Routines
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42136: Test Cell In Direction
Used by the routine at ChooseDirection.
Finds the type of the cell next to an entity in a direction, and tests whether a program packet could go there. The directions are 0 for the lower X cell, 1 for the higher Y cell, 2 for the higher X cell and 3 for the lower Y cell.
Input
A Direction
F The zero flag is set if the direction is zero
DE X position
HL Y position
Output
IY Address of the cell
F The zero flag is set if the packet could go to the cell
A The type of the cell
TestCellInDirection 42136 LD C,A Keep the direction.
42137 PUSH DE Save the position.
42138 PUSH HL
42139 JR Z,TestCellInDirection_X1 Jump if the direction is zero.
42141 DEC A Jump if the direction is one.
42142 JR Z,TestCellInDirection_Y1
42144 DEC A Jump if the direction is two.
42145 JR Z,TestCellInDirection_X2
42147 DEC H Otherwise use the lower Y cell.
TestCellInDirection_Cell 42148 CALL FindMapCell Find the cell using FindMapCell.
42151 PUSH HL Copy its address into IY.
42152 POP IY
42154 POP HL Restore the position.
42155 POP DE
42156 AND A Return with the zero flag set if the cell is empty (type 0).
42157 RET Z
42158 CP 15 Return with the zero flag set if the type is 15.
42160 RET Z
42161 CP 1 Return with the zero flag set if the type is 1.
42163 RET Z
42164 CP 7 Return with the zero flag set if the type is 7.
42166 RET Z
42167 CP 9 Compare the type with 9, and return.
42169 RET
TestCellInDirection_X1 42170 DEC D Use the lower X cell, and jump back.
42171 JR TestCellInDirection_Cell
TestCellInDirection_Y1 42173 INC H Use the higher Y cell, and jump back.
42174 JR TestCellInDirection_Cell
TestCellInDirection_X2 42176 INC D Use the higher X cell, and jump back.
42177 JR TestCellInDirection_Cell
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