Maths (Arithmetic): GetNextSeed0To22

       Name: GetNextSeed0To22                                        [Show more]
       Type: Subroutine
   Category: Maths (Arithmetic)
    Summary: Set A to the next number from the landscape's sequence of seed
             numbers, converted to the range 0 to 22
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * GenerateLandscape calls GetNextSeed0To22
             * SpawnTrees calls GetNextSeed0To22


.GetNextSeed0To22

 JSR GetNextSeedNumber  \ Set A to the next number from the landscape's sequence
                        \ of seed numbers

 PHA                    \ Set T to bits 0-2 of A
 AND #%00000111         \
 STA T                  \ So T is a number in the range 0 to 7
 PLA

 LSR A                  \ Set A to bits 3-6 of A and clear the C flag
 LSR A                  \
 AND #%00011110         \ So T is a number in the range 0 to 15
 LSR A

 ADC T                  \ Set A = A + T
                        \
                        \ So A is a number in the range 0 to 22

 RTS                    \ Return from the subroutine