Skip to navigation

Elite on the BBC Micro

Maths (Geometry): TAS3 [Elite-A, Parasite]

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: * TACTICS (Part 7 of 7) calls TAS3 * DOCKIT calls entry point TAS3-2 * TACTICS (Part 3 of 7) calls entry point TAS3-2 * TACTICS (Part 7 of 7) calls entry point TAS3-2

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 Other entry points: TAS3-2 Calculate nosev . XX15
LDY #10 \ Set Y = 10 so we calculate nosev . XX15 .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 JMP MAD \ Call MAD to calculate: \ \ (A X) = Q * A + (S R) \ = vect_z * XX15+2 + vect_y * XX15+1 + \ vect_x * XX15 \ \ and return from the subroutine using a tail call