Path: utzoo!attcan!uunet!dino!hascall
From: hascall@cs.iastate.edu (John Hascall)
Newsgroups: comp.graphics
Subject: Re: Mandelbrot algorithm summary
Keywords: mandelbrot algorithm
Message-ID: <536@dino.cs.iastate.edu>
Date: 7 Feb 90 15:42:35 GMT
References: <5480@vax1.tcd.ie>
Sender: usenet@dino.cs.iastate.edu
Organization: Iowa State Univ. Computation Center
Lines: 19

In article <5480@vax1.tcd.ie> cbuckley@vax1.tcd.ie (Colm Buckley) writes:
      
    [using 32bit fixed point for mandelbrot computations]

}The numbers are stored multiplied by 2**28, ...
 
    [addition and subtraction work ok, but muliply...]

}poses a problem. When two numbers stored in this fashion are multiplied
}together, the result will be 2**28 times too big ( (x * 2**28) * (y * 2**28) =
}(x * y * 2**56), not (x * y * 2**28). Therefore, when multiplication is
}necessary, the multiplicand and multiplier must both be divided by (2**14).
}This is easily and quickly accomplished by right-shifting x and y by 14 bits
}(x >> 14 = x / (2**14) ).
      
     Umm, when you right shift aren't you losing a great deal of
     your precision?  Or am I missing something here?

John Hascall