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Elite on the BBC Micro

Maths (Arithmetic): FMLTU2 [Elite-A, Parasite]

Name: FMLTU2 [Show more] Type: Subroutine Category: Maths (Arithmetic) Summary: Calculate A = K * sin(A) Deep dive: The sine, cosine and arctan tables
Context: See this subroutine in context in the source code References: This subroutine is called as follows: * CIRCLE2 calls FMLTU2

Calculate the following: A = K * sin(A) Because this routine uses the sine lookup table SNE, we can also call this routine to calculate cosine multiplication. To calculate the following: A = K * cos(B) call this routine with B + 16 in the accumulator, as sin(B + 16) = cos(B).
.FMLTU2 AND #%00011111 \ Restrict A to bits 0-5 (so it's in the range 0-31) TAX \ Set Q = sin(A) * 256 LDA SNE,X STA Q LDA K \ Set A to the radius in K \ Fall through into FMLTU to do the following: \ \ (A ?) = A * Q \ = K * sin(A) * 256 \ \ which is equivalent to: \ \ A = K * sin(A)