying bitwise operations can help. When we use some bitwise operation and one of operands is signed, another is unsigned, the result is signed. So to get 0xFF0000FF we can use the following operation: (0x0F0000FF | 0xF0000000). The code will be the following:



3. Don't use such numbers. Sometimes we can use constants. For example Graphics Processor contains a lot of color constants which are more readable and convenient to use. Here is a code sample how to use Graphics Processor constants:

Edited by user Wednesday, October 29, 2008 2:14:55 PM(UTC)  | Reason: Not specified