RSTS/E .BAC file format


Conventions: SP = stack pointer
addresses are actually address/2-256

Byte(s)			Description
-------			-----------
0-1			Checksum (add words 1-end).  This is word 0.
2-3			Corresponds to memory position 514.
SP+1			Internal version # (upper byte).
			RSTS/E revision level (lower byte)
SP+2			RSTS/E vesion level (CVT%$ format)
SP+4			CSR area pointer
SP+6			Count of saved CSR's pointer (CSCSR)
SP+8			Pointer to saved CSRs (each CSR is 2 words)
SP+8+(CSCSR*2)		Math package description (upper byte)
			if < 128, then 4-word.  If >127, negate and that is the
			scale factor (word size is upper byte).
SP+28			Data area pointer (SPDA)
SP+30			Text area pointer (SPTA)
SP+38			Math package (2 or 4)
SP+39			Scale factor.  Take 256-(@(SP+39)), AND it with 255.
			Then get 10^value.
SPDA+1214		Start of variable table
SPDA+1152		STATUS
SPDA+1156		ERL
SPDA+1160		RECOUNT
SPDA+1180		NUM2
SPDA+1184		NUM
SPDA+1188		ERR
SPDA+1190		DET
SPDA+1198		PI
SPDA+@SPDA		Header to line 0 address

The variable table is 26 entries long (1 for each letter).  Each entry is a
word position.  0 means no variables by that name.  Otherwise, add value to
SPDA+1214+entry number (0-23).  Variable is stored backwards, byte-wise, from
that address (-1) until you find a bye value > 127.  That value is a flag with
the following meanings (bit 128 is always set):	AND 1 = integer
						AND 2 = floating
						AND 4 = string
						AND 8 = array
						AND 16 = function
Note that if the variable type flag is on an odd byte, then the previous (even)
byte is also that variable flag.
For instance, if you had a variable "EXIT", you would look at the "E" entry
in the table, take that pointer and search backwards for "XIT".
After the variable type are the following:

size (words)	Description
------------	-----------
1		Pointer to next type with same name (offset from this address)
1		Second permanent dimension if array.  Value for integer.  Top
		wrod of floating.  Link for string.
1		First permanent dimension if array.  Pointer for string.
1		Length if string.  String size / 2 if virtual.
3		?
1		Channel number * 2 (if virtual)


Run-time environment

Address			Meaning
-------			-------
16-39			Last open file
	16		(upper byte) = MSB of file size (or else 377)
	18		PPN
	20-24		Name
	26		LSW of file size
	28		Buffersize
	30		Mode
	32		Status
	34		clustersize (0 means 256)
	35		Protection code
	36		Device name
	38		Unit # & flags
46			Pointer to break flags (if <0 then break on all lines)
122			Break line 1
124			Break line 2
.
.
.
140			Break line 16
440			SCTH
442			SPTA
444			SPDA
446			Pointer to bottom (top) of SP stack

#SP+40			Top (bottom) of traceback info.  If = @446, then end of
			traceback information.
@(SP+40)		Return address for first block
@(SP+42)		Offset from SPTA for header pointer
@(SP+46)		>0 if function rather than SUB, and next 4 words are
			context info
@(@(SP+42)+10)		Line number

Editor flag word:
	AND 16 = Check bit 32
	AND 32 = Not compiled
	AND 128 = CONTinue allowed
	AND 2048 = EXTEND mode
	AND 8192 = default is EXTEND mode
Key:
	AND 1 = BREAK enabled
	AND 8 = TRACE enabled

To find contents of string, take pointer value and add link.


Arrays:

Take location of variable type - 28 as the base address
Offset	Description
------	-----------
0	Link (add thsi value to memory pointed to by pointer)
2	Pointer to data (offset)
4	True if referenced
6	First current dimension
8	Second current dimension
10	I/O channel * 2 (0 if none)
22	Second permanent dimension
24	First permanent dimension


I/O Channels:

Address		Description
-------		-----------
@(SPDA+44+16)	IOCHAN
@(IOCHAN+x*16)	IOINFO
@IOINFO+2	0 if not open, otherwise offset from IOCHAN
@IOINFO+4	Buffersize
@IOINFO+6	Bytes in buffer
@IOINFO+10	CHannel # * 2 (lower byte)
@IOINFO+12	MSB of filesize (high byte)
		CCPOS (low byte)
@IOINFO+14	LSW of filesize

@(IOINFO+8)-@(IOINFO+2) is current pointer