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Notes on Coding of BBC BASIC and GW-BASIC Files - Martin Carradus July 1993 --------------------------------------------------------------------------- *** I do not guarantee the accuracy of the following information *** These notes give details of the format of files produced with BBC BASIC and GW-BASIC when the BASIC program is saved to disc. (BASIC command SAVE"filename", where 'filename' is the name of the file to be saved to). Introduction ------------ In order to understand these notes, you will need to know something about the difference between compilers and interpreters. All computer languages need to be translated into the fundamental instructions of the particular computer (machine code). A compiler is presented with the complete program and translates the whole thing into machine code. The machine code is then run on the computer in a separate stage. An interpreter, however, translates the program and obeys it as it goes along. The advantage is that you do not need a preceding stage before you run the program. The disadvantage is that, since the whole program has not been 'seen', the final code is usually less efficient and runs more slowly than compiled code. In order for an interpreter to obey the program efficiently, it is usually coded so that it makes it easier to work out parts of the program. The main 'trick' is to code the keywords (words like GOTO, or IF or PRINT) into only a couple of characters (bytes), known as a token. This means that they can be easily recognised every time the interpreter runs across them in the program. At the beginning of each line of the program, the interpreter will need to know the line number of that line and where the next line is. Both are coded for greater efficiency. All types of BASIC use an interpreter. In these notes Hex is Hexadecimal, or counting to base 16, Octal is counting to base 8, and Binary is counting to base 2. A byte is enough storage to hold one character and is 8 bits long (bit is a 0 or 1). The low byte is the least significant part of a binary number (lower 8 bits) and the high byte is the most significant (higher 8 bits). The file is assumed to come in from left to right, the earlier the byte, the more to the left it is. ASCII is a standard code for representing characters as bytes. A. Coding of BBC BASIC files ------------------------- This is basically pure ASCII text, apart from line numbers and tokens. The program file begins with a return symbol and ends with ASCII code 255 (hex FF). Each line has the following format:- <Three bytes> <coded BASIC line> <return symbol - ASCII code 13> The starting three bytes have the line number in the first two bytes (high byte first) and the length of the decoded line in the third byte. ------- All the key words in BBC BASIC are coded in either one or two bytes, always starting with a byte with an ASCII value greater than or equal to 127 (decimal). Hence all the tokens apart from that for OTHERWISE (see below) have the top bit set and are unprintable ASCII