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Routines |
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Used by the routine at SAVE_ETC.
There are three main parts to this routine.
Start therefore with the loading of the data block.
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ME_CONTRL | 08B6 | LD C,(IX+$0B) | Fetch the 'length' of the data block. | |||||||
08B9 | LD B,(IX+$0C) | |||||||||
08BC | PUSH BC | Save a copy of the 'length'. | ||||||||
08BD | INC BC | Now make 'length+1' locations available in the work space. | ||||||||
08BE | RST $30 | |||||||||
08BF | LD (HL),$80 | Place an end marker in the extra location. | ||||||||
08C1 | EX DE,HL | Move the 'start' pointer to the HL register pair. | ||||||||
08C2 | POP DE | Fetch the original 'length'. | ||||||||
08C3 | PUSH HL | Save a copy of the 'start'. | ||||||||
08C4 | PUSH HL | Now set the IX register pair for the actual load. | ||||||||
08C5 | POP IX | |||||||||
08C7 | SCF | Signal 'LOAD'. | ||||||||
08C8 | LD A,$FF | Signal 'data block only'. | ||||||||
08CA | CALL LD_BLOCK | Load the data block. | ||||||||
The lines of the new program are merged with the lines of the old program.
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08CD | POP HL | Fetch the 'start' of the new program. | ||||||||
08CE | LD DE,($5C53) | Initialise DE to the 'start' of the old program (PROG). | ||||||||
Enter a loop to deal with the lines of the new program.
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ME_NEW_LP | 08D2 | LD A,(HL) | Fetch a line number and test it. | |||||||
08D3 | AND $C0 | |||||||||
08D5 | JR NZ,ME_VAR_LP | Jump when finished with all the lines. | ||||||||
Now enter an inner loop to deal with the lines of the old program.
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ME_OLD_LP | 08D7 | LD A,(DE) | Fetch the high line number byte and compare it. Jump forward if it does not match but in any case advance both pointers. | |||||||
08D8 | INC DE | |||||||||
08D9 | CP (HL) | |||||||||
08DA | INC HL | |||||||||
08DB | JR NZ,ME_OLD_L1 | |||||||||
08DD | LD A,(DE) | Repeat the comparison for the low line number bytes. | ||||||||
08DE | CP (HL) | |||||||||
ME_OLD_L1 | 08DF | DEC DE | Now retreat the pointers. | |||||||
08E0 | DEC HL | |||||||||
08E1 | JR NC,ME_NEW_L2 | Jump forward if the correct place has been found for a line of the new program. | ||||||||
08E3 | PUSH HL | Otherwise find the address of the start of the next old line. | ||||||||
08E4 | EX DE,HL | |||||||||
08E5 | CALL NEXT_ONE | |||||||||
08E8 | POP HL | |||||||||
08E9 | JR ME_OLD_LP | Go round the loop for each of the 'old lines'. | ||||||||
ME_NEW_L2 | 08EB | CALL ME_ENTER | Enter the 'new line' and go round the outer loop again. | |||||||
08EE | JR ME_NEW_LP | |||||||||
In a similar manner the variables of the new program are merged with the variables of the old program.
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ME_VAR_LP | 08F0 | LD A,(HL) | Fetch each variable name in turn and test it. | |||||||
08F1 | LD C,A | |||||||||
08F2 | CP $80 | Return when all the variables have been considered. | ||||||||
08F4 | RET Z | |||||||||
08F5 | PUSH HL | Save the current new pointer. | ||||||||
08F6 | LD HL,($5C4B) | Fetch VARS (for the old program). | ||||||||
Now enter an inner loop to search the existing variables area.
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ME_OLD_VP | 08F9 | LD A,(HL) | Fetch each variable name and test it. | |||||||
08FA | CP $80 | |||||||||
08FC | JR Z,ME_VAR_L2 | Jump forward once the end marker is found. (Make an 'addition'.) | ||||||||
08FE | CP C | Compare the names (first bytes). | ||||||||
08FF | JR Z,ME_OLD_V2 | Jump forward to consider it further, returning here if it proves not to match fully. | ||||||||
ME_OLD_V1 | 0901 | PUSH BC | Save the new variable's name whilst the next 'old variable' is located. | |||||||
0902 | CALL NEXT_ONE | |||||||||
0905 | POP BC | |||||||||
0906 | EX DE,HL | Restore the pointer to the DE register pair and go round the loop again. | ||||||||
0907 | JR ME_OLD_VP | |||||||||
The old and new variables match with respect to their first bytes but variables with long names will need to be matched fully.
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ME_OLD_V2 | 0909 | AND $E0 | Consider bits 7, 6 and 5 only. | |||||||
090B | CP $A0 | Accept all the variable types except 'long named variables'. | ||||||||
090D | JR NZ,ME_VAR_L1 | |||||||||
090F | POP DE | Make DE point to the first character of the 'new name'. | ||||||||
0910 | PUSH DE | |||||||||
0911 | PUSH HL | Save the pointer to the 'old name'. | ||||||||
Enter a loop to compare the letters of the long names.
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ME_OLD_V3 | 0912 | INC HL | Update both the 'old' and the 'new' pointers. | |||||||
0913 | INC DE | |||||||||
0914 | LD A,(DE) | Compare the two letters. | ||||||||
0915 | CP (HL) | |||||||||
0916 | JR NZ,ME_OLD_V4 | Jump forward if the match fails. | ||||||||
0918 | RLA | Go round the loop until the 'last character' is found. | ||||||||
0919 | JR NC,ME_OLD_V3 | |||||||||
091B | POP HL | Fetch the pointer to the start of the 'old' name and jump forward - successful. | ||||||||
091C | JR ME_VAR_L1 | |||||||||
ME_OLD_V4 | 091E | POP HL | Fetch the pointer and jump back - unsuccessful. | |||||||
091F | JR ME_OLD_V1 | |||||||||
Come here if the match was found.
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ME_VAR_L1 | 0921 | LD A,$FF | Signal 'replace' variable. | |||||||
And here if not. (A holds +80 - variable to be 'added'.)
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ME_VAR_L2 | 0923 | POP DE | Fetch pointer to 'new' name. | |||||||
0924 | EX DE,HL | Switch over the registers. | ||||||||
0925 | INC A | The zero flag is to be set if there is to be a 'replacement', reset for an 'addition'. | ||||||||
0926 | SCF | Signal 'handling variables'. | ||||||||
0927 | CALL ME_ENTER | Now make the entry. | ||||||||
092A | JR ME_VAR_LP | Go round the loop to consider the next new variable. |
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