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

[exodustx0]

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.)

[exodustx0]

Tangential note: for both Asar 1.91 and 2.0, bra and the simple conditional branches write the opcode and branch offset before checking the offset's correctness, and the bit check conditional branches (bbc and bbs), as well as my above workaround macro, write just the opcode before checking offset correctness. dbnz and cbne, in my opinion correctly, check offset correctness before writing anything.