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BBC Micro Elite

Maths (Arithmetic): TIS3

Name: TIS3 [View in context] Type: Subroutine Category: Maths (Arithmetic) Summary: Calculate -(nosev_1 * roofv_1 + nosev_2 * roofv_2) / nosev_3
Calculate the following expression: A = -(nosev_1 * roofv_1 + nosev_2 * roofv_2) / nosev_3 where 1, 2 and 3 are x, y, or z, depending on the values of X, Y and A. This routine is called with the following values: X = 0, Y = 2, A = 4 -> A = -(nosev_x * roofv_x + nosev_y * roofv_y) / nosev_z X = 0, Y = 4, A = 2 -> A = -(nosev_x * roofv_x + nosev_z * roofv_z) / nosev_y X = 2, Y = 4, A = 0 -> A = -(nosev_y * roofv_y + nosev_z * roofv_z) / nosev_x Arguments: X Index 1 (0 = x, 2 = y, 4 = z) Y Index 2 (0 = x, 2 = y, 4 = z) A Index 3 (0 = x, 2 = y, 4 = z)
.TIS3 STA P+2 \ Store P+2 in A for later LDA INWK+10,X \ Set Q = nosev_x_hi (plus X) STA Q LDA INWK+16,X \ Set A = roofv_x_hi (plus X) JSR MULT12 \ Set (S R) = Q * A \ = nosev_x_hi * roofv_x_hi LDX INWK+10,Y \ Set Q = nosev_x_hi (plus Y) STX Q LDA INWK+16,Y \ Set A = roofv_x_hi (plus Y) JSR MAD \ Set (A X) = Q * A + (S R) \ = (nosev_x,X * roofv_x,X) + \ (nosev_x,Y * roofv_x,Y) STX P \ Store low byte of result in P, so result is now in \ (A P) LDY P+2 \ Set Q = roofv_x_hi (plus argument A) LDX INWK+10,Y STX Q EOR #%10000000 \ Flip the sign of A \ Fall through into DIVDT to do: \ \ (P+1 A) = (A P) / Q \ \ = -((nosev_x,X * roofv_x,X) + \ (nosev_x,Y * roofv_x,Y)) \ / nosev_x,A