This is all very debatable, some may find this easy to read others like me,
go completely banana's scrolling from the code portion to the equates
portion. for me it would be easiest to have

GP4    equ   1<<4
GP5    equ   1<<5
....
movlw  GP4 | GP5                ; mask

OR

movlw   b'00110000'             ; mask: GP4 | GP5

which would require no scrolling and be perfectly clear.

Peter van Hoof
-------------
>
> You'd probably be better off reading the MPASM documentation on the 'equ'
> directive. But I'll give a very brief summary.
>
> First, GP4 and GP5 have to be defined because the assembler has no idea
> what they are. Most constants are defined with the equ (short for equate)
> directive. So I'd probably define GP4 and GP5 like this:
>
> GP4    equ   1<<4
> GP5    equ   1<<5
>
> This associates the value 1<<4 or 0x10 with the label GP4 and 1<<5 or 0x20
> with the label GP5. Once this is done, you can use the constants GP4 and
> GP5 and the assembler will replace them with thier equivalent numerical
> values.
>
> So,
>
> MASK   equ   GP4 | GP5
>
> will assign the logical OR (that's what the '|' means) of GP4 and GP5 to
> MASK. Since GP4 and GP5 are equal to 0x10 and 0x20, MASK will become 0x10
> | 0x20 which is 0x30. Is that clear?
>
> Now you could've just said:
>
> MASK  equ 0x30
>
> or simpler yet:
>
>    movlw  0x30
> instead of
>    movlw  MASK
>
> and everything would've worked just fine. However, 6 months down the road
> when you have to go and fix a bug in this code you're going to need every
> bit of help you can get. These symbols will make the code more readable
> and comprehensible. It doesn't slow the execution down at all. So use them
> where ever possible!