Routines
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DD99: Which way is the knight from a record?
Used by the routine at STEER.
The facing that points most nearly at the knight: along V if he is at least as far away in V as in U, along U if further in U, the sign from the difference.
Input
IX The record
Output
A 0 +V, 1 +U, 2 -V, 3 -U: the facing towards him, divided by $40
KNIGHT_DIRECTION DD99 LD HL,(KNIGHT_U) His U less its U; DE its size
DD9C LD E,(IX+$01)
DD9F LD D,(IX+$02)
DDA2 AND A
DDA3 SBC HL,DE
DDA5 PUSH HL
DDA6 BIT 7,H
DDA8 CALL NZ,NEGATE_HL
DDAB EX DE,HL His V less its V; HL its size
DDAC LD HL,(KNIGHT_V)
DDAF LD C,(IX+$03)
DDB2 LD B,(IX+$04)
DDB5 AND A
DDB6 SBC HL,BC
DDB8 PUSH HL
DDB9 BIT 7,H
DDBB CALL NZ,NEGATE_HL
DDBE AND A Further in V (or as far)? A=0, HL the V difference
DDBF SBC HL,DE
DDC1 LD A,$00
DDC3 POP HL
DDC4 POP DE
DDC5 JR NC,KNIGHT_DIRECTION_0
DDC7 INC A Further in U: A=1, HL the U difference
DDC8 EX DE,HL
KNIGHT_DIRECTION_0 DDC9 BIT 7,H Negative: 2 on
DDCB RET Z
DDCC ADD A,$02
DDCE RET
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