lda link_buffer
    sta zp_tmp1
    lda link_buffer+1
    sta zp_tmp1+1
    ldy #3
    lda link_content
    sta (zp_tmp1),y
    iny
    lda link_content+1
    sta (zp_tmp1),y


    ;translate to origin -> signed numbers!
    lda pxpos
    sec
    sbc #80
    sta tmp1
    bpl ispositive0
isnegative0
    clc
    eor #$ff
    adc #$01
ispositive0
;------------------------
    and #7
    asl
    asl
    asl
    asl
    asl
    sta rem1

    lda tmp1 ;now re-attach the sign?
    bpl waspositive0
wasnegative0
    lda rem1
    clc
    eor #$ff
    adc #$01
    sta rem1
waspositive0
;------------------------
;------------------------
    lda pypos
    sec
    sbc #20
    sta tmp2
;------------------------
    ;tmp2 can be negative
    ;so check first
    bpl ispositive
isnegative
    clc
    eor #$ff
    adc #$01

ispositive
    and #3
    asl
    asl
    asl
    asl
    asl
    asl
    sta rem2

    lda tmp2 ;now re-attach the sign?
    bpl waspositive
wasnegative
    lda rem2
    clc
    eor #$ff
    adc #$01
    sta rem2
waspositive
;------------------------


    lda rem1
    clc
    adc rem2
    lda #0
    adc #0
    sta rem_msb1


    ;pxpos / 8
    lda tmp1 ;
    cmp #$80  ;copy bit 7 to carry
    ror       ;shift right as before
    bpl *+4     ;if positive number then skip
    adc #$00  ;else round up
    sta tmp1

    lda tmp1 ;
    cmp #$80  ;copy bit 7 to carry
    ror       ;shift right as before
    bpl *+4     ;if positive number then skip
    adc #$00  ;else round up
    sta tmp1

    lda tmp1 ;
    cmp #$80  ;copy bit 7 to carry
    ror       ;shift right as before
    bpl *+4     ;if positive number then skip
    adc #$00  ;else round up
    sta tmp1

   ;pypos / 4
    lda tmp2 ;
    cmp #$80  ;copy bit 7 to carry
    ror       ;shift right as before
    bpl *+4     ;if positive number then skip
    adc #$00  ;else round up
    sta tmp2

    lda tmp2 ;
    cmp #$80  ;copy bit 7 to carry
    ror       ;shift right as before
    bpl *+4     ;if positive number then skip
    adc #$00  ;else round up
    sta tmp2

    ;tmp3=tmp1+tmp2 + ((rem1+rem2)>>8)
    lda tmp1
    clc
    adc tmp2
    adc rem_msb1
    sta tmp3


    lda tmp3 ;
    cmp #$80  ;copy bit 7 to carry
    ror       ;shift right as before
    bpl *+4     ;if positive number then skip
    adc #$00  ;else round up
    sta tmp3
    ;tmp3 = map.x = (screen.x / TILE_WIDTH_HALF + screen.y / TILE_HEIGHT_HALF) /2;


    ;tmp4=tmp2-tmp1 + ((rem2-rem1)>>8)
    lda rem2
    sec
    sbc rem1
    lda #0
    sbc #0
    sta rem_msb2

#ifdef DEBUG
    lda rem1
    ldx #10
    ldy #10
    jsr plot_a_xy

    lda rem2
    ldx #30
    ldy #10
    jsr plot_a_xy

    lda rem_msb1
    ldx #50
    ldy #10
    jsr plot_a_xy

    lda rem_msb2
    ldx #70
    ldy #10
    jsr plot_a_xy
#endif


    lda tmp2
    sec
    sbc tmp1
    clc
    adc rem_msb2
    sta tmp4

    lda tmp4 ;
    cmp #$80  ;copy bit 7 to carry
    ror       ;shift right as before
    bpl *+4     ;if positive number then skip
    adc #$00  ;else round up
    sta tmp4
    ;tmp4= map.y = (screen.y / TILE_HEIGHT_HALF -(screen.x / TILE_WIDTH_HALF)) /2;


#ifdef DEBUG
    lda tmp3
    ldx #10
    ldy #90
    jsr plot_a_xy

    lda tmp4
    ldx #24
    ldy #90
    jsr plot_a_xy
#endif
    lda tmp4
    sta     MATHD   ; Hardware multiply
    stz     MATHC

    lda #10
    sta     MATHB   ; Hardware multiply
    stz     MATHA

    bit $fc92;SPRSYS
    bmi *-3

    lda tmp3
    clc
    adc MATHH ;y*10

    sta player_map_pos
#ifdef DEBUG
    ldx #50
    ldy #90
    jsr plot_a_xy
#endif
    ;debug screeny
    ;just for debug
;------
#ifdef DEBUG
    lda #0
    sta count
loop2
    ldx count
    lda omappos,x
    pha;
    ldy #80
    lda count
    asl
    asl
    asl
    asl
    tax
    pla ;
    jsr plot_a_xy
    inc count
    lda count
    cmp #10
    bne loop2
;------
#endif
    ;inject player;
    lda #0
    sta count
loop3
    ldx count
    lda omappos,x
    cmp player_map_pos
    bcs inject_here
    inc count
    lda count
    cmp #10
    bne loop3
    ;rts
inject_here
    ;x*11
    lda #<(object_chain)
    sta zp_tmp1
    lda #>(object_chain)
    sta zp_tmp1+1

   ; ldx #5
    stx player_position_in_list

    cpx #0
    beq skip_search
    dex ;WHY? TRY TO UNDERSTAND BUG NOTE TODO
loop4 ;go through object chain in steps of OFFSET = 11
    lda zp_tmp1
    clc
    adc #11
    sta zp_tmp1
    bcc ok
    inc zp_tmp2
ok
    dex
    bne loop4

skip_search
#ifdef DEBUG
    lda player_position_in_list
    ldx #10
    ldy #30
    jsr plot_a_xy
#endif
    ;backup chain link
    lda zp_tmp1
    sta link_buffer
    lda zp_tmp1+1
    sta link_buffer+1
    ldy #3
    lda (zp_tmp1),y
    sta link_content
    iny
    lda (zp_tmp1),y
    sta link_content+1

    ;zp_tmp1 points to sprite to exchange
    ldy #3
    lda (zp_tmp1),y
    sta player_chain ;point player to next chain link
    lda #<player ;insert player into chain
    sta (zp_tmp1),y

    iny
    lda (zp_tmp1),y
    sta player_chain+1
    lda #>player ;insert player into chain
    sta (zp_tmp1),y
    rts

link_buffer .word object_chain
link_content .word object_chain+11
player_position_in_list .byte 0
player_map_pos .byte 0
count .byte 0
mapxp .byte 0
mapyp .byte 0
tmp1 .byte 0
tmp2 .byte 0
tmp3 .byte 0
tmp4 .byte 0

rem1 .byte 0
rem2 .byte 0
rem_msb1 .byte 0
rem_msb2 .byte 0
.)