DOSPLUS 3.5 for the Model III - CRUNCH/CMD Disassembled

CRUNCH/CMD

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DOSPLUS 3.5 CRUNCH/CMD Disassembly - The BASIC Program Cruncher (Model III)

CRUNCH/CMD makes a BASIC program smaller: it copies a program file to a new file without the spaces and the remarks. It is run from the DOS command level as CRUNCH source destination (LINE); its heading reads CRUNCH - BASIC program cruncher - 1.7. It is a load module of 2 blocks, 431 bytes, at 5200H-53AEH with the transfer address 5200H, after the two comment records (the name CRUNCH and the copyright notice). CRUNCH/CMD is on the Model III master only.

The Parts of CRUNCH/CMD

How CRUNCH Works

FSPEC@ takes the source and the destination; a device (@) for either is the error Illegal filespec (5211H). PARAM@ takes LINE, whose value goes straight into the operand of an LD BC (528BH). The source is opened by OPEN@ and the destination by INIT@, both with a buffer of 256 bytes; the source must start with FFH, the mark of a tokenized BASIC program, else Incorrect file type is shown and CRUNCH ends through ABORT@ (524CH). The program is read and written a byte at a time through the ROM's 0013H and 001BH.

For each line (525CH) the link is read and dropped: the destination gets FFFFH for every link, for BASIC to rebuild when it loads the program, and the line number is kept. Outside strings and DATA statements every space is left out (530DH). A string in quotation marks, and DATA with everything after it on the line, are copied as they are (52BBH, 52D8H). REM (93H), and a colon before it, as in the apostrophe (stored :REM'), end the line: the remark is left out (52EFH). Colons in a row are written as one (52F6H). A line that is empty, or holds only a remark, is left out of the program; with LINE given (any value but 0) it is kept with its number and no text, so that a GOTO or GOSUB to it still finds it (528BH). At the link 0000H CRUNCH writes the end of the program, closes the destination and returns to the DOS; the source file is not closed (5266H).

A Line That Starts With a Colon

The test for remarks and colons writes the one colon it keeps as soon as it has passed the colons (5304H). For the first character of a line this happens before the link and the number of the line are written (5283H): a line whose text starts with a colon that is not followed by a remark (10 :PRINT, or a line of colons only) puts a colon byte in front of its link in the destination, or, when the line is then left out, in front of the next line's link, so that the destination is no longer a valid program. A line that starts with a remark after a colon, as the apostrophe, is not affected.

Differences from the Manual

The manual has no section on CRUNCH; it names the utility only in a JCL example (CRUNCH $FILE/BAS $FILE/CRN). Everything on this page comes from the bytes.

5200H - CRUNCH

CRUNCH/CMD's transfer address, entered from the DOS command level with Register Pair HL at the command line after the word CRUNCH: CRUNCH source destination (LINE). Both files are BASIC programs in the tokenized form of Disk BASIC (the first byte FFH). CRUNCH copies the source to the destination line by line without the spaces outside strings and DATA statements, without the remarks (REM and the apostrophe), and with repeated colons made one; a line that is empty or only a remark is left out, or kept with its number and no text when LINE is given. It ends at RET to the DOS after closing the destination.

5259H - The Lines

5259H writes the byte in Register A: the FFH of the file, and after each line its ending 00H. Each line of the source starts with its link (two bytes) and its number (two bytes); a link of 0000H ends the program. The link is not copied: each line of the destination gets the link FFFFH, which BASIC rebuilds when it loads the program.

52B2H - The Text of a Line

The characters of a line, past spaces (530DH); 00H ends the line (written at 5259H). The DATA token (88H) and a string in quotation marks are copied as they are, spaces and all; a remark (REM, 93H, or a colon before it) ends the line; repeated colons are written as one.

52EBH - Remarks and Colons

52EBH reads the next character past spaces first; 52EFH tests the character in Register A. Returns the C FLAG at the end of the line (Register A = 00H), the Z FLAG for a remark (REM, 93H, also after a colon, as in the apostrophe :REM'), else the NZ FLAG with a character in Register A. A colon and the colons right after it are written as one colon (5304H) before the character that follows them.

530DH - Read Past Spaces

Reads the bytes of the source until one is not a space: Register A returns it, with the C FLAG and the Z FLAG for the 00H that ends a line, else the NZ FLAG and no C FLAG.

5319H - Read and Write a Byte

5319H reads a byte of the source through the ROM's 0013H with the file control block at 53AFH, 5325H writes Register A to the destination through 001BH with the file control block at 53CFH; an error goes to 5336H.

5331H - The Errors

5331H the error 2CH, Illegal filespec; 5334H, inside the LD BC at 5333H, the error 2EH, Invalid parameter; 5336H any error code in Register A. Each is posted with bit 6 set, so ERROR@ shows the message without its frame, and with bit 7 clear, so ERROR@ ends through ABORT@.