Maths (Geometry): FAROF

       Name: FAROF                                                   [Show more]
       Type: Subroutine
   Category: Maths (Geometry)
    Summary: Compare x_hi, y_hi and z_hi with 224
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * Main flight loop (Part 12 of 16) calls FAROF


 Compare x_hi, y_hi and z_hi with 224, and set the C flag if all three <= 224,
 otherwise clear the C flag.

 This routine does a similar job to the routine of the same name in the BBC
 Master version of Elite, but the code is significantly different.


 Returns:

   C flag               Set if x_hi <= 224 and y_hi <= 224 and z_hi <= 224

                        Clear otherwise (i.e. if any one of them are bigger than
                        224)


.FAROF

 LDA INWK+2             ; If any of x_sign, y_sign or z_sign are non-zero
 ORA INWK+5             ; (ignoring the sign in bit 7), then jump to faro2 to
 ORA INWK+8             ; return the C flag clear, to indicate that one of x, y
 ASL A                  ; and z is greater than 224
 BNE faro2

 LDA #224               ; If x_hi > 224, jump to faro1 to return the C flag
 CMP INWK+1             ; clear
 BCC faro1

 CMP INWK+4             ; If y_hi > 224, jump to faro1 to return the C flag
 BCC faro1              ; clear

 CMP INWK+7             ; If z_hi > 224, clear the C flag, otherwise set it

.faro1

                        ; By this point the C flag is clear if any of x_hi, y_hi
                        ; or z_hi are greater than 224, otherwise all three are
                        ; less than or equal to 224 and the C flag is set

 RTS                    ; Return from the subroutine

.faro2

 CLC                    ; Clear the C flag to indicate that at least one of the
                        ; axes is greater than 224

 RTS                    ; Return from the subroutine