/* Non-restoring dvision algorithm according to
   http://www.arpnjournals.org/jeas/research_papers/rp_2017/jeas_0517_6036.pdf */

module divi_comb #(parameter NBITS_DEND=8, // number of bits of dividend
                             NBITS_SOR=8,  // number of bits of divisor
                             NBITS_Q=8)    // number of bits of quotient
            (input logic  [NBITS_DEND-1:0] dend, // dividend
             input logic  [NBITS_SOR -1:0] sor,  // divisor
             output logic [NBITS_Q   -1:0] q);   // quotient

// for vcs (Synopsys simulator) change <= to = in lines 26,27,29

/* verilator lint_off UNOPTFLAT */

  // remainders, one for each quotient bit plus one for initialization
  logic [NBITS_SOR-1:0] rem [NBITS_Q+1:1];
  logic [NBITS_SOR:0] rems [NBITS_Q+1:0]; // shifted remainder

  always_comb // inverted most significant bits of remainders are the quotient
    for(int i=1; i<=NBITS_Q; i++)
      q[NBITS_Q-i] <= ~rem[i+1][NBITS_SOR-1];

  always_comb begin
    rems[0] <= 0;  // initial shifted remainder
    for(int i=0; i<=NBITS_Q; i++) begin // calculate all remainders
      // if remainder is negative, add else subtract divisor
      if(rems[i][NBITS_SOR]) rem[i+1] <= rems[i] + sor;
      else                   rem[i+1] <= rems[i] - sor;
      // shift in the next didivend bit
      rems[i+1] <= { rem[i+1], i<NBITS_DEND ? dend[NBITS_DEND-1-i] : 1'b0 };
    end
  end

/* verilator lint_on UNOPTFLAT */
endmodule