src/add/fsqrt.py

   1 def sqrt(num):
   2
   3     res = 0
   4     bit = 1 << 14
   5
   6     while (bit > num):
   7         bit >>= 2
   8
   9     while (bit != 0):
  10         if (num >= res + bit):
  11             num -= res + bit
  12             res = (res >> 1) + bit
  13         else:
  14             res >>= 1
  15         bit >>= 2
  16
  17     return res
  18
  19 """
  20 //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
  21 //
  22
  23 module testbench;
  24
  25 reg [15:0] sqr;
  26
  27 //Verilog function to find square root of a 32 bit number.
  28 //The output is 16 bit.
  29 function [15:0] sqrt;
  30     input [31:0] num;  //declare input
  31     //intermediate signals.
  32     reg [31:0] a;
  33     reg [15:0] q;
  34     reg [17:0] left,right,r;
  35     integer i;
  36 begin
  37     //initialize all the variables.
  38     a = num;
  39     q = 0;
  40     i = 0;
  41     left = 0;   //input to adder/sub
  42     right = 0;  //input to adder/sub
  43     r = 0;  //remainder
  44     //run the calculations for 16 iterations.
  45     for(i=0;i<16;i=i+1) begin
  46         right = {q,r[17],1'b1};
  47         left = {r[15:0],a[31:30]};
  48         a = {a[29:0],2'b00};    //left shift by 2 bits.
  49         if (r[17] == 1) //add if r is negative
  50             r = left + right;
  51         else    //subtract if r is positive
  52             r = left - right;
  53         q = {q[14:0],!r[17]};
  54     end
  55     sqrt = q;   //final assignment of output.
  56 end
  57 endfunction //end of Function
  58
  59
  60 c version (from paper linked from URL)
  61
  62 unsigned squart(D, r) /*Non-Restoring sqrt*/
  63     unsigned D; /*D:32-bit unsigned integer to be square rooted */
  64     int *r;
  65 {
  66     unsigned Q = 0; /*Q:16-bit unsigned integer (root)*/
  67     int R = 0; /*R:17-bit integer (remainder)*/
  68     int i;
  69     for (i = 15;i>=0;i--) /*for each root bit*/
  70     {
  71         if (R>=0)
  72         { /*new remainder:*/
  73             R = R<<2)|((D>>(i+i))&3);
  74             R = R-((Q<<2)|1); /*-Q01*/
  75         }
  76         else
  77         { /*new remainder:*/
  78             R = R<<2)|((D>>(i+i))&3);
  79             R = R+((Q<<2)|3); /*+Q11*/
  80         }
  81         if (R>=0) Q = Q<<1)|1; /*new Q:*/
  82         else Q = Q<<1)|0; /*new Q:*/
  83     }
  84
  85     /*remainder adjusting*/
  86     if (R<0) R = R+((Q<<1)|1);
  87     *r = R; /*return remainder*/
  88     return(Q); /*return root*/
  89 }
  90
  91 From wikipedia page:
  92
  93 short isqrt(short num) {
  94     short res = 0;
  95     short bit = 1 << 14; // The second-to-top bit is set: 1 << 30 for 32 bits
  96
  97     // "bit" starts at the highest power of four <= the argument.
  98     while (bit > num)
  99         bit >>= 2;
 100
 101     while (bit != 0) {
 102         if (num >= res + bit) {
 103             num -= res + bit;
 104             res = (res >> 1) + bit;
 105         }
 106         else
 107             res >>= 1;
 108         bit >>= 2;
 109     }
 110     return res;
 111 }
 112
 113 """