characters. Apart from that, the line numbers after GOTOs and GOSUBs are preceded by a byte with ASCII code 141 decimal (215 octal - 8D hex) and are coded in rather a strange way:- Line Number: (After ASCII character 141) ----------- Consists of three bytes, the bits of which are as follows (most right most bit is bit 0). (the 'is' Bits refer to the actual line number in binary). Lowest Byte: (Right most) Bit 0 is Bit 8, Bit 1 is Bit 9, Bit 2 is Bit 10, Bit 3 is Bit 11. Bit 4 is Bit 12, Bit 5 is Bit 13, Bit 6 is always 0, Bit 7 is always 1. Middle Byte: Bit 0 is Bit 0, Bit 1 is Bit 2, Bit 2 is Bit 3, Bit 3 is Bit 3. Bit 4 is Bit 4, Bit 5 is Bit 5, Bit 6 is always 0, Bit 7 is always 1. Highest Byte: (Left Most) Bit 0 is always 0, Bit 1 is always 0, Bit 2 is Bit 14, Bit 3 is inverted bit 15. Bit 4 is inverted Bit 6, Bit 5 is Bit 7, Bit 6 is always 0, Bit 7 is always 1. So the middle byte basically codes the low byte of the line number, and the low byte codes the high byte of the line number with bits needed to be added in or inverted and added in from the highest byte of the coding. I coded this conversion in C as follows: If c[0] is the highest byte of the coding (left most) , c[1] is the middle byte of the coding, c[2] is the lowest byte of the coding (right most) and lineno is the integer that is to hold the final decoded line number: c[0]=c[0]^0x14; /* Inverts extra bits (Bits 6 and 15) */ c[1]=c[1]&0x3f; /* Masks off low byte of lineno */ c[2]=c[2]&0x3f; /* Masks off high byte of lineno */ c[1]=c[1] | ((c[0] & 0x30)<<2); /* Adds in Bits 6 and 7 to low byte */ c[2]=c[2] | ((c[0] & 0x0c)<<4); /* Adds in Bits 14 and 15 to high byte */ lineno=(int)c[1] +((int)c[2]<<8); /* Combines low and high bytes of lineno */ Tokens ------ Herewith a complete list of tokens, both in alphabetical order and ASCII code order as held in a C structure: struct list { char bbc_keyword[10]; char bbc_token_hex[3]; char bbc_token_octal[10]; }; /* Alphabetical Order */ struct list token_list[] = { "Line No", "\x8d", "\215", "ABS", "\x94", "\224", "ACS", "\x95", "\225", "ADVAL", "\x96", "\226", "AND", "\x80", "\200", "APPEND", "\xc7\x8e", "\307\216", "ASC", "\x97", "\227", "ASN", "\x98", "\230", "ATN", "\x99", "\231", "AUTO", "\xc7\x8f", "\307\217", "BEAT", "\xc6\x8f", "\306\217", "BEATS", "\xc8\x9e", "\310\236", "BGET", "\x9a", "\232", "BPUT", "\xd5", "\325", "CALL", "\xd6", "\326", "CASE", "\xc8\x8e", "\310\216", "CHAIN", "\xd7", "\327", "CHR$", "\xbd", "\275", "CIRCLE", "\xc8\x8f", "\310\217", "CLEAR", "\xd8", "\330", "CLG", "\xda", "\332", "CLOSE", "\xd9", "\331", "CLS", "\xdb", "\333", "COLOUR", "\xfb", "\373", "COS", "\x9b", "\233", "COUNT", "\x9c", "\234", "DATA", "\xdc", "\334", "DEF", "\xdd", "\335", "DEG", "\x9d", "\235", "DELETE", "\xc7\x90", "\307\220", "DIM", "\xde", "\336", "DIV", "\x81", "\201", "DRAW", "\xdf", "\337", "EDIT", "\xc7\x91", "\307\221", "ELLIPSE", "\xc8\x9d", "\310\235", "ELSE", "\xcc", "\314", "ELSE", "\x8b", "\213", "END", "\xe0", "\340", "ENDCASE", "\xcb", "\313", "ENDIF", "\xcd", "\315", "ENDPROC", "\xe1", "\341", "ENDWHILE", "\xce", "\316", "EOF", "\xc5", "\305", "EOR", "\x82", "\202", "ERL", "\x9e", "\236", "ERR", "\x9f", "\237", "ERROR", "\x85", "\205", "EVAL", "\xa0", "\240", "EXP", "\xa1", "\241", "EXT", "\xa2", "\242", "FALSE", "\xa3", "\243", "FILL", "\xc8\x90", "\310\220", "FN", "\xa4", "\244", "FOR", "\xe3", "\343", "GCOL", "\xe6", "\346", "GET", "\xa5", "\245", "GET$", "\xbe", "\276", "GOSUB", "\xe4", "\344", "GOTO", "\xe5", "\345", "HELP", "\xc7\x92", "\307\222", "HIMEM", "\xd3", "\323", "HIMEM", "\x93", "\223", "IF", "\xe7", "\347", "INKEY", "\xa6", "\246", "INKEY$", "\xbf", "\277", "INPUT", "\xe8", "\350", "INSTALL", "\xc8\x9a", "\310\232", "INSTR(", "\xa7", "\247", "INT", "\xa8", "\250", "LEFT$(", "\xc0", "\300", "LEN", "\xa9", "\251", "LET", "\xe9", "\351", "LIBRARY", "\xc8\x9b", "\310\233", "LINE", "\x86", "\206", "LIST", "\xc7\x93", "\307\223", "LN", "\xaa", "\252", "LOAD", "\xc7\x94", "\307\224", "LOCAL", "\xea", "\352", "LOG", "\xab", "\253", "LOMEM", "\xd2", "\322", "LOMEM", "\x92", "\222", "LVAR", "\xc7\x95", "\307\225", "MID$(", "\xc1", "\301", "MOD", "\x83", "\203", "MODE", "\xeb", "\353", "MOUSE", "\xc8\x97", "\310\227", "MOVE", "\xec", "\354", "NEW", "\xc7\x96", "\307\226", "NEXT", "\xed", "\355", "NOT", "\xac", "\254", "OF", "\xca", "\312", "OFF", "\x87", "\207", "OLD", "\xc7\x97", "\307\227", "ON", "\xee", "\356", "OPENIN", "\x8e", "\216", "OPENOUT", "\xae", "\256", "OPENUP", "\xad", "\255", "OR", "\x84", "\204", "ORIGIN", "\xc8\x91", "\310\221", "OSCLI", "\xff", "\377", "OTHERWISE","\x7f", "\177", "OVERLAY", "\xc8\xa3", "\310\243", "PAGE", "\xd0", "\320", "PAGE", "\x90", "\220", "PI", "\xaf", "\257", "PLOT", "\xf0", "\360", "POINT", "\xc8\x92", "\310\222", "POINT(", "\xb0", "\260", "POS", "\xb1", "\261", "PRINT", "\xf1", "\361", "PROC", "\xf2", "\362", "PTR", "\xcf", "\317", "PTR", "\x8f", "\217", "QUIT", "\xc8\x98", "\310\230", "RAD", "\xb2", "\262", "READ", "\xf3", "\363", "RECTANGLE","\xc8\x93", "\310\223", "REM", "\xf4", "\364", "RENUMBER", "\xc7\x98", "\307\230", "REPEAT", "\xf5", "\365", "REPORT", "\xf6", "\366", "RESTORE", "\xf7", "\367", "RETURN", "\xf8", "\370", "RIGHT$(", "\xc2", "\302", "RND", "\xb3", "\263", "RUN", "\xf9", "\371", "SAVE", "\xc7\x99", "\307\231", "SGN", "\xb4", "\264", "SIN", "\xb5", "\265", "SOUND", "\xd4", "\324", "SPC", "\x89", "\211", "SQR", "\xb6", "\266", "STEP", "\x88", "\210", "STEREO", "\xc8\xa2", "\310\242", "STOP", "\xfa", "\372", "STR$", "\xc3", "\303", "STRING$(", "\xc4", "\304", "SUM", "\xc6\x8e", "\306\216", "SWAP", "\xc8\x94", "\310\224", "SYS", "\xc8\x99", "\310\231", "TAB(", "\x8a", "\212", "TAN", "\xb7", "\267", "TEMPO", "\xc8\x9f", "\310\237", "THEN", "\x8c", "\214", "TIME", "\xd1", "\321", "TIME", "\x91", "\221", "TINT", "\xc8\x9c", "\310\234", "TO", "\xb8", "\270", "TOP", "\xb8P", "\270P", "TRACE", "\xfc", "\374", "TRUE", "\xb9", "\271", "TWIN", "\xc7\x9a", "\307\232", "TWINO", "\xc7\x9b", "\307\233", "UNTIL", "\xfd", "\375", "USR", "\xba", "\272", "VAL", "\xbb", "\273", "VDU", "\xef", "\357", "VOICE", "\xc8\xa1", "\310\241", "VOICES", "\xc8\xa0", "\310\240", "VPOS", "\xbc", "\274", "WAIT", "\xc8\x96", "\310\226", "WHEN", "\xc9", "\311", "WHILE", "\xc8\x95", "\310\225", "WIDTH", "\xfe", "\376", "", "", ""}; /* Sorted