From Manta

Hints for writting SIMD code in Manta

SSE or more generically SIMD code segments in Manta are placed in #ifdef blocks. These blocks are used if the cmake variable MANTA_REAL is set to float and the cmake variable MANTA_SSE is enabled.

Generic SIMD Code Template

Most SIMD code in manta performs operations on ray packet elements. This code usually follows the form:

 #ifdef MANTA_SSE
 
 int b = (rays.rayBegin + 3) & (~3);
 int e = rays.rayEnd & (~3);
 
 // Check to see if there are less than 4 elements.
 if (b == e) {
 
   // Iterate over all of the rays.
   for(int i=rays.rayBegin;i<rays.rayEnd;i++) {
     // NON-SIMD CODE.
   }
 
 } else {
   int i = rays.rayBegin;
 
   // Do the non aligned in front
   for(;i<b;++i) {
     // NON-SIMD CODE
   }
     
   // Do the aligned in the middle
   for(;i<e;i+=4) {
     // SIMD CODE
   }
     
   // Do the non aligned in end
   for(;i<rayEnd;++i) {
     // NON-SIMD CODE
   }
 
 }
 
 #else
   
 // NON-SIMD CODE
 
 #endif