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BBC Micro Elite

Moving: MVEIT (Part 4 of 9)

Name: MVEIT (Part 4 of 9) [View in context] Type: Subroutine Category: Moving Summary: Move current ship: Apply acceleration to ship's speed as a one-off
This routine has multiple stages. This stage does the following: * Apply acceleration to the ship's speed (if acceleration is non-zero), and then zero the acceleration as it's a one-off change
LDA INWK+27 \ Set A = the ship's speed in byte #24 + the ship's CLC \ acceleration in byte #28 ADC INWK+28 BPL P%+4 \ If the result is positive, skip the following \ instruction LDA #0 \ Set A to 0 to stop the speed from going negative LDY #15 \ Fetch byte #15 from the ship's blueprint, which \ contains the ship's maximum speed CMP (XX0),Y \ If A < the ship's maximum speed, skip the following BCC P%+4 \ instruction LDA (XX0),Y \ Set A to the ship's maximum speed STA INWK+27 \ We have now calculated the new ship's speed after \ accelerating and keeping the speed within the ship's \ limits, so store the updated speed in byte #27 LDA #0 \ We have added the ship's acceleration, so we now set STA INWK+28 \ it back to 0 in byte #28, as it's a one-off change