c++ - Most efficient way of accessing coordinates -


given following definition

union {   double coords[3];   struct {     double x,y,z;   }; } p;

it possible access coordinates of 3d point both index , name (both ways have advantages). equivalent? more precisely: following expressions

... p.coords[0] ... p.x ... ... p.coords[1] ... p.y ... ... p.coords[2] ... p.z ...

(pairwise, each line) generate same (assembly) code? there difference in efficiency between 2 ways of accessing coordinate?

p.x,... might faster, there's not difference 1 notice. when use array, there time spent on multiplication size of each double in given index desired memory address; in other method (p.x,...) compiler knows address accessing calculation not required. however, if compiler smart enough figure out constant numbers, there no difference.


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