src/add/fsqrt.py

   1 # XXX DO NOT USE, fails on num=65536.  wark-wark...
   2 def sqrtsimple(num):
   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 def sqrt(num):
  21     D = num # D is input (from num)
  22     Q = 0
  23     R = 0
  24     r = 0 # remainder
  25     for i in range(15, -1, -1): # negative ranges are weird...
  26
  27         if (R>=0):
  28
  29             R = (R<<2)|((D>>(i+i))&3)
  30             R = R-((Q<<2)|1) #/*-Q01*/
  31
  32         else:
  33
  34             R = (R<<2)|((D>>(i+i))&3)
  35             R = R+((Q<<2)|3) #/*+Q11*/
  36
  37         if (R>=0):
  38             Q = (Q<<1)|1 #/*new Q:*/
  39         else:
  40             Q = (Q<<1)|0 #/*new Q:*/
  41
  42
  43     if (R<0):
  44         R = R+((Q<<1)|1)
  45         r = R
  46     return Q
  47
  48
  49 # grabbed these from unit_test_single (convenience, this is just experimenting)
  50
  51 def get_mantissa(x):
  52     return 0x7fffff & x
  53
  54 def get_exponent(x):
  55     return ((x & 0x7f800000) >> 23) - 127
  56
  57 def set_exponent(x, e):
  58     return (x & ~0x7f800000) | ((e+127) << 23)
  59
  60 def get_sign(x):
  61     return ((x & 0x80000000) >> 31)
  62
  63 # convert FP32 to s/e/m
  64 def create_fp32(s, e, m):
  65     """ receive sign, exponent, mantissa, return FP32 """
  66     return set_exponent((s << 31) | get_mantissa(m))
  67
  68 # convert s/e/m to FP32
  69 def decode_fp32(x):
  70     """ receive FP32, return sign, exponent, mantissa """
  71     return get_sign(x), get_exponent(x), get_mantissa(x)
  72
  73
  74 # main function, takes mantissa and exponent as separate arguments
  75 # returns a tuple, sqrt'd mantissa, sqrt'd exponent
  76
  77 def main(mantissa, exponent):
  78     if exponent & 1 != 0:
  79         return sqrt(mantissa << 1), # shift mantissa up
  80                 ((exponent - 1) / 2) # subtract 1 from exp to compensate
  81     return sqrt(mantissa),      # mantissa as-is
  82            (exponent / 2)       # no compensating needed on exp
  83
  84
  85 if __name__ == '__main__':
  86     for Q in range(1, int(1e7)):
  87         print(Q, sqrt(Q), sqrtsimple(Q), int(Q**0.5))
  88         assert int(Q**0.5) == sqrtsimple(Q), "Q sqrtsimpl fail %d" % Q
  89         assert int(Q**0.5) == sqrt(Q), "Q sqrt fail %d" % Q
  90
  91 """
  92 //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
  93 //
  94
  95 module testbench;
  96
  97 reg [15:0] sqr;
  98
  99 //Verilog function to find square root of a 32 bit number.
 100 //The output is 16 bit.
 101 function [15:0] sqrt;
 102     input [31:0] num;  //declare input
 103     //intermediate signals.
 104     reg [31:0] a;
 105     reg [15:0] q;
 106     reg [17:0] left,right,r;
 107     integer i;
 108 begin
 109     //initialize all the variables.
 110     a = num;
 111     q = 0;
 112     i = 0;
 113     left = 0;   //input to adder/sub
 114     right = 0;  //input to adder/sub
 115     r = 0;  //remainder
 116     //run the calculations for 16 iterations.
 117     for(i=0;i<16;i=i+1) begin
 118         right = {q,r[17],1'b1};
 119         left = {r[15:0],a[31:30]};
 120         a = {a[29:0],2'b00};    //left shift by 2 bits.
 121         if (r[17] == 1) //add if r is negative
 122             r = left + right;
 123         else    //subtract if r is positive
 124             r = left - right;
 125         q = {q[14:0],!r[17]};
 126     end
 127     sqrt = q;   //final assignment of output.
 128 end
 129 endfunction //end of Function
 130
 131
 132 c version (from paper linked from URL)
 133
 134 unsigned squart(D, r) /*Non-Restoring sqrt*/
 135     unsigned D; /*D:32-bit unsigned integer to be square rooted */
 136     int *r;
 137 {
 138     unsigned Q = 0; /*Q:16-bit unsigned integer (root)*/
 139     int R = 0; /*R:17-bit integer (remainder)*/
 140     int i;
 141     for (i = 15;i>=0;i--) /*for each root bit*/
 142     {
 143         if (R>=0)
 144         { /*new remainder:*/
 145             R = R<<2)|((D>>(i+i))&3);
 146             R = R-((Q<<2)|1); /*-Q01*/
 147         }
 148         else
 149         { /*new remainder:*/
 150             R = R<<2)|((D>>(i+i))&3);
 151             R = R+((Q<<2)|3); /*+Q11*/
 152         }
 153         if (R>=0) Q = Q<<1)|1; /*new Q:*/
 154         else Q = Q<<1)|0; /*new Q:*/
 155     }
 156
 157     /*remainder adjusting*/
 158     if (R<0) R = R+((Q<<1)|1);
 159     *r = R; /*return remainder*/
 160     return(Q); /*return root*/
 161 }
 162
 163 From wikipedia page:
 164
 165 short isqrt(short num) {
 166     short res = 0;
 167     short bit = 1 << 14; // The second-to-top bit is set: 1 << 30 for 32 bits
 168
 169     // "bit" starts at the highest power of four <= the argument.
 170     while (bit > num)
 171         bit >>= 2;
 172
 173     while (bit != 0) {
 174         if (num >= res + bit) {
 175             num -= res + bit;
 176             res = (res >> 1) + bit;
 177         }
 178         else
 179             res >>= 1;
 180         bit >>= 2;
 181     }
 182     return res;
 183 }
 184
 185 """