Path: chuka.playstation.co.uk!news
From: "Jon Prestidge  (Jon@surfed.to)" <jon@surfed.to>
Newsgroups: scee.yaroze.freetalk.english
Subject: Re: Maths Functions?
Date: Mon, 27 Aug 2001 16:53:40 +0100
Organization: PlayStation Net Yaroze (SCEE)
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Here's a square root I did a long time ago -- it's probably too slow for
'in-game' calculations allthough fine for using in initialization phases.
It first approximates to a straight line and then tests the values until it
finds the right on.


int integer_square_root( int n )
   {
   // V1.0  Jon Prestidge 1997

   register int i;
   register int square;
   register int previous_square;

   if ( n < 0 )
      {
      #if DIAGNOSTICS_REQUIRED
         err_dis( 129 );
      #endif
      return 0;
      }
   if ( !n ) return 0;  // square root of zero is zero,

   i = 0;
   if ( n > 99 && n < 300 ) i = 10;
   if ( n > 299 && n < 400 ) i = 17;
   if ( n > 399 && n < 1970 ) i = ( n / 64 ) + 13;
   if ( n > 1969 && n < 9450 ) i = ( n / 128 ) + 23;
   if ( n > 9449 && n < 27000 ) i = ( n / 256 ) + 58;
   if ( n > 26999 ) i = ( n / 512 ) + 112;
   if ( n > 120000 )
      {
      #if DIAGNOSTICS_REQUIRED
         err_dis( 130 );
      #endif
      return i;
      }
   if ( i > 0 ) i--;
   square = i * i;
   while ( n > square )
      {
      previous_square = square;
      i++;
      square = i * i;
      }

   if ( n - previous_square < square - n ) i = i - 1;
   // printf( "square-root of %d is %d\n", n, i );
   return i;

   }