src/add/fsqrt.py

   1
   2
   3 """
   4 //This is the main code of integer sqrt function found here:http://verilogcodes.blogspot.com/2017/11/a-verilog-function-for-finding-square-root.html
   5 //
   6
   7 module testbench;
   8
   9 reg [15:0] sqr;
  10
  11 //Verilog function to find square root of a 32 bit number.
  12 //The output is 16 bit.
  13 function [15:0] sqrt;
  14     input [31:0] num;  //declare input
  15     //intermediate signals.
  16     reg [31:0] a;
  17     reg [15:0] q;
  18     reg [17:0] left,right,r;
  19     integer i;
  20 begin
  21     //initialize all the variables.
  22     a = num;
  23     q = 0;
  24     i = 0;
  25     left = 0;   //input to adder/sub
  26     right = 0;  //input to adder/sub
  27     r = 0;  //remainder
  28     //run the calculations for 16 iterations.
  29     for(i=0;i<16;i=i+1) begin
  30         right = {q,r[17],1'b1};
  31         left = {r[15:0],a[31:30]};
  32         a = {a[29:0],2'b00};    //left shift by 2 bits.
  33         if (r[17] == 1) //add if r is negative
  34             r = left + right;
  35         else    //subtract if r is positive
  36             r = left - right;
  37         q = {q[14:0],!r[17]};
  38     end
  39     sqrt = q;   //final assignment of output.
  40 end
  41 endfunction //end of Function
  42
  43
  44 c version (from paper linked from URL)
  45
  46 unsigned squart(D, r) /*Non-Restoring sqrt*/
  47     unsigned D; /*D:32-bit unsigned integer to be square rooted */
  48     int *r;
  49 {
  50     unsigned Q = 0; /*Q:16-bit unsigned integer (root)*/
  51     int R = 0; /*R:17-bit integer (remainder)*/
  52     int i;
  53     for (i = 15;i>=0;i--) /*for each root bit*/
  54     {
  55         if (R>=0)
  56         { /*new remainder:*/
  57             R = R<<2)|((D>>(i+i))&3);
  58             R = R-((Q<<2)|1); /*-Q01*/
  59         }
  60         else
  61         { /*new remainder:*/
  62             R = R<<2)|((D>>(i+i))&3);
  63             R = R+((Q<<2)|3); /*+Q11*/
  64         }
  65         if (R>=0) Q = Q<<1)|1; /*new Q:*/
  66         else Q = Q<<1)|0; /*new Q:*/
  67     }
  68
  69     /*remainder adjusting*/
  70     if (R<0) R = R+((Q<<1)|1);
  71     *r = R; /*return remainder*/
  72     return(Q); /*return root*/
  73 }
  74
  75 From wikipedia page:
  76
  77 short isqrt(short num) {
  78     short res = 0;
  79     short bit = 1 << 14; // The second-to-top bit is set: 1 << 30 for 32 bits
  80
  81     // "bit" starts at the highest power of four <= the argument.
  82     while (bit > num)
  83         bit >>= 2;
  84
  85     while (bit != 0) {
  86         if (num >= res + bit) {
  87             num -= res + bit;
  88             res = (res >> 1) + bit;
  89         }
  90         else
  91             res >>= 1;
  92         bit >>= 2;
  93     }
  94     return res;
  95 }
  96
  97 """