token value order */ struct list sort_token_list= { "OTHERWISE","\x7f", "\177", "AND", "\x80", "\200", "DIV", "\x81", "\201", "EOR", "\x82", "\202", "MOD", "\x83", "\203", "OR", "\x84", "\204", "ERROR", "\x85", "\205", "LINE", "\x86", "\206", "OFF", "\x87", "\207", "STEP", "\x88", "\210", "SPC", "\x89", "\211", "TAB(", "\x8a", "\212", "ELSE", "\x8b", "\213", "THEN", "\x8c", "\214", "Line No", "\x8d", "\215", "OPENIN", "\x8e", "\216", "PTR", "\x8f", "\217", "PAGE", "\x90", "\220", "TIME", "\x91", "\221", "LOMEM", "\x92", "\222", "HIMEM", "\x93", "\223", "ABS", "\x94", "\224", "ACS", "\x95", "\225", "ADVAL", "\x96", "\226", "ASC", "\x97", "\227", "ASN", "\x98", "\230", "ATN", "\x99", "\231", "BGET", "\x9a", "\232", "COS", "\x9b", "\233", "COUNT", "\x9c", "\234", "DEG", "\x9d", "\235", "ERL", "\x9e", "\236", "ERR", "\x9f", "\237", "EVAL", "\xa0", "\240", "EXP", "\xa1", "\241", "EXT", "\xa2", "\242", "FALSE", "\xa3", "\243", "FN", "\xa4", "\244", "GET", "\xa5", "\245", "INKEY", "\xa6", "\246", "INSTR(", "\xa7", "\247", "INT", "\xa8", "\250", "LEN", "\xa9", "\251", "LN", "\xaa", "\252", "LOG", "\xab", "\253", "NOT", "\xac", "\254", "OPENUP", "\xad", "\255", "OPENOUT", "\xae", "\256", "PI", "\xaf", "\257", "POINT(", "\xb0", "\260", "POS", "\xb1", "\261", "RAD", "\xb2", "\262", "RND", "\xb3", "\263", "SGN", "\xb4", "\264", "SIN", "\xb5", "\265", "SQR", "\xb6", "\266", "TAN", "\xb7", "\267", "TO", "\xb8", "\270", "TOP", "\xb8P", "\270P", "TRUE", "\xb9", "\271", "USR", "\xba", "\272", "VAL", "\xbb", "\273", "VPOS", "\xbc", "\274", "CHR$", "\xbd", "\275", "GET$", "\xbe", "\276", "INKEY$", "\xbf", "\277", "LEFT$(", "\xc0", "\300", "MID$(", "\xc1", "\301", "RIGHT$(", "\xc2", "\302", "STR$", "\xc3", "\303", "STRING$(", "\xc4", "\304", "EOF", "\xc5", "\305", "SUM", "\xc6\x8e", "\306\216", "BEAT", "\xc6\x8f", "\306\217", "APPEND", "\xc7\x8e", "\307\216", "AUTO", "\xc7\x8f", "\307\217", "DELETE", "\xc7\x90", "\307\220", "EDIT", "\xc7\x91", "\307\221", "HELP", "\xc7\x92", "\307\222", "LIST", "\xc7\x93", "\307\223", "LOAD", "\xc7\x94", "\307\224", "LVAR", "\xc7\x95", "\307\225", "NEW", "\xc7\x96", "\307\226", "OLD", "\xc7\x97", "\307\227", "RENUMBER", "\xc7\x98", "\307\230", "SAVE", "\xc7\x99", "\307\231", "TWIN", "\xc7\x9a", "\307\232", "TWINO", "\xc7\x9b", "\307\233", "CASE", "\xc8\x8e", "\310\216", "CIRCLE", "\xc8\x8f", "\310\217", "FILL", "\xc8\x90", "\310\220", "ORIGIN", "\xc8\x91", "\310\221", "POINT", "\xc8\x92", "\310\222", "RECTANGLE","\xc8\x93", "\310\223", "SWAP", "\xc8\x94", "\310\224", "WHILE", "\xc8\x95", "\310\225", "WAIT", "\xc8\x96", "\310\226", "MOUSE", "\xc8\x97", "\310\227", "QUIT", "\xc8\x98", "\310\230", "SYS", "\xc8\x99", "\310\231", "INSTALL", "\xc8\x9a", "\310\232", "LIBRARY", "\xc8\x9b", "\310\233", "TINT", "\xc8\x9c", "\310\234", "ELLIPSE", "\xc8\x9d", "\310\235", "BEATS", "\xc8\x9e", "\310\236", "TEMPO", "\xc8\x9f", "\310\237", "VOICES", "\xc8\xa0", "\310\240", "VOICE