similar to Fletch's version:

#                      1         2         3         4         5      
+   6
#            012345678901234567890123456789012345678901234567890123456
+7890123456789
my @result = @arr[grep{defined}map{$i++;$_?$i-1:undef}split"",sprintf(
+"%08b",0x2b)];
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