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Maths (Arithmetic): MAS3

[Acorn Electron version]

Name: MAS3 [Show more] Type: Subroutine Category: Maths (Arithmetic) Summary: Calculate A = x_hi^2 + y_hi^2 + z_hi^2 in the K% block
Context: See this subroutine in context in the source code References: This subroutine is called as follows: * Main flight loop (Part 15 of 16) calls MAS3

Given a value in Y that points to the start of a ship data block as an offset from K%, calculate the following: A = x_hi^2 + y_hi^2 + z_hi^2 returning A = &FF if the calculation overflows a one-byte result. The K% workspace contains the ship data blocks, so the offset in Y must be 0 or a multiple of NI% (as each block in K% contains NI% bytes).
Arguments: Y The offset from K% for the start of the ship data block to use Returns A A = x_hi^2 + y_hi^2 + z_hi^2 A = &FF if the calculation overflows a one-byte result
.MAS3 LDA K%+1,Y \ Set (A P) = x_hi * x_hi JSR SQUA2 STA R \ Store A (high byte of result) in R LDA K%+4,Y \ Set (A P) = y_hi * y_hi JSR SQUA2 ADC R \ Add A (high byte of second result) to R BCS MA30 \ If the addition of the two high bytes caused a carry \ (i.e. they overflowed), jump to MA30 to return A = &FF STA R \ Store A (sum of the two high bytes) in R LDA K%+7,Y \ Set (A P) = z_hi * z_hi JSR SQUA2 ADC R \ Add A (high byte of third result) to R, so R now \ contains the sum of x_hi^2 + y_hi^2 + z_hi^2 BCC P%+4 \ If there is no carry, skip the following instruction \ to return straight from the subroutine .MA30 LDA #&FF \ The calculation has overflowed, so set A = &FF RTS \ Return from the subroutine