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⌂ ∞ Elite on the BBC Micro and NES

Maths (Arithmetic): GC2

[BBC Micro disc version, Flight]

       Name: GC2                                                     [Show more]
       Type: Subroutine
   Category: Maths (Arithmetic)
    Summary: Calculate (Y X) = (A P) * 4

    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * TT151 calls GC2




 Calculate the following multiplication of unsigned 16-bit numbers:

   (Y X) = (A P) * 4



.GC2

 ASL P                  \ Set (A P) = (A P) * 4
 ROL A
 ASL P
 ROL A

 TAY                    \ Set (Y X) = (A P)
 LDX P

 RTS                    \ Return from the subroutine