", "\xc8\xa1", "\310\241", "STEREO", "\xc8\xa2", "\310\242", "OVERLAY", "\xc8\xa3", "\310\243", "WHEN", "\xc9", "\311", "OF", "\xca", "\312", "ENDCASE", "\xcb", "\313", "ELSE", "\xcc", "\314", "ENDIF", "\xcd", "\315", "ENDWHILE", "\xce", "\316", "PTR", "\xcf", "\317", "PAGE", "\xd0", "\320", "TIME", "\xd1", "\321", "LOMEM", "\xd2", "\322", "HIMEM", "\xd3", "\323", "SOUND", "\xd4", "\324", "BPUT", "\xd5", "\325", "CALL", "\xd6", "\326", "CHAIN", "\xd7", "\327", "CLEAR", "\xd8", "\330", "CLOSE", "\xd9", "\331", "CLG", "\xda", "\332", "CLS", "\xdb", "\333", "DATA", "\xdc", "\334", "DEF", "\xdd", "\335", "DIM", "\xde", "\336", "DRAW", "\xdf", "\337", "END", "\xe0", "\340", "ENDPROC", "\xe1", "\341", "FOR", "\xe3", "\343", "GOSUB", "\xe4", "\344", "GOTO", "\xe5", "\345", "GCOL", "\xe6", "\346", "IF", "\xe7", "\347", "INPUT", "\xe8", "\350", "LET", "\xe9", "\351", "LOCAL", "\xea", "\352", "MODE", "\xeb", "\353", "MOVE", "\xec", "\354", "NEXT", "\xed", "\355", "ON", "\xee", "\356", "VDU", "\xef", "\357", "PLOT", "\xf0", "\360", "PRINT", "\xf1", "\361", "PROC", "\xf2", "\362", "READ", "\xf3", "\363", "REM", "\xf4", "\364", "REPEAT", "\xf5", "\365", "REPORT", "\xf6", "\366", "RESTORE", "\xf7", "\367", "RETURN", "\xf8", "\370", "RUN", "\xf9", "\371", "STOP", "\xfa", "\372", "COLOUR", "\xfb", "\373", "TRACE", "\xfc", "\374", "UNTIL", "\xfd", "\375", "WIDTH", "\xfe", "\376", "OSCLI", "\xff", "\377", "", "", ""}; NB LOMEM, HIMEM, PAGE, PTR and TIME have different tokens depending -- on whether they are statement or function tokens (whether they are given or give a value). The token for ELSE has different values depending on whether it is part of an IF statement on one line or spread over several lines. Also the keyword 'BY' is not tokenised. Note the token for 'TOP', which is that for 'TO' with a 'P' after it. B. Coding of GW-BASIC Files ------------------------ The format of a GW-BASIC file is as follows: <Hex FF> lines <Hex 00 00 FF FF 1A> or sometimes terminated with <Hex 00 00 FF 1A> The lines are coded as follows: <Four bytes> coded line <Hex 00> The first four bytes hold the following information: First two bytes: The position of the next line in the file. Second two bytes: The line number. The line number is coded as a binary number, the lowest byte first. The position of the next line is with an added offset. If the first byte of the file is regarded as byte 0, then the position given is that of the first of the next four bytes plus 4686 (decimal) (124E Hex). ---- The coded position is given low byte first, high byte second. Thus if the first line was line number ten and the second line begins at file byte position 7, then the first four bytes of the file after the leading FF are:- Hex 55 12 0A 00 The Line -------- The coded line has the following components: Line Numbers, Keyword Tokens, String Literals, Operators, Integers, Hex Literals, Octal Literals and Floating Point Literals. 1. Line Numbers (after GOTO or GOSUB) ------------ Are 'announced' by the character ASCII value 14 (Hex 0E, Octal 16) It is simply the binary value of the line number in two bytes, low byte first. 