Changeset 7034

Timestamp:

May 14, 2009, 1:44:08 PM (14 years ago)

Author:

ole

Message:

Comments on the fast sqrt approximations. They don't give speedup on AMD 64, so have been left alone until further notice.
Timings included in the code.

File:

• anuga_core/source/anuga/shallow_water/shallow_water_ext.c (modified) (2 diffs)

anuga_core/source/anuga/shallow_water/shallow_water_ext.c

@@ -223 +223 @@
 
 
-// Optimised squareroot computation (double version, slower)
+// Optimised squareroot computation (double version)
 double Xfast_squareroot_approximation(double number) {
   double x;
@@ -323 +323 @@
   
   // Code to use fast square root optimisation if desired.
+  // Timings on AMD 64 for the Okushiri profile gave the following timings
+  //
+  // SQRT           Total    Flux
+  //=============================
+  //
+  // Ref            405s     152s
+  // Fast (dbl)     453s     173s
+  // Fast (sng)     437s     171s
+  //
+  // Consequently, there is currently (14/5/2009) no reason to use this 
+  // approximation.
+  
   //soundspeed_left  = fast_squareroot_approximation(g*h_left);
   //soundspeed_right = fast_squareroot_approximation(g*h_right);