Fill Routine

[boriel]

I'm puzzled.
The __DECY routine and the one in our code *differ* hock:
I now remember where did I took these routines from this Speccy Tutorial

Code:

__DECY: SPPixelDown: * dec b inc h inc h ld a,h ld a, h and $07 and 7 ret nz ret nz ld a,h * ex af, af' sub $08 * scf ld h,a * ex af, af' ld a,l ld a, l add a,$20 add a, 32 ld l,a ld l, a ret nc ret c ld a,h ld a, h add a,$08 sub 8 ld h,a ld h, a cp $58 ret ccf ret

The dec b, and ex af, af' sequence on the left (marked with an asterisk *) can be ignored. But the SP routine on the right does an extra ADD a, 08 mine does not do :?:
Accoding to Speccy.org seems to be an optimization. Any ideas?