2. String Literals (Strings of characters enclosed in double quotes) --------------- Are entirely uncoded. Even characters that might be regarded as tokens are ignored by the BASIC interpreter. 3. Operators (i.e. for addition, subtraction etc.) --------- These are coded (they do not take their ASCII character value). They are: Operator Hex Token Octal Token -------- --------- ----------- ">", "\xe6", "\346", "=", "\xe7", "\347", "<", "\xe8", "\350", "+", "\xe9", "\351", "-", "\xea", "\352", "*", "\xeb", "\353", "/", "\xec", "\354", "^", "\xed", "\355", "AND", "\xee", "\356", "OR", "\xef", "\357", "XOR", "\xf0", "\360", "EQV", "\xf1", "\361", "IMP", "\xf2", "\362", "MOD", "\xf3", "\363", "\\", "\xf4", "\364", (backslash) "NOT", "\xd3", "\323" 4. Integer Literals (a sequence of numeric characters e.g. 259 ) ---------------- These are coded in a different way depending on whether the number is less than ten, greater than nine and less than 256, or greater than 255. Less than ten. ------------- Coded as single byte which has the ASCII value of 17 + the numeric value, hence: 0 is coded as a byte with ASCII code 17 (decimal). 1 " " " " " " " " 18 2 " " " " " " " " 19 ..... 9 " " " " " " " " 26 Greater than 9 and less than 256 -------------------------------- Coded as a single byte preceded by a byte with ASCII code 15 (Hex 0F Octal 17). The byte simply holds the numeric value. Greater than 255 ---------------- Coded in two bytes preceded by a byte with ASCII code 28 (decimal) (Hex 1C, Octal 34). The two bytes simply hold the numeric value, low byte first. 5. Hex Literals (a string of hex characters preceded by &H e.g. &HF1) ------------ Converted to their binary representation, then coded in a similar way to integers greater than 255 and preceded by a character with ASCII code 12 (Hex 0C, Octal 14). 6. Octal Literals (a string of octal characters preceded by & or &O -------------- e.g. &O801 ) Converted to their binary representation, then as for hex literals preceded by a character with ASCII value 11 (decimal) (Hex 0B, Octal 13). 7. Tokens (sustituted for the key words of the language) ------ A complete list of tokens in a C structure follows: struct list { char gw_keyword[10]; char gw_token_hex[3]; char gw_token_octal[3]; }; struct list token_list[]={ "END", "\x81", "\201", "FOR", "\x82", "\202", "NEXT", "\x83", "\203", "DATA", "\x84", "\204", "INPUT", "\x85", "\205", "DIM", "\x86", "\206", "READ", "\x87", "\207", "LET", "\x88", "\210", "GOTO", "\x89", "\211", "RUN", "\x8a", "\212", "IF", "\x8b", "\213", "RESTORE", "\x8c", "\214", "GOSUB", "\x8d", "\215", "RETURN", "\x8e", "\216", "REM", "\x8f", "\217", "STOP", "\x90", "\220", "PRINT", "\x91", "\221", "CLEAR", "\x92", "\222", "LIST", "\x93", "\223", "NEW", "\x94", "\224", "ON", "\x95", "\225", "WAIT", "\x96", "\226", "DEF", "\x97", "\227", "POKE", "\x98", "\230", "CONT", "\x99", "\231", "OUT", "\x9c", "\234", "LPRINT", "\x9d", "\235", "LLIST", "\x9e", "\236", "WIDTH", "\xa0", "\240", "ELSE", ":\xa1", ":\241", "TRON", "\xa2", "\242", "