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
  14         else:
  15             res >>= 1;
  16         bit >>= 2;
  17
  18     return res
  19
  20 """
  21 //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
  22 //
  23
  24 module testbench;
  25
  26 reg [15:0] sqr;
  27
  28 //Verilog function to find square root of a 32 bit number.
  29 //The output is 16 bit.
  30 function [15:0] sqrt;
  31     input [31:0] num;  //declare input
  32     //intermediate signals.
  33     reg [31:0] a;
  34     reg [15:0] q;
  35     reg [17:0] left,right,r;
  36     integer i;
  37 begin
  38     //initialize all the variables.
  39     a = num;
  40     q = 0;
  41     i = 0;
  42     left = 0;   //input to adder/sub
  43     right = 0;  //input to adder/sub
  44     r = 0;  //remainder
  45     //run the calculations for 16 iterations.
  46     for(i=0;i<16;i=i+1) begin
  47         right = {q,r[17],1'b1};
  48         left = {r[15:0],a[31:30]};
  49         a = {a[29:0],2'b00};    //left shift by 2 bits.
  50         if (r[17] == 1) //add if r is negative
  51             r = left + right;
  52         else    //subtract if r is positive
  53             r = left - right;
  54         q = {q[14:0],!r[17]};
  55     end
  56     sqrt = q;   //final assignment of output.
  57 end
  58 endfunction //end of Function
  59
  60
  61 c version (from paper linked from URL)
  62
  63 unsigned squart(D, r) /*Non-Restoring sqrt*/
  64     unsigned D; /*D:32-bit unsigned integer to be square rooted */
  65     int *r;
  66 {
  67     unsigned Q = 0; /*Q:16-bit unsigned integer (root)*/
  68     int R = 0; /*R:17-bit integer (remainder)*/
  69     int i;
  70     for (i = 15;i>=0;i--) /*for each root bit*/
  71     {
  72         if (R>=0)
  73         { /*new remainder:*/
  74             R = R<<2)|((D>>(i+i))&3);
  75             R = R-((Q<<2)|1); /*-Q01*/
  76         }
  77         else
  78         { /*new remainder:*/
  79             R = R<<2)|((D>>(i+i))&3);
  80             R = R+((Q<<2)|3); /*+Q11*/
  81         }
  82         if (R>=0) Q = Q<<1)|1; /*new Q:*/
  83         else Q = Q<<1)|0; /*new Q:*/
  84     }
  85
  86     /*remainder adjusting*/
  87     if (R<0) R = R+((Q<<1)|1);
  88     *r = R; /*return remainder*/
  89     return(Q); /*return root*/
  90 }
  91
  92 From wikipedia page:
  93
  94 short isqrt(short num) {
  95     short res = 0;
  96     short bit = 1 << 14; // The second-to-top bit is set: 1 << 30 for 32 bits
  97
  98     // "bit" starts at the highest power of four <= the argument.
  99     while (bit > num)
 100         bit >>= 2;
 101
 102     while (bit != 0) {
 103         if (num >= res + bit) {
 104             num -= res + bit;
 105             res = (res >> 1) + bit;
 106         }
 107         else
 108             res >>= 1;
 109         bit >>= 2;
 110     }
 111     return res;
 112 }
 113
 114 """