DOS commands with "L" parameter and range 1 to 32767

[TommyGH]

This isn't really an issue as much as an observation that can be easily overlooked.

OPTAB3

2963:FF 7F DW 32767 ; LENGTH RANGE

You might already be aware of this, but having this defined as a range 1 to 32767 for the L parameter, when you start at an even page boundary you will not get the last byte in the last page of memory that you might think you did.

To really save exactly 32K memory, the range would need to be 1 to 32768. Of course 32768 is 1 greater than "max int".

As examples:

~BSAVE BIG,A$800,L$32767~ BSAVE BIG,A$800,L32767 BSAVE BIG,A$800,L$7FFF

These examples save memory from $0800 through $87FE (and not $87FF).

As a thought experiment, how would you ever designate you wanted to save all 64K of memory even with changing the value in OPTAB3 to 65535 (FF FF)?

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[ Note: I edited this message to fix the first example. --Michael]

[Michaelangel007]

Thanks for the insight Tommy! I didn't realize there was an overflow / off-by-one bug lurking there.

Interesting "puzzle". Simple solution would be to use 3-bytes and fix the parser. If we are restricted to $FFFF then there are two conditions we need to check:

• zero
• over-flow

Specifically,

• BSAVE ZERO,A$0,L$0
• BSAVE BIG, A$0,L$10000

[Michaelangel007]

Context / Reference:

2138:D9 55 29       221             CMP OPTAB3,Y    ; WITH LOW RANGE (LOW)          ; +0 = OptValMin[x].Lo ?
213F:D9 58 29       224 SP5         CMP OPTAB3+3,Y                                  ; +3 = OptValMax[x].Hi ?
2148:D9 57 29       228             CMP OPTAB3+2,Y                                  ; +2 = OptValMax[x].Lo