Universe: TT146

       Name: TT146                                                   [Show more]
       Type: Subroutine
   Category: Universe
    Summary: Print the distance to the selected system in light years
    Context: See this subroutine in context in the source code
 Variations: See code variations for this subroutine in the different versions
 References: This subroutine is called as follows:
             * TT102 calls TT146
             * TT25 calls TT146


 If it is non-zero, print the distance to the selected system in light years.
 If it is zero, just move the text cursor down a line.

 Specifically, if the distance in QQ8 is non-zero, print token 31 ("DISTANCE"),
 then a colon, then the distance to one decimal place, then token 35 ("LIGHT
 YEARS"). If the distance is zero, move the cursor down one line.


.TT146

 LDA QQ8                \ Take the two bytes of the 16-bit value in QQ8 and
 ORA QQ8+1              \ OR them together to check whether there are any
 BNE TT63               \ non-zero bits, and if so, jump to TT63 to print the
                        \ distance

 JMP INCYC              \ Move the text cursor down by one line and return from
                        \ the subroutine using a tail call

\RTS                    \ This instruction is commented out in the original
                        \ source

.TT63

 LDA #191               \ Print recursive token 31 ("DISTANCE") followed by
 JSR TT68               \ a colon

 LDX QQ8                \ Load (Y X) from QQ8, which contains the 16-bit
 LDY QQ8+1              \ distance we want to show

 SEC                    \ Set the C flag so that the call to pr5 will include a
                        \ decimal point, and display the value as (Y X) / 10

 JSR pr5                \ Print (Y X) to 5 digits, including a decimal point

 LDA #195               \ Set A to the recursive token 35 (" LIGHT YEARS") and
                        \ fall through into TT60 to print the token followed
                        \ by a paragraph break