8-bit values may be concatenated to get larger numbers or truncated to get
smaller numbers.
For example, if you have 0-255 this is 0 to 0xFF or 00000000 to 11111111 in
binary.
If you want the 0-31, you can simply AND with 0x1F to get the required
range:
in C this is
outValue = inValue & 0x1F;
If you want a larger power of 2 then you just concatenate to the required
number of bits and AND with the number of bits you want to have,
For 4194303 (2^22-1) in C this is:
outValue = ((inValue1 << 16) | (inValue2 <<8) | inValue3) & 0x3FFFFF;
The simplest way to get another integer range is to concatenate the number
of bits required to get a higher number that you want then discard all
values above it (this is ok, since every value is equally probable).
For 2456743 in C this can be done like this:
tempValue = ((inValue1 << 16) | (inValue2 <<8) | inValue3) & 0x3FFFFF;
/* Gives a value between 0 and 4194303 */
if(tempValue <= 2456743) /* only use if <= the required range */
{
outValue=tempValue;
}
There are more efficient methods of doing this but are dependent on the
application (Google will help you with this).
.
