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Elite on the BBC Micro

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

Name: TAS3, Removed [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: No direct references to this subroutine in this source file

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
\ --- Mod: Original Acornsoft code removed: -----------> \.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 \ --- End of removed code ----------------------------->