Maths (Arithmetic): Negate16Bit

       Name: Negate16Bit                                             [Show more]
       Type: Subroutine
   Category: Maths (Arithmetic)
    Summary: Negate a 16-bit number
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * ApplyTyreForces calls Negate16Bit
             * ProcessDrivingKeys (Part 2 of 6) calls Negate16Bit
             * AssistSteering calls via Negate16Bit+2
             * ProcessDrivingKeys (Part 2 of 6) calls via Negate16Bit+2
             * SubtractCoords calls via Negate16Bit+2


 This routine negates the 16-bit number (A T).


 Other entry points:

   Negate16Bit+2        Set (A T) = -(U T)


.Negate16Bit

 STA U                  \ Set (U T) = (A T)

 LDA #0                 \ Set (A T) = 0 - (U T)
 SEC                    \           = -(A T)
 SBC T                  \
 STA T                  \ starting with the low bytes

 LDA #0                 \ And then the high bytes
 SBC U

 RTS                    \ Return from the subroutine