Maths (Geometry): TAS3

       Name: TAS3                                                    [Show more]
       Type: Subroutine
   Category: Maths (Geometry)
    Summary: Calculate the dot product of XX15 and an orientation vector
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * DOCKIT calls TAS3
             * TACTICS (Part 3 of 7) calls TAS3
             * TACTICS (Part 7 of 7) calls TAS3


 Calculate the dot product of the vector in XX15 and one of the orientation
 vectors, as determined by the value of Y. If vect is the orientation vector,
 we calculate this:

   (A X) = vect . XX15
         = vect_x * XX15 + vect_y * XX15+1 + vect_z * XX15+2


 Arguments:

   Y                    The orientation vector:

                          * If Y = 10, calculate nosev . XX15

                          * If Y = 16, calculate roofv . XX15

                          * If Y = 22, calculate sidev . XX15


 Returns:

   (A X)                The result of the dot product


.TAS3

 LDX INWK,Y             ; Set Q = the Y-th byte of INWK, i.e. vect_x
 STX Q

 LDA XX15               ; Set A = XX15

 JSR MULT12             ; Set (S R) = Q * A
                        ;           = vect_x * XX15

 LDX INWK+2,Y           ; Set Q = the Y+2-th byte of INWK, i.e. vect_y
 STX Q

 LDA XX15+1             ; Set A = XX15+1

 JSR MAD                ; Set (A X) = Q * A + (S R)
                        ;           = vect_y * XX15+1 + vect_x * XX15

 STA S                  ; Set (S R) = (A X)
 STX R

 LDX INWK+4,Y           ; Set Q = the Y+2-th byte of INWK, i.e. vect_z
 STX Q

 LDA XX15+2             ; Set A = XX15+2

                        ; Fall through into MAD to set:
                        ;
                        ;   (A X) = Q * A + (S R)
                        ;           = vect_z * XX15+2 + vect_y * XX15+1 +
                        ;             vect_x * XX15