DMG Fading functions allows to fade in/out to black and in/out to white

gistfile1.txt

UBYTE DMGFadetoWhiteStep(UBYTE pal, UBYTE step) __naked {
    pal; step;
__asm
            lda     HL, 3(SP)
            ld      A, (HL-)
            ld      E, (HL)
            or      A
            ret     Z
            
            ld      D, A
1$: 
            ld      H, #4
2$:
            ld      A, E
            and     #3
            jr      Z, 3$
            dec     A         
3$:
            srl     A
            rr      L
            srl     A
            rr      L
            
            srl     E
            srl     E

            dec     H
            jr      NZ, 2$

            ld      E, L

            dec     D
            jr      NZ, 1$
            ret   
__endasm;
}

UBYTE DMGFadeToBlackStep(UBYTE pal, UBYTE step) __naked {
    pal; step;
__asm
            lda     HL, 3(SP)
            ld      A, (HL-)
            ld      E, (HL)
            or      A
            ret     Z
            
            ld      D, A
1$: 
            ld      H, #4
2$:
            ld      A, E
            and     #3
            cp      #3
            jr      Z, 3$
            inc     A         
3$:
            srl     A
            rr      L
            srl     A
            rr      L
            
            srl     E
            srl     E

            dec     H
            jr      NZ, 2$

            ld      E, L

            dec     D
            jr      NZ, 1$
            ret   
__endasm;
}