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Elite on the BBC Micro

Maths (Geometry): TAS3 (Disc version)

Name: TAS3 [View in context] Type: Subroutine [Compare versions] Category: Maths (Geometry) Summary: Calculate the dot product of XX15 and an orientation vector
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