How can I optimize vector normalization in a Molecular Modeling program?

Semler semler at removethis.ioi.dk
Tue Nov 9 12:19:49 EST 1999

```The MS Visual C++ version of sqrt is quite slow. Converting you routine to
assembly would speed this up.

about 20 clocks to complete while
fmul takes 1 clock.

>Hi, I've been working on a molecular modeling program and have been
>trying to improve its performance recently.  I did some profiling and
>found that the most time by far (41.4%) was spent in a function which
>normalizes a 3-dimensional vector (profiling statistics are given at
>the bottom).
>
>I am wondering if anyone has suggestions for optimizing that operation.
>Thanks,
>William Knight
>willkn at montana.com
>
>The definition of the function is given below:
>
>typedef double VTYPE;
>typedef VTYPE Vector[3];
>
>
>////////////////////////////////////////////////////////////////////////
>////////
>// MakeUnitVector
>//
>// Reduces a normal vector specified as a set of three coordinates,
>// to a unit normal vector of length one.
>//
>bool MakeUnitVector(Vector v)
> {
> VTYPE length;
>
> // Calculate the length of the vector
> length = (VTYPE)sqrt((v[0]*v[0]) + (v[1]*v[1]) + (v[2]*v[2]));
>
> // if length is zero, bail
> if(length == 0)
> return false;
>
> // Divide each element by the length to get a unit vector.
> v[0] /= length;
> v[1] /= length;
> v[2] /= length;
>
> return true;
> }// MakeUnitVector
>
>//***************** Profiling Details ************//
>
>        Func          Func+Child           Hit
>        Time   %         Time      %      Count  Function
>---------------------------------------------------------
>   15493.876  41.4    15493.876  41.4  9971880 MakeUnitVector(double *
>const) (vector.obj)
>    5951.749  15.9     6789.747  18.1   627030
>CForceField::CalcVanderwaalsInteraction(void) (cforcefield.obj)
>    2185.047   5.8    18425.737  49.2    84010
>CForceField::CalcPotentialsAndForces(class CFFPairList *,class
>CEEPairList *,class CEOPairList *) (cforcefield.obj)
>    1976.562   5.3    13039.435  34.8  3752280
>CForceField::CalcEEInteraction(class CElectron *,class CElectron *)
>(cforcefield.obj)
>    1778.265   4.7     1778.265   4.7  4656515 VectorMagnitude(double *
>const) (vector.obj)
>    1668.910   4.5     1668.910   4.5  8884682 MultiplyVector(double *
>const,double) (vector.obj)
>    1270.428   3.4     1270.428   3.4 13438760 SubtractVector(double *
>const,double * const) (vector.obj)
>    1195.278   3.2     1195.278   3.2 21288242 AddVector(double *
>const,double * const) (vector.obj)
>    1145.663   3.1     1238.959   3.3       64 CStatus::Print(char *)
>(cstatus.obj)
>
>
>
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