Hello,

Some time ago I wrote an Insertion sort algorithm for Mid-range PICs and=20
today decided to optimize it as much as possible. For this I need to=20
load the negative value of an address of a variable. Using 'movlw  0 -=20
var' or 'addlw 0 - var', where var is a file register is not accepted by=20
MPASM, and 'Error[151] : Operand contains unresolvable labels or is too=20
complex' is issued.

Currently I found 2 workarounds - one needs an extra instruction to=20
convert the loaded address to a negative number, and the other defines=20
an absolute address of 'var' in RAM and then a precalculated negative=20
value of that address is used in the code.

Both of these do not seem right, so I'm searching for a trick to negate=20
the address of 'var' in the preprocessor, without triggering an error.

A part of my code to serve as an example follows.
samp_array	res	N	; an array with N samples to be sorted
ofst			res	1	; Offset in samp_array  =3D current sample address
					; - first sample address
	.
	.

incf	fsr_copy, w
movwf	fsr_copy
movwf	FSR
addlw	0 - samp_array 	; MPASM DOESN'T AGREE WITH THIS EXPRESSION
movwf	ofst				; offset =3D - (first_smp_adrs - cur_smp_adrs)
						; =3D - first_smp_adrs + cur_smp_adrs

This is the first workaround, which adds an extra instruction:
incf		fsr_copy, w
movwf	fsr_copy
movwf	FSR			; At this point W holds the address of the current sample
					; Now an offset from the beginning of samp_array must be
					; calculated and then stored in ofst.
sublw	samp_array	; Calculate the offset (first sample address -
					; current sample addres).
					; The result is a negative number.
clrf		ofst			; AN EXTRA INSTRUCTION IS ADDED
subwf	ofst, f		; (0 - offset) the offset is now positive.


I'd gladly share the complete Insertion sort code, if anyone is interested.

Regards,
Svetlin
--=20
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