Sorting & Searching: x⍳x Index   <<   >>

 
   x←(2*¯24)ׯ1e9+?1e6⍴2e9
   y←(⍴x)⍴x

   cmpx 'x⍳x' 'x⍳y'
  x⍳x → 3.91E¯1 |   0% ⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕
  x⍳y → 6.57E¯1 | +68% ⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕

Self-classification or self-identification.
Currently x⍳x is optimized only for 64-bit floats.