Yeah, mine is lossy, but its very compact and tiny. The most I have seen it off is by 4 binary degrees but on average its usually less than 3. It is exact every 45 degrees. This is the routine I'm using:
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| p_ArcTan:
.db __ArcTanEnd-1-$
ex de,hl ;de = y
pop hl
ex (sp),hl ;hl = x
push hl
ld a,h ;\
xor d ; |Get pairity
rla ;/
jr c,__ArcTanSS ;\
add hl,de ; |
add hl,de ; |
__ArcTanSS: ; |
or a ; |hl = x +- y
sbc hl,de ;/
ex de,hl ;de = x +- y
ld b,6 ;\
__ArcTan64: ; |
add hl,hl ; |hl = 64y
djnz __ArcTan64 ;/
call $3F00+sub_SDiv ;hl = 64y/(x +- y)
pop af ;\
rla ; |Right side, fine
ret nc ;/
sbc a,a ;\
sub h ; |Reverse sign extend
ld h,a ;/
ld a,l ;\
add a,128 ; |Add or sub 128
ld l,a ;/
ret
__ArcTanEnd:
|
The arguments are currently backwards; (X,Y) instead of the traditional (Y,X). I'm not sure which one I'm going to use yet.
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