Maths: ScaleDown (Part 2 of 4)

       Name: ScaleDown (Part 2 of 4)                                 [Show more]
       Type: Subroutine
   Category: Maths
    Summary: Balance the scale factors for the x- and y-coordinates
    Context: See this subroutine in context in the source code
 References: No direct references to this subroutine in this source file


.down6

                        \ If Y >= 0, we decrease X and Y by Y - T

 TYA                    \ If Y < 0, jump to down9 to skip the decrement loop
 BMI down9

 JMP down8              \ Y >= 0, so jump to down8 to decrement X and Y

.down7

 DEX                    \ Decrement X and Y
 DEY

.down8

 CPY T                  \ While Y >= T, loop back to decrement X and Y
 BCS down7

.down9

                        \ If X >= 0, we decrease X and Y by X - T

 TXA                    \ If X < 0, jump to down12 to skip the decrement loop
 BMI down12

 JMP down11             \ X >= 0, so jump to down11 to decrement X and Y

.down10

 DEX                    \ Decrement X and Y
 DEY

.down11

 CPX T                  \ While X >= T, loop back to decrement X and Y
 BCS down10