Longs and bitwise stuff.

I've got an array of Longs with a typical value of $20FFFFFF00004000. I want to be able to change the first byte (the $20) to any arbitrary value, leaving all other bits unchanged.

I'm having a late-night brain fart and cannot think how to do it. I'm going to bed now because I'm obviously dumb and tired :)

If anyone can point out a way of achieving this simple task, I would be eternally grateful :D

edited as it was wrong

Or'ing will combine with existing data in that byte. If there's a previous value there it will turn into something unwanted.

Also shifting left 64 bits shifts the value entirely out of the range of the long, into a 9th byte.

You also need to do an AND first to `clear` the byte.

value:& $00FFFFFFFFFFFFFF
value:| (secondvalue shl 56)

Note that secondvalue, as a variable, should be a Long variable, or it will become empty when shifting past bit 31. Or, you can cast it as a Long:

value:| (Long(secondvalue) Shl 56)