calDmg = (((((((wpn->strMin << 8) + ((randStr * ((wpn->strMax - wpn->strMin) << 8)) >> 8)) * (strength / defense)) >> 8) * i) >> 8) * calWpnDmg) >> 8;

полученный урон = мин. урон оружия + (((случайный урон оружия)*атака)*(атака/защита врага))
смещаем результат на 4 бита вправо (делим на 4) и прибавляем 1 (для того, чтобы даже при очень большом разрыве прилетал урон в 1 пункт)
если для врага оружие смертельно, то смещаем биты на 2 влево (умножаем на 2)

        ; ---------------------- CALCULATE DAMAGE ------------------------------
        ; weapon_min + (rand(weapon_min; weapon_max) * ((((player_attack << 4)/enemy_defence)*32)>>6))
        ; ----------------------------------------------------------------------
        ; rotate left player attack 4 times
        lda     fight_player_attack
        sta     rotate_inout
        lda     #0
        sta     rotate_inout+1
        ldy     #3
        jsr     rol_16bit
        ; divide player_attack by enemy_defence
        lda     rotate_inout 
        sta     div_dividend
        lda     rotate_inout+1
        sta     div_dividend+1
        lda     fight_enemy_defence
        sta     div_divisor
        lda     #0
        sta     div_divisor+1
        jsr     divide_16bit
        ; multiply the previous result by 32
        lda     div_dividend
        sta     mult_f_number
        lda     div_dividend+1
        sta     mult_f_number+1
        lda     #32
        sta     mult_s_number
        lda     #0
        sta     mult_s_number+1
        jsr     mult_16bit
        ; rotate right the previous result 6 times
        lda     mult_result
        sta     rotate_inout
        lda     mult_result+1
        sta     rotate_inout+1
        ldy     #5
        jsr     ror_16bit
        ; get random weapon strength
        jsr     get_random_number
        lda     rnd_1
        ldy     curr_weapon_mod
        jsr     mod
        clc
        adc     curr_weapon_add
        ; multiply random number by the previous result
        sta     mult_f_number
        lda     #0
        sta     mult_f_number+1
        lda     rotate_inout
        sta     mult_s_number
        lda     rotate_inout+1
        sta     mult_s_number+1
        jsr     mult_16bit
        ; add minimum weapon strength
        lda     mult_result
        clc
        adc     curr_weapon_add
        sta     mult_result
        lda     mult_result+1
        adc     #0
        sta     mult_result+1