removed exponential table lookup by default. Has been replaced by a s…

…imple call to exp.

CHANGES.txt

@@ -17,6 +17,10 @@ NEW IN VERSION 2
   particular system. This option is altered using the "-p" command line option
   on the CUDA version (defaults to 100).
 
+- Exponential Table lookup has been disabled by default. It was found that
+  on most architectures, it's actually faster to just do the EXP call than
+  it is to have to read from memory.
+
 ===============================================================================
 NEW IN VERSION 1
 ===============================================================================

src/cpu/kernel.c

@@ -214,7 +214,10 @@ void attenuate_segment( Input * restrict I, Source * restrict S,
 	#pragma vector_level(10)
 	#endif
 	for( int g = 0; g < egroups; g++)
-		expVal[g] = interpolateTable( table, tau[g] );  
+	{
+		//expVal[g] = interpolateTable( table, tau[g] );  
+		expVal[g] = 1.f - exp( -tau[g] ); // exp is faster on many architectures
+	}
 
 	// Flux Integral
 

src/cuda/kernel.cu

@@ -155,7 +155,8 @@ __global__ void run_kernel( Input I, Source *  S,
 		tau = sigT * ds;
 		sigT2 = sigT * sigT;
 
-		interpolateTable( table, tau, &expVal );  
+		//interpolateTable( table, tau, &expVal );  
+		expVal = 1.f - exp( -tau); // EXP function is fater than table lookup
 
 		// Flux Integral