Math::sqrt() not cutting it

Math::sqrt() not cutting it

• Marko B. Simic

  You might be able to roll your own by wrapping sqrtl();

  Which uses a long double

  Dan

  
  

• Jim Perry

  Sorry, I opened my big newbie mouth, it seems sqrtl() still returns an 8 byte value which is the same precision you get with a double

  Dan

  
  

• tweetys

  The problem is double is the largest floating point type available. If you want to have higher precision then you have to use a different method for storing the values.

  What are you trying to calculate the square root of which makes you need such high precision, and why do you need it with that kind of precision.

  
  
  

• kjak

  Why not roll your own that returns a decimal type
  
  Here's some pseudocode that uses the Newton Rhapson method. There's an optimal seed for this, but I don't remember off the top of my head:
  
  decimal sqrt_decimal(decimal inbound, double dNumDecimalsPrecision)
  {
  // Probably want to check for a negative number, or do you want imaginary results too
  double dActualPrecision = 0;
  decimal dCurrentEstimate = 2.; // Seed this with something good.
  decimal dPreviousEstimate = -1;
  decimal dCheckValue = 10 ^ (-dNumDecimalsPrecision);
  bool bFound = false;
  while (!bFound)
  {
  // Depending on how fast you want this to go, you may want to throw in a counter and break out if it takes too long.
  dPreviousEstimate = dCurrentEstimate;
  dCurrentEstimate = dCurrentEstimate - ((dCurrentEstimate ^ 2 - inbound ^ 2)/(2 * dCurrentEstimate));
  if (dCheckValue > Abs(dCurrentEstimate - dPreviousEstimate))
  {
  bFound = true;
  }
  }
  return dCurrentEstimate
  }
  
  

• Jon Watte

  Sounds good, how could I go about doing that What is the sqrt algorithim

  
  

• wEmmay

  Hello

  Re: Math::sqrt() not cutting it

  Please do not post the same question in multiple forums (http://forums.microsoft.com/MSDN/ShowPost.aspx PostID=1063426&SiteID=1)

  This question is outside the scope of this forum - for the scope of the VC General forum please look at: http://forums.microsoft.com/MSDN/ShowPost.aspx PostID=19445&SiteID=1

  The other forum is a better match for your question.

  OTP

  Thanks

  Damien

  
  
  
• Math::sqrt() not cutting it