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Routines |
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Whenever an area has to be 'made' or 'reclaimed' the system variables that address locations beyond the 'position' of the change have to be amended as required. On entry the BC register pair holds the number of bytes involved and the HL register pair addresses the location before the 'position'.
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| POINTERS | 1664 | PUSH AF | These registers are saved. | |||||||
| 1665 | PUSH HL | Copy the address of the 'position'. | ||||||||
| 1666 | LD HL,$5C4B | This is VARS, the first of the fourteen system pointers. | ||||||||
| 1669 | LD A,$0E | |||||||||
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A loop is now entered to consider each pointer in turn. Only those pointers that point beyond the 'position' are changed.
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| PTR_NEXT | 166B | LD E,(HL) | Fetch the two bytes of the current pointer. | |||||||
| 166C | INC HL | |||||||||
| 166D | LD D,(HL) | |||||||||
| 166E | EX (SP),HL | Exchange the system variable with the address of the 'position'. | ||||||||
| 166F | AND A | The carry flag will become set if the system variable's address is to be updated. | ||||||||
| 1670 | SBC HL,DE | |||||||||
| 1672 | ADD HL,DE | |||||||||
| 1673 | EX (SP),HL | Restore the 'position'. | ||||||||
| 1674 | JR NC,PTR_DONE | Jump forward if the pointer is to be left; otherwise change it. | ||||||||
| 1676 | PUSH DE | Save the old value. | ||||||||
| 1677 | EX DE,HL | Now add the value in BC to the old value. | ||||||||
| 1678 | ADD HL,BC | |||||||||
| 1679 | EX DE,HL | |||||||||
| 167A | LD (HL),D | Enter the new value into the system variable - high byte before low byte. | ||||||||
| 167B | DEC HL | |||||||||
| 167C | LD (HL),E | |||||||||
| 167D | INC HL | Point again to the high byte. | ||||||||
| 167E | POP DE | Fetch the old value. | ||||||||
| PTR_DONE | 167F | INC HL | Point to the next system variable and jump back until all fourteen have been considered. | |||||||
| 1680 | DEC A | |||||||||
| 1681 | JR NZ,PTR_NEXT | |||||||||
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Now find the size of the block to be moved.
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| 1683 | EX DE,HL | Put the old value of STKEND in HL and restore the other registers. | ||||||||
| 1684 | POP DE | |||||||||
| 1685 | POP AF | |||||||||
| 1686 | AND A | Now find the difference between the old value of STKEND and the 'position'. | ||||||||
| 1687 | SBC HL,DE | |||||||||
| 1689 | LD B,H | Transfer the result to BC and add 1 for the inclusive byte. | ||||||||
| 168A | LD C,L | |||||||||
| 168B | INC BC | |||||||||
| 168C | ADD HL,DE | Reform the old value of STKEND and pass it to DE before returning. | ||||||||
| 168D | EX DE,HL | |||||||||
| 168E | RET | |||||||||
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