Routines
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E020: Cut a step in -U short at a box of a cell
Used by the routine at CLIP_MINUS_U.
As CUT_STEP_PLUS_U, for the -U routine (CLIP_MINUS_U): the overlap is made positive, so that it shortens a negative step.
Input
D The column of the cell to test
H Its row
IX The object
Output
F Carry set if the step was cut
CUT_STEP_MINUS_U E020 CALL HIT_BOXES_U Test the cell's boxes; nothing in the way returns with carry clear
E023 RET NC
E024 NEG Plus the overlap, and cut the step
E026 JR CUT_STEP_U
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