dasm special-cases negative immediates in, for example...
VAL = -1
lda #VAL. ; assembles OK
Although numbers are stored internally as 32 bits, and by rights this would be equivalent to...
... it assembles OK with dasm using the low bye ($FF) of the internal 32-byte number.
All good so far. It's detecting that the two's complement negative can be expressed as a single byte.
However, long ago when I was "fixing" things, and as a result we were required to write ...
VAL = -1
lda #VAL&$FF. ; nobody liked this
... well the "fix" was reverted/fixed, and we could once again write just ``lda #-1"
The rationale being that dasm would range-check (I am guessing) to detect if the operand was in the correct (signed or unsigned) range. And now to my point...
The valid signed range is of course 8 bits (2's complement). That is from $80 (-128 signed) to $FF (unsigned).
We should be able to use any value in that range without error. But not outside it.
It seems, however, that dasm is restricting the range to -$FF to +$FF, which is incorrect.
The correct range, as noted, is -$80 to +$FF.
As an example, the following assembles - and it should not...
lda #-130. ; whoops! Range should be -128 to 255 inclusive.
dasm special-cases negative immediates in, for example...
Although numbers are stored internally as 32 bits, and by rights this would be equivalent to...
... it assembles OK with dasm using the low bye ($FF) of the internal 32-byte number.
All good so far. It's detecting that the two's complement negative can be expressed as a single byte.
However, long ago when I was "fixing" things, and as a result we were required to write ...
... well the "fix" was reverted/fixed, and we could once again write just ``lda #-1"
The rationale being that dasm would range-check (I am guessing) to detect if the operand was in the correct (signed or unsigned) range. And now to my point...
The valid signed range is of course 8 bits (2's complement). That is from $80 (-128 signed) to $FF (unsigned).
We should be able to use any value in that range without error. But not outside it.
It seems, however, that dasm is restricting the range to -$FF to +$FF, which is incorrect.
The correct range, as noted, is -$80 to +$FF.
As an example, the following assembles - and it should not...