SPC700 branch instructions don't support over-/underflowing PC

[exodustx0]

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arch spc700
norom
org $0000

base $0000
foo: bra bar

base $FFF0
bar: bra foo

This prints two Erelative_branch_out_of_bounds errors, for values 65518 and -65522 respectively. The S-SMP, however, supports over- and underflowing of the PC, i.e. I expect an output of 2F EE 2F 0E. Note that this behaviour is also present for all conditional branches, including dbnz, cbne, bbc and bbs.

I have not tested Asar 2.0, but a quick look through the code suggests that the behaviour is the same there.

I've written a workaround macro in the meantime:

MACRO	RelativeAddressOffsetByte(dst)
	!__dst	= ((<dst>)-(pc()+1))
	!__x	= (!__dst+(less(!__dst, -$80)*$10000)-(greaterequal(!__dst, $80)*$10000))

	ASSERT	!__x >= -$80 && !__x < $80, "Label out of range for branch."
	DB		!__x&$FF
	UNDEF	"__x"
	UNDEF	"__dst"
ENDMACRO

MACRO	BRA(dst)
	DB		$2F
	%		RelativeAddressOffsetByte(<dst>)
ENDMACRO

MACRO	CBNE(check, dst)
	ASSERT	<check>&~$FF == 0

	DB		$2E
	DB		<check>
	%		RelativeAddressOffsetByte(<dst>)
ENDMACRO

; etc...

(less and greaterequal instead of if because of non-static labels.)