TROFF", "\xa3", "\243", "SWAP", "\xa4", "\244", "ERASE", "\xa5", "\245", "EDIT", "\xa6", "\246", "ERROR", "\xa7", "\247", "RESUME", "\xa8", "\250", "DELETE", "\xa9", "\251", "AUTO", "\xaa", "\252", "RENUM", "\xab", "\253", "DEFSTR", "\xac", "\254", "DEFINT", "\xad", "\255", "DEFSNG", "\xae", "\256", "DEFDBL", "\xaf", "\257", "LINE", "\xb0", "\260", "WHILE", "\xb1\xe9", "\261\351", "WEND", "\xb2", "\262", "CALL", "\xb3", "\263", "WRITE", "\xb7", "\267", "OPTION", "\xb8", "\270", "RANDOMIZE","\xb9", "\271", "OPEN", "\xba", "\272", "CLOSE", "\xbb", "\273", "LOAD", "\xbc", "\274", "MERGE", "\xbd", "\275", "SAVE", "\xbe", "\276", "COLOR", "\xbf", "\277", "CLS", "\xc0", "\300", "MOTOR", "\xc1", "\301", "BSAVE", "\xc2", "\302", "BLOAD", "\xc3", "\303", "SOUND", "\xc4", "\304", "BEEP", "\xc5", "\305", "PSET", "\xc6", "\306", "PRESET", "\xc7", "\307", "SCREEN", "\xc8", "\310", "KEY", "\xc9", "\311", "LOCATE", "\xca", "\312", "TO", "\xcc", "\314", "THEN", "\xcd", "\315", "TAB(", "\xce", "\316", "STEP", "\xcf", "\317", "USR", "\xd0", "\320", "FN", "\xd1", "\321", "NOT", "\xd3", "\323", "ERL", "\xd4", "\324", "ERR", "\xd5", "\325", "STRING$", "\xd6", "\326", "USING", "\xd7", "\327", "INSTR", "\xd8", "\330", "VARPTR", "\xda", "\332", "CSRLIN", "\xdb", "\333", "POINT", "\xdc", "\334", "OFF", "\xdd", "\335", "INKEY$", "\xde", "\336", ">", "\xe6", "\346", "=", "\xe7", "\347", "<", "\xe8", "\350", "+", "\xe9", "\351", "-", "\xea", "\352", "*", "\xeb", "\353", "/", "\xec", "\354", "^", "\xed", "\355", "AND", "\xee", "\356", "OR", "\xef", "\357", "XOR", "\xf0", "\360", "EQV", "\xf1", "\361", "IMP", "\xf2", "\362", "MOD", "\xf3", "\363", "\\", "\xf4", "\364", "CVI", "\xfd\x81", "\375\201", "CVS", "\xfd\x82", "\375\202", "CVD", "\xfd\x83", "\375\203", "MKI$", "\xfd\x84", "\375\204", "MKS$", "\xfd\x85", "\375\205", "MKD$", "\xfd\x86", "\375\206", "FILES", "\xfe\x81", "\376\201", "FIELD", "\xfe\x82", "\376\202", "SYSTEM", "\xfe\x83", "\376\203", "NAME", "\xfe\x84", "\376\204", "LSET", "\xfe\x85", "\376\205", "RSET", "\xfe\x86", "\376\206", "KILL", "\xfe\x87", "\376\207", "PUT", "\xfe\x88", "\376\210", "GET", "\xfe\x89", "\376\211", "RESET", "\xfe\x8a", "\376\212", "COMMON", "\xfe\x8b", "\376\213", "CHAIN", "\xfe\x8c", "\376\214", "DATE$", "\xfe\x8d", "\376\215", "TIME$", "\xfe\x8e", "\376\216", "PAINT", "\xfe\x8f", "\376\217", "COM", "\xfe\x90", "\376\220", "CIRCLE", "\xfe\x91", "\376\221", "DRAW", "\xfe\x92", "\376\222", "PLAY", "\xfe\x93", "\376\223", "TIMER", "\xfe\x94", "\376\224", "ERDEV", "\xfe\x95", "\376\225", "IOCTL", "\xfe\x96", "\376\226", "CHDIR", "\xfe\x97", "\376\227", "MKDIR", "\xfe\x98", "\376\230", "RMDIR", "\xfe\x99", "\376\231", "SHELL", "\xfe\x9a", "\376\232", "ENVIRON", "\xfe\x9b", "\376\233", "VIEW", "\xfe\x9c", "\376\234", "WINDOW", "\xfe\x9d", "\376\235", "PMAP", "\xfe\x9e", "\376\236", "PALETTE", "\xfe\x9f", "\376\237", "LCOPY", "\xfe\xa0", "\376\240", "CALLS", "\xfe\xa1", "\376\241", "PCOPY", "\xfe\xa5", "\376\245", "LOCK", "\xfe\xa7", "\376\247", "UNLOCK", "\xfe\xa8", "\376\250", "LEFT$", "\xff\x81", "\377\201", "RIGHT$", "\xff\x82", "\377\202", "MID$", "\xff\x83", "\377\203", "SGN", "\xff\x84", "\377\204", "INT", "\xff\x85", "\377\205", "ABS", "\xff\x86", "\377\206", "SQR", "\xff\x87", "\377\207", "RND", "\xff\x88", "\377\210", "SIN", "\xff\x89", "\377\211", "LOG", "\xff\x8a", "\377\212", "EXP", "\xff\x8b", "\377\213", "COS", "\xff\x8c", "\377\214", "TAN", "\xff\x8d", "\377\215", "ATN", "\xff\x8e", "\377\216", "FRE", "\xff\x8f", "\377\217", "INP", "\xff\x90", "\377\220", "POS", "\xff\x91", "\377\221", "LEN", "\xff\x92", "\377\222", "STR$", "\xff\x93", "\377\223", "VAL", "\xff\x94", "\377\224", "ASC", "\xff\x95", "\377\225", "CHR$", "\xff\x96", "\377\226", "PEEK", "\xff\x97", "\377\227", "SPACE$", "\xff\x98", "\377\230", "OCT$", "\xff\x99", "\377\231", "HEX$", "\xff\x9a", "\377\232", "LPOS", "\xff\x9b", "\377\233", "CINT", "\xff\x9c", "\377\234", "CSNG", "\xff\x9d", "\377\235", "CDBL", "\xff\x9e", "\377\236", "FIX", "\xff\x9f", "\377\237", "PEN", "\xff\xa0", "\377\240", "STICK", "\xff\xa1", "\377\241", "STRIG", "\xff\xa2", "\377\242", "EOF", "\xff\xa3", "\377\243", "LOC", "\xff\xa4", "\377\244", "LOF", "\xff\xa5", "\377\245", "","",""}; 8. Floating Point Literals (a fractional number e.g. 62.8 ) ----------------------- The most difficult one of the lot! Coded in exponent and mantissa format, preceded by a character with ASCII code 29 (Hex 1D, Octal 35). Consists of four bytes, the first three the mantissa, the last the exponent. The mantissa is held lowest byte first, middle byte second, highest byte third. The mantissa is as would be expected, the successive bits of the floating point number with the highest bit removed (it is always 1). The exponent is the power of two needed in order to shift the number down until it is less than 1, however in the coding the highest bit is inverted. Thus the floating point number 4.5 has an exponent of 3 (or -3 depending on how you look at it) and a mantissa of 1001 (in binary). Hence the coding would be: Hex 00 00 10 83 (Preceded by Hex 1D). I coded this in C as follows: /* If dumnum is the double representation of the number then charexp is the coded exponent and mant2 is the right most byte, mant1 is the middle byte and mant0 is the left most byte of the mantissa. */ /* exponent */ iexp=(int)(log(dumnum)/log(2.0)); /* mantissa in lower three bytes */ imant=(int)(dumnum*pow(2.0,23.0-(double)iexp)); imant=imant&0x007fffff; /* convert to GW-BASIC representation */ iexp++; charexp=iexp^0x80; mant0=(imant>>16)&0xff; mant1=(imant>>8)&0xff; mant2=imant&0xff; I have not investigated what happens for negative numbers, presumably the top bit of the mantissa is set to 1. And note that if dumnum is negative the log(dumnum) will blow up!! That's the lot! Comments, queries, curses, praise to:- Martin Carradus, 3 Connaught Road, Ilkley, West Yorkshire, LS29 8QW. U.K. If you write to me, please enclose an s.a.e. P.S. On an Acorn Archimedes there is the operating system command: *DUMP filename which gives a hex and character dump of the file with the name 'filename'. There is usually a similar command on other computers.