[ET Trac] [Einstein Toolkit] #2015: thorn Vectors does not provide a sum() reduction

[Einstein Toolkit]

#2015: thorn Vectors does not provide a sum() reduction
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  Reporter:  rhaas        |       Owner:                     
      Type:  enhancement  |      Status:  new                
  Priority:  minor        |   Milestone:                     
 Component:  Cactus       |     Version:  development version
Resolution:               |    Keywords:  Vectors            
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Comment (by eschnett):

 I would implement {{{sum}}} via a sequence of shuffle and vector-add
 instructions, where the last add can be a scalar add:
 {{{
 // assuming vector size is 4, input is s4
 t4 = __builtin_shuffle(s4, {1,0,3,2});
 s2 = s4 + t4;
 t2 = __builtin_shuffle(s4, {2,3,0,1});
 s1 = s2 + t2;
 }}}

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Ticket URL: <https://trac.einsteintoolkit.org/ticket/2015#comment